A thread-pool class for managing tasks in multi-threaded programs. More...

#include <c++-gtk-utils/task_manager.h>

Classes
class	IncHandle
	A scoped handle for exception safe incrementing of the maximum number of threads that a TaskManager object will run. More...

Public Types
enum	StopMode { wait_for_running, wait_for_all }

Public Member Functions
	TaskManager (const TaskManager &)=delete

TaskManager &	operator= (const TaskManager &)=delete

unsigned int	get_max_threads () const

unsigned int	get_min_threads () const

unsigned int	get_used_threads () const

void	set_max_threads (unsigned int max)

void	change_max_threads (int delta)

unsigned int	get_tasks () const

unsigned int	get_idle_time () const

void	set_idle_time (unsigned int idle)

bool	get_blocking () const

void	set_blocking (bool blocking)

StopMode	get_stop_mode () const

void	set_stop_mode (StopMode mode)

void	stop_all ()

void	add_task (const Callback::Callback *task)

void	add_task (std::unique_ptr< const Callback::Callback > task, std::unique_ptr< const Callback::Callback > fail)

bool	is_error () const

template<class Ret , class... Params, class... Args, class T >
Cgu::SharedLockPtr< Cgu::AsyncResult< Ret > >	make_task_result (T &t, Ret(T::*func)(Params...), Args &&... args)

template<class Ret , class... Params, class... Args, class T >
void	make_task_when_full (std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> when, Cgu::Releaser when_releaser, std::unique_ptr< const Cgu::Callback::Callback > fail, Cgu::Releaser fail_releaser, gint priority, GMainContext context, T &t, Ret(T::func)(Params...), Args &&... args)

template<class Ret , class... Params, class... Args, class T >
void	make_task_when (std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> when, GMainContext context, T &t, Ret(T::func)(Params...), Args &&... args)

template<class Ret , class... Params, class... Args, class T >
Cgu::SharedLockPtr< Cgu::AsyncResult< Ret > >	make_task_result (const T &t, Ret(T::*func)(Params...) const, Args &&... args)

template<class Ret , class... Params, class... Args, class T >
void	make_task_when_full (std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> when, Cgu::Releaser when_releaser, std::unique_ptr< const Cgu::Callback::Callback > fail, Cgu::Releaser fail_releaser, gint priority, GMainContext context, const T &t, Ret(T::func)(Params...) const, Args &&... args)

template<class Ret , class... Params, class... Args, class T >
void	make_task_when (std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> when, GMainContext context, const T &t, Ret(T::func)(Params...) const, Args &&... args)

template<class Ret , class... Params, class... Args>
Cgu::SharedLockPtr< Cgu::AsyncResult< Ret > >	make_task_result (Ret(*func)(Params...), Args &&... args)

template<class Ret , class... Params, class... Args>
void	make_task_when_full (std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> when, Cgu::Releaser when_releaser, std::unique_ptr< const Cgu::Callback::Callback > fail, Cgu::Releaser fail_releaser, gint priority, GMainContext context, Ret(func)(Params...), Args &&... args)

template<class Ret , class... Params, class... Args>
void	make_task_when (std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> when, GMainContext context, Ret(func)(Params...), Args &&... args)

template<class Ret , class Func >
Cgu::SharedLockPtr< Cgu::AsyncResult< Ret > >	make_task_result (Func &&f)

template<class Ret , class Func >
void	make_task_when_full (std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> when, Cgu::Releaser when_releaser, std::unique_ptr< const Cgu::Callback::Callback > fail, Cgu::Releaser fail_releaser, gint priority, GMainContext *context, Func &&func)

template<class Ret , class Func >
void	make_task_when (std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> when, GMainContext *context, Func &&f)

template<class Ret , class Func >
void	make_task_compose (Func &&f, GMainContext *context, std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >> when)

	TaskManager (unsigned int max=8, unsigned int min=0, unsigned int idle=10000, bool blocking=true, StopMode mode=TaskManager::wait_for_all)

	~TaskManager ()

Static Public Member Functions
static unsigned int	get_max_tasks ()

Detailed Description

A thread-pool class for managing tasks in multi-threaded programs.

See also: Cgu::Thread::Future Cgu::AsyncResult Cgu::AsyncQueueDispatch Cgu::AsyncChannel Cgu::Callback::post() Cgu::Thread::TaskManager::IncHandle Cgu::Thread::parallel_for_each() Cgu::Thread::parallel_for_each_partial() Cgu::Thread::parallel_transform() Cgu::Thread::parallel_transform_partial()

Cgu::Thread::Future operates on the principle of there being one worker thread per task. In some cases however, it may be better to have a limited pool of worker threads executing a larger number of tasks. This class implements this approach via a thread pool.

One common approach for thread pools of this kind is to set the maximum number of threads to the number of cores, or some number less than the number of cores, available on the local machine. How that can be determined is system specific (on linux it can be obtained by, for example, counting the 'processor' fields in /proc/cpuinfo or by using sysconf with the glibc extension for _SC_NPROCESSORS_ONLN). From version 2.36, glib has a g_get_num_processors() function. From gcc-4.7, C++11's std::thread::hardware_concurrency() static member function is also available.

The most general way of creating a new task is to call TaskManager::add_task() with a Callback::Callback object (say, as constructed by Callback::lambda() from a callable object such as a lambda expression or the return value of std::bind). Where the task needs to provide a result, two approaches can be adopted. First, the task callback can have a Cgu::AsyncResult object held by Cgu::SharedLockPtr (or by std::shared_ptr having a thread safe reference count) bound to it. Alternatively, a task can provide a result asynchronously to a glib main loop by calling Cgu::Callback::post() when it is ready to do so. From version 2.0.13, the TaskManager::make_task_result(), TaskManager::make_task_when(), TaskManager::make_task_when_full() and TaskManager::make_task_compose() convenience wrapper methods are provided which will set this up for you (including constructing appropriate task callbacks). This would normally be done by passing one of those functions a callable object which returns a value, such as a lambda expression or the return value of std::bind. Tasks can add other tasks, enabling the composition of an arbitrary number of tasks to obtain a final result.

With version 2.0.13 of the library, if a callable object which was not a std::function object was passed, the return value had to be explicitly stated in the call to make_task_*(). So, if a lambda expression returning an int was to be executed as a task, TaskManager::make_task_result<int>(), TaskManager::make_task_when_full<int>(), TaskManager::make_task_when<int>() or TaskManager::make_task_compose<int>() had to be called. This is no longer necessary with version 2.0.14: the return value will be deduced automatically if it is not stated.

Overloads of TaskManager::make_task_result(), TaskManager::make_task_when() and TaskManager::make_task_when_full() (but not TaskManager::make_task_compose()) also exist which take a function pointer (or an object reference and member function pointer) to a function which returns a value, with bound arguments, but these offer little advantage over using std::bind, so generally it is easier to pass a callable object. These overloads can take up to three bound arguments in the case of a non-static member function, and four bound arguments in the case of any other function. In the case of a non-static member function, the referenced object whose member function is to be called must remain in existence until the task has completed. The target function passed by pointer (or member function pointer) can take a reference to const argument, as a copy of the object to be passed to the argument is taken to avoid dangling references, but it cannot take a reference to non-const argument.

Copying of the return value of the target function or callable object represented by the task may take place when using TaskManager::make_task_result(), TaskManager::make_task_when(), TaskManager::make_task_when_full() and TaskManager::make_task_compose(). When a task completes, the return value will be stored, either in a Cgu::AsyncResult object (if TaskManager::make_task_result() is called) or for the purposes of executing the 'when' callback in a glib main loop (if TaskManager::make_task_when(), TaskManager::make_task_when_full() or TaskManager::make_task_compose() are called). This storage will therefore cause the return value type's assignment operator or copy constructor to be called once unless that type has a move assignment operator or move constructor, in which case a move operation will be made where possible. Note that a 'when' callback takes the stored return value by reference to const and so without any additional copying upon the 'when' callback being executed in the main loop.

TaskManager objects do not provide thread cancellation. Thread cancellation is incompatible with the task-centred thread pool model. If task cancellation is wanted, use a Cgu::Thread::Future (or Cgu::Thread::Thread or Cgu::Thread::JoinableHandle) object instead, and have a dedicated thread for the cancelable task.

If glib < 2.32 is installed, g_thread_init() must be called before any TaskManager objects are constructed, which in turn means that with glib < 2.32 TaskManager objects may not be constructed as static objects in global namespace (that is, before g_thread_init() has been called in the program).

Any exceptions which propagate from a task will be consumed to protect the TaskManager object, and to detect whether this has happened there is a version of the TaskManager::add_task() method which takes a second argument comprising a 'fail' callback. If an exception propagates from the 'fail' callback that is also consumed and a g_critical() message issued. TaskManager::make_task_when_full() also provides for a 'fail' callback.

Tasks can be aborted by throwing Cgu::Thread::Exit (as well as any other exception). Where a task is managed by a TaskManager object, throwing Cgu::Thread::Exit will only terminate the task and not the thread on which it is running (and will cause the 'fail' callback to be executed, if there is one).

Any 'fail' callback passed to TaskManager::add_task() or TaskManager::make_task_when_full() must be fully bound. Whilst a task can pass error status to the 'fail' callback via shared data bound to both the task and the 'fail' callback (held by, say, a SharedLockPtr object), or a global error stack, 'fail' callbacks are generally best reserved for use with entirely unexpected exceptions, where the most reasonable course is to perform some orderly logging and shutdown. For handlable exceptions, in an asynchronous environment the best course is often to catch them and deal with them in the task itself and (where TaskManager::make_task_when_full(), TaskManager::make_task_when() or TaskManager::make_task_compose() is employed) return a value of the task function's return type indicating no result.

TaskManager objects have no copy constructor or copy assignment operator, as copying them would have no obvious semantic meaning. Whilst swapping or moving TaskManager objects would be meaningful, this is not implemented either because it would require an additional internal lock to be thread safe, and the circumstances in which moving or swapping would be useful are limited. Where a move option is wanted, a TaskManager object can be constructed on free store and held by std::unique_ptr.

Here is a compilable example of the calculator class referred to in the documentation on the AsyncResult but which uses a TaskManager object so that the calculator class can run more than one thread to service its calculations, using TaskManager::make_task_result():

#include <vector>
#include <numeric>
#include <ostream>
#include <iostream>
 
#include <glib.h>
 
#include <c++-gtk-utils/task_manager.h>
#include <c++-gtk-utils/async_result.h>
#include <c++-gtk-utils/shared_ptr.h>
#include <c++-gtk-utils/callback.h>
 
using namespace Cgu;
 
class Calcs {
  Thread::TaskManager tm;
public:
  SharedLockPtr<AsyncResult<double>> mean(const std::vector<double>& nums) {
    return tm.make_task_result([=]() -> double {
        if (nums.empty()) return 0.0;
    return std::accumulate(nums.begin(), nums.end(), 0.0)/nums.size();
      });
  }
 
  // ... other calculation methods here
};
 
int main () {
 
  g_thread_init(0);
  Calcs calcs;
  auto res1 = calcs.mean({1, 2, 8, 0});
  auto res2 = calcs.mean({101, 53.7, 87, 1.2});
 
  // ... do something else
  std::cout << res1->get() << std::endl;
  std::cout << res2->get() << std::endl;
 
}

Here is a reimplementation, using TaskManager::make_task_when(), of the Number class example with get_primes() method given in the documentation for Cgu::Thread::Future:

std::vector<long> get_primes(int n); // calculates the first n primes
 
// get the first 1,000 primes
using namespace Cgu;
 
Thread::TaskManager tm;
auto when = Callback::to_unique(
  Callback::lambda<const std::vector<long>&>([] (const std::vector<long>& result) {
    for (const auto& elt: result) {std::cout << elt << std::endl;}
  })
);
tm.make_task_when(std::move(when),
                  0,                    // default main loop context
                  [] () {return get_primes(1000);});

Where a task running on a TaskManager object is to block, the TaskManager::IncHandle scoped handle class can be used to increment the maximum number of threads running on the object's thread pool temporarily while blocking takes place, so as to enable another thread to keep a core active. This can be useful where a task is to 'join' on another task when composing tasks: and it is usually essential to increment the maximum thread count temporarily where a task is to block on one of its sub-tasks, to avoid any possibility of deadlock through thread starvation (thread starvation occurs where all threads on a thread pool are occupied by tasks blocking on sub-tasks which have still to run on the thread pool, and which cannot run because the maximum thread count has been reached). Here is a compilable example:

#include <iostream>
#include <ostream>
#include <utility>
#include <memory>
 
#include <glib.h>
 
#include <c++-gtk-utils/task_manager.h>
#include <c++-gtk-utils/callback.h>
 
using namespace Cgu;
 
// simulate a blocking operation, say from a server, with g_usleep()
int mult(int x, int y) {
  g_usleep(100000);
  return x * y;
}
 
int main(int argc, char* argv[]) {
 
  g_thread_init(0);
  Thread::TaskManager tm{1}; // only one thread available unless blocking!
  GMainLoop* loop = g_main_loop_new(0, true);
 
  auto when = Callback::to_unique(
    Callback::lambda<const int&>([loop] (const int& res) {
      std::cout << res << std::endl;
      g_main_loop_quit(loop);
    })
  );
 
  tm.make_task_when(
    std::move(when),
    0, // default main loop
    [&tm] () -> int {
      // this task multiplies 'a' by 2 and 'b' by 3, and adds the products 
      int a = 10;
      int b = 12;
 
      // increment maximum thread count before launching sub-task and
      // then blocking
      Thread::TaskManager::IncHandle h{tm};
      // start a sub-task
      auto sub = tm.make_task_result([a, &tm] () -> int {
        // increment maximum thread count again before blocking in
        // this task (pretend that some other task in the program
        // may also want to run while both the parent task and this
        // task block on mult())
        Thread::TaskManager::IncHandle h{tm};
        return mult(a, 2);
      });
 
      int res = mult(b, 3)
      return sub->get() + res;
    }
  );
 
  g_main_loop_run(loop);
}

An alternative to using TaskManager::IncHandle for sub-tasks is to run the sub-tasks on their own threads via Thread::Future or std::async().

Rate limiting

Resources are not infinite and there is a hard limit to the number of tasks that a TaskManager object may have queued for execution at any one time. From version 2.0.31 the limit to the number of running and queued tasks may be obtained by calling the TaskManager::get_max_tasks() method (note that particularly on 32-bit systems it will in practice be impossible to reach this limit because of memory exhaustion: the value returned by that method represents the limit enforced by TaskManager irrespective of the actual available memory at the system or process level and any intervention of std::bad_alloc exceptions). If that limit is exceeded, the TaskManager::add_task() and TaskManager::make_task_* methods will throw std::length_error.

In practice however, on most systems such a large number of queued tasks (normally around 4,294,967,295 for 64-bit systems) is likely to be unfeasible and program logic constraints will be exceeded long before the limit is reached, even if available memory is not. In some usages therefore, some form of rate limiting may be needed to prevent a work-producing thread overwhelming a TaskManager object by continuously adding more tasks for execution than the object's throughput capacity is capable of dealing with, so pushing the number of unexecuted tasks to an excessive level.

TaskManager objects provide no built-in rate limiting (other than throwing the std::length_error exception referred to above). This is because there is no one-size-fits-all way of doing so. One common approach is to apply throttling to threads which add tasks by enforcing a wait in their thread of execution when the level of queued tasks reaches too high a level, so hindering their ability to add new ones. However this is counter productive where it is a task running on the TaskManager object which is adding the new tasks, particularly with a TaskManager object having only a few threads running in its pool. Another approach is to throw an exception when adding tasks which exceed a user-selectable level which is much lower than the value returned by TaskManager::get_max_tasks(), but this would make it more difficult to use the Cgu::Thread::parallel_for_each() and Cgu::Thread::parallel_transform() functions provided by this library.

The best approach is for user code to provide its own rate limiting in cases where the way that that code is organised means that it could produce an excessive number of accumulating unexecuted tasks, possibly by applying delays when unexecuted tasks rise in number excessively, using timeouts with a glib main loop. This may be checked for by having code call the TaskManager::get_tasks() method before adding a significant batch of new tasks in order to test queue size, and if necessary postpone adding the new tasks until the size of the already accumulated tasks has reduced.

The Cgu::AsyncChannel class has emplace() and push() methods which will block when a channel is full. That class can therefore be used for rate limiting function objects pushed onto the channel in cases where that is an appropriate alternative solution to TaskManager.

Member Enumeration Documentation

◆ StopMode

enum Cgu::Thread::TaskManager::StopMode

Enumerator
wait_for_running
wait_for_all

Constructor & Destructor Documentation

◆ TaskManager() [1/2]

Cgu::Thread::TaskManager::TaskManager ( const TaskManager & )

delete

This class cannot be copied. The copy constructor is deleted.

◆ TaskManager() [2/2]

Cgu::Thread::TaskManager::TaskManager	(	unsigned int	max = `8`,
		unsigned int	min = `0`,
		unsigned int	idle = `10000`,
		bool	blocking = `true`,
		StopMode	mode = `TaskManager::wait_for_all`
	)

If the specified minimum number of threads is greater than 0, this constructor will start the required minimum number of threads. If glib < 2.32 is installed, g_thread_init() must be called before any TaskManager objects are constructed

Parameters

max	The maximum number of threads which the TaskManager object will run in the thread pool. If the value passed as this argument is less than the value passed as 'min', the maximum number of threads will be set to 'min'. A value of 0 is not valid, and if this is passed the number will be set to the greater of 1 and 'min'.
min	The minimum number of threads which the TaskManager object will run in the thread pool. In cases where it is important that, if starting a new thread in the pool were to fail, any tasks which were queued for execution before the failure occurred will still run to completion (say, because the failure exception is to be caught and 'blocking' is true), a 'min' value of at least 1 will ensure that a thread remains available in the pool for that purpose. (See the Note below for more about this.)
idle	The length of time in milliseconds that threads greater in number than 'min' and not executing any tasks will remain in existence. The default is 10000 (10 seconds).
blocking	If true, calls to stop_all() and the destructor will not return until the tasks remaining to be executed have finished (what is meant by "the tasks remaining to be executed" depends on the StopMode setting, for which see the documentation on the stop_all() method). If false, stop_all() and the destructor will return straight away (which in terms of the TaskManager class implementation is safe for the reasons explained in the documentation on the destructor).
mode	The StopMode setting (either Cgu::Thread::TaskManager::wait_for_running or Cgu::Thread::TaskManager::wait_for_all) executed when running stop_all() or when the destructor is called. See the documentation on stop_all() for an explanation of the setting.

Exceptions

std::bad_alloc	This exception might be thrown if memory is exhausted and the system throws in that case.
Cgu::Thread::TaskError	This exception will be thrown if starting the specified minimum number of threads fails.
Cgu::Thread::MutexError	This exception might be thrown if initialisation of the contained mutex fails. (It is often not worth checking for this, as it means either memory is exhausted or pthread has run out of other resources to create new mutexes.)
Cgu::Thread::CondError	This exception might be thrown if initialisation of the contained condition variable fails. (It is often not worth checking for this, as it means either memory is exhausted or pthread has run out of other resources to create new condition variables.)

Note: If 'min' is 0, even though tasks are outstanding in the pool there could be 0 threads left running in the pool to complete them if all of the following improbable events occur together: (i) a thread has increased the maximum number of threads set for the pool via change_max_threads() or set_max_threads() at a time when tasks are queued for execution, so that an attempt is made to start new threads, (ii) a different thread has concurrently attempted, using one of those methods, to reduce the maximum number of threads set for the pool by an amount equal to or greater than the original maximum thread number prevailing before these two concurrent operations, (iii) concurrently with those two events a number of tasks equal to the original maximum thread number referred to in ii above happen to have finished, and (iv) the call to change_max_threads() or set_max_threads() referred to at i above throws an exception and all of the threads attempted to be started there fail to start. If usage of a TaskManager object could result in all these things occurring, setting its 'min' value to 1 will ensure that there is always at least one thread available in the pool which can complete any outstanding tasks which had been added to the object before the exception was thrown.

Since 2.0.12

◆ ~TaskManager()

Cgu::Thread::TaskManager::~TaskManager ( )

The destructor will call stop_all(), unless that method has previously been called explicitly without throwing std::bad_alloc. If the blocking setting is true, the destructor will not return until the tasks remaining to be executed have finished (what is meant by "the tasks remaining to be executed" depends on the StopMode setting, for which see the documentation on the stop_all() method.) If the blocking setting is false, the destructor will return straight away: this is safe, because TaskManager's internals for running tasks have been implemented using reference counting and will not be deleted until all threads running on the TaskManager object have finished, although the remaining tasks should not attempt to call any of TaskManager's methods once the TaskManager object itself has been destroyed.

The destructor is thread safe (any thread can destroy a TaskManager object) unless the blocking setting is true, in which case no task running on the TaskManager object may destroy the TaskManager object. Subject to that, it is not an error for a thread to destroy a TaskManager object and so invoke this destructor while another thread is already blocking in (if the blocking setting is true) or already out of (if the blocking setting is false) a call to stop_all() and remaining tasks are executing: if blocking, both calls (to stop_all() and to this destructor) would safely block together. Any given thread can similarly safely follow a non-blocking call to stop_all() by a non-blocking call to this destructor even though remaining tasks are executing. However, it is an error for a thread to call stop_all() after another thread has begun destruction of the TaskManager object (that is, after this destructor has been entered): there would then be an unresolvable race with the destructor.

The destructor will not throw.

If stop_all() has not previously been called explicitly and throws std::bad_alloc() when called in this destructor, the exception will be caught and consumed, but then the destructor will not block even if the blocking setting is true, and if the minimum number of threads is not 0 some threads might remain running during the entire program duration (albeit safely). Where the throwing of std::bad_alloc is a meaningful event (usually it isn't) and needs to be guarded against, call stop_all() explicitly before this destructor is entered, or use a minimum thread value of 0 and allow for the case of the destructor not blocking.

Since 2.0.12

Member Function Documentation

◆ add_task() [1/2]

void Cgu::Thread::TaskManager::add_task ( const Callback::Callback * task )

inline

This method adds a new task. If one or more threads in the pool are currently blocking and waiting for a task, then the task will begin executing immediately in one of the threads. If not, and the value returned by get_used_threads() is less than the value returned by get_max_threads(), a new thread will start and the task will execute immediately in the new thread. Otherwise, the task will be queued for execution as soon as a thread becomes available. Tasks will be executed in the order in which they are added to the ThreadManager object. This method is thread safe (any thread may call it, including any task running on the TaskManager object).

A task may terminate itself prematurely by throwing Cgu::Thread::Exit. In addition, the implementation of TaskManager will consume any other exception escaping from the task callback and safely terminate the task concerned in order to protect the integrity of the TaskManager object. Where detecting any of these outcomes is important (usually it won't be), the two argument version of this method is available so that a 'fail' callback can be executed in these circumstances.

Parameters

task A callback representing the new task, as constructed by the Callback::lambda(), Callback::make() or Callback::make_ref() factory functions. Ownership is taken of this callback, and it will be disposed of when it has been finished with. If an exception propagates from the task, the exception will be consumed and (if the thrown object's type is not Cgu::Thread::Exit) a g_critical() warning will be issued. The destructors of any bound arguments in the callback must not throw.

Exceptions

std::bad_alloc This exception will be thrown if memory is exhausted and the system throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). See also the documentation for the get_max_tasks() method about the possibility of std::length_error being thrown. If std::bad_alloc or std::length_error is thrown, the task will not start and the 'task' callback will be disposed of.

Cgu::Thread::TaskError This exception will be thrown if stop_all() has previously been called. It will also be thrown if this method tries but fails to start a new thread, or if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc or a thread has previously failed to start correctly. If this exception is thrown, the task will not start and the 'task' callback will be disposed of.

Since 2.0.12

◆ add_task() [2/2]

void Cgu::Thread::TaskManager::add_task	(	std::unique_ptr< const Callback::Callback >	task,
		std::unique_ptr< const Callback::Callback >	fail
	)

This method adds a new task. If one or more threads in the pool are currently blocking and waiting for a task, then the task will begin executing immediately in one of the threads. If not, and the value returned by get_used_threads() is less than the value returned by get_max_threads(), a new thread will start and the task will execute immediately in the new thread. Otherwise, the task will be queued for execution as soon as a thread becomes available. Tasks will be executed in the order in which they are added to the ThreadManager object. This method is thread safe (any thread may call it, including any task running on the TaskManager object).

A task may terminate itself prematurely by throwing Cgu::Thread::Exit. In addition, the implementation of TaskManager will consume any other exception escaping from the task callback and safely terminate the task concerned in order to protect the integrity of the TaskManager object. Where detecting any of these outcomes is important (usually it won't be), a callback can be passed to the 'fail' argument which will execute if, and only if, either Cgu::Thread::Exit is thrown or some other exception has propagated from the task. This 'fail' callback is different from the 'fail' callback of Cgu::Thread::Future objects (programming for many tasks to a lesser number of threads requires different approaches from programming for one thread per task), and it executes in the task thread rather than executing in a glib main loop (however, the 'fail' callback can of course call Cgu::Callback::post() to execute another callback in a main loop, if that is what is wanted).

Parameters

task A callback representing the new task, as constructed by the Callback::lambda(), Callback::make() or Callback::make_ref() factory functions. If an exception propagates from the task, the exception will be consumed and the 'fail' callback will execute.

fail A callback (as constructed by the Callback::lambda(), Callback::make() or Callback::make_ref() factory functions) which will be executed if the function or callable object executed by the 'task' callback exits by throwing Thread::Exit or some other exception. If an exception propagates from the 'fail' callback, this will be consumed to protect the TaskManager object, and a g_critical() warning will be issued.

Exceptions

std::bad_alloc This exception will be thrown if memory is exhausted and the system throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). See also the documentation for the get_max_tasks() method about the possibility of std::length_error being thrown. If std::bad_alloc or std::length_error is thrown, the task will not start (which also means that the 'fail' callback will not execute).

Cgu::Thread::TaskError This exception will be thrown if stop_all() has previously been called. It will also be thrown if this method tries but fails to start a new thread, or if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc or a thread has previously failed to start correctly. If this exception is thrown, the task will not start (which also means that the 'fail' callback will not execute).

Note: 1. Question: why does the single argument version of add_task() take a pointer, and this version take the callbacks by std::unique_ptr? Answer: The two argument version of add_task() takes its arguments by std::unique_ptr in order to be exception safe if the first callback to be constructed is constructed correctly but construction of the second callback object throws.; 2. If the library is compiled using the --with-auto-ptr configuration option, then this method's signature is add_task(std::auto_ptr<const Callback::Callback>, std::auto_ptr<const Callback::Callback>) in order to retain compatibility with the 1.2 series of the library.

Since 2.0.12

◆ change_max_threads()

void Cgu::Thread::TaskManager::change_max_threads ( int delta )

This will increase, or if 'delta' is negative reduce, the maximum number of threads which the TaskManager object will currently run in the thread pool by the value of 'delta'. The purpose of this is to enable a task to increment the maximum thread number where it is about to enter a call which may block for some time, with a view to decrementing it later when it has finished making blocking calls, so as to enable another thread to keep a core active. If 'delta' is negative and results in a max_threads value of less than the current number of running threads, the number of threads actually running will only be reduced as tasks complete, or as idle timeouts expire. This method does nothing if stop_all() has previously been called. This method is thread safe. Since version 2.0.18, the scoped handle class TaskManager::IncHandle is available which calls this method.

Parameters

delta The change (positive or negative) to the maximum number of threads which the TaskManager object will currently run in the thread pool. This method will not set the maximum value of threads to a value less than that returned by get_min_threads(), nor to a value less than 1.

Exceptions

std::bad_alloc	If this call is passed a positive value and tasks are currently queued for execution, a new thread or threads will be started for the queued tasks, so this exception may be thrown on starting a new thread if memory is exhausted and the system throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion).
Cgu::Thread::TaskError	If this call is passed a positive value and tasks are currently queued for execution, a new thread or threads will be started for the queued tasks, so this exception may be thrown on starting a new thread if it fails to start correctly (this would mean that memory is exhausted, the pthread thread limit has been reached or pthread has run out of other resources to start new threads).

Since 2.0.14

◆ get_blocking()

bool Cgu::Thread::TaskManager::get_blocking ( ) const

Gets the current blocking setting, which determines whether calls to stop_all() and the destructor will block waiting for all remaining tasks to complete. This value is established initially by the 'blocking' argument passed to the TaskManager constructor and can subequently be changed by calling set_blocking(). This method will not throw and is thread safe.

Returns: The current blocking setting.

Since 2.0.12

◆ get_idle_time()

unsigned int Cgu::Thread::TaskManager::get_idle_time ( ) const

Gets the length of time in milliseconds that threads greater in number than the minimum and not executing any tasks will remain in existence waiting for new tasks. This value is established initially by the 'idle' argument passed to the TaskManager constructor and can subequently be changed by calling set_idle_time(). The default value is 10000 (10 seconds). This method will not throw and is thread safe.

Returns: The idle time in milliseconds.

Since 2.0.12

◆ get_max_tasks()

static unsigned int Cgu::Thread::TaskManager::get_max_tasks ( )

inlinestatic

Gets the limit to the sum of the number of tasks which a TaskManager object may have running in the thread pool or queued for execution at any one time. On a 32-bit system, reaching this limit will normally cause the amount of memory which any process may allocate to be exceeded so the limit will in practice never be met (the add_task() or make_task_* methods will throw a std::bad_alloc exception before then). On a 64-bit system this limit will normally be the same as UINT_MAX (4,294,967,295 for a 32-bit unsigned int) which although likely to be unfeasibly large could in theory be reached with a system which can make around 70GB of memory available to the process for the TaskManager object. The add_task() and make_task_* methods will throw std::length_error if an attempt is made to exceed this limit and std::bad_alloc has not got there first.

This method is thread safe.

Returns: The maximum number of tasks which a TaskManager object may have either running or queued for execution at any one time.

Exceptions

std::bad_alloc This exception may be thrown the first time this method is called. Any subsequent calls will not throw if an earlier one did not (this method calculates the limit once only and then caches it using static local initialization).

Since 2.0.31

◆ get_max_threads()

unsigned int Cgu::Thread::TaskManager::get_max_threads ( ) const

Gets the maximum number of threads which the TaskManager object is currently set to run in the thread pool. This value is established initially by the 'max' argument passed to the TaskManager constructor and can subequently be changed by calling set_max_threads() or change_max_threads(). The default value is 8. This method will not throw and is thread safe. However, if a blocking task might use the TaskManager::IncHandle class (or increase and then decrease the number by hand by calling change_max_threads()), this method will not usually be useful.

Returns: The maximum number of threads.

Since 2.0.12

◆ get_min_threads()

unsigned int Cgu::Thread::TaskManager::get_min_threads ( ) const

Gets the minimum number of threads which the TaskManager object will run in the thread pool (these threads will last until stop_all() is called or the TaskManager object is destroyed). This value is established by the 'min' argument passed to the TaskManager constructor and cannot subequently be changed. The default is 0. This method will not throw and is thread safe.

Returns: The minimum number of threads.

Since 2.0.12

◆ get_stop_mode()

StopMode Cgu::Thread::TaskManager::get_stop_mode ( ) const

Gets the current StopMode setting (either Cgu::Thread::TaskManager::wait_for_running or Cgu::Thread::TaskManager::wait_for_all) executed when running stop_all() or when the destructor is called. See the documentation on stop_all() for an explanation of the setting. This value is established initially by the 'mode' argument passed to the TaskManager constructor and can subequently be changed by calling set_stop_mode(). This method will not throw and is thread safe.

Returns: The current StopMode setting.

Since 2.0.12

◆ get_tasks()

unsigned int Cgu::Thread::TaskManager::get_tasks ( ) const

Gets the number of tasks which the TaskManager object is at present either running in the thread pool or has queued for execution. This value will be less than the number returned by get_used_threads() if threads in the thread pool are currently waiting to receive tasks for execution. This method will not throw and is thread safe.

Returns: The number of tasks either running or queued for execution.

Since 2.0.12

◆ get_used_threads()

unsigned int Cgu::Thread::TaskManager::get_used_threads ( ) const

Gets the number of threads which the TaskManager object is currently running in the thread pool, including those blocking waiting for a task. This value could be greater than the number returned by get_max_threads() if change_max_threads() has recently been called with a negative number but not enough tasks have since completed to reduce the number of running threads to the new value set. This method will not throw and is thread safe.

Returns: The number of threads running in the thread pool, including those blocking waiting for a task.

Since 2.0.12

◆ is_error()

bool Cgu::Thread::TaskManager::is_error ( ) const

This will return true if a thread required by the thread pool has failed to start correctly because of memory exhaustion or because pthread has run out of other resources to start new threads, or because an internal operation has thrown std::bad_alloc. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion, and even more so where glib is used, as that terminates a program if memory cannot be obtained from the operating system, but there may be some specialized cases where the return value of this method is useful - this class does not use any glib functions which might cause such termination.) This method will not throw and is thread safe.

Since 2.0.12

◆ make_task_compose()

template<class Ret , class Func >

void Cgu::Thread::TaskManager::make_task_compose	(	Func &&	f,
		GMainContext *	context,
		std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >>	when
	)

inline

This is an abbreviated version of make_task_when_full(), which is for use when it is known that invocation of the callable object passed to this method and the move constructor (or if it has none, the copy constructor) of that object's return value do not throw anything other than std::bad_alloc, and the user is not interested in std::bad_alloc and does not need a Cgu::Releaser object for the 'when' callback (which is likely to cover the majority of uses, particularly when composing tasks using glib because glib terminates the program if it is unable to obtain memory).

From version 2.0.14, this method takes the callable object as a template parameter, and in version 2.0.13 it took it as a std::function object. In version 2.0.13 it was necessary to specify the return value of any callable object which was not a std::function object as a specific template parameter: this is not necessary from version 2.0.14, as it is deduced automatically.

This method does the same as the version of make_task_when() taking a callable object, except that this method takes that object as its first argument and the 'when' callback as its last argument in order to aid task composition, and in particular so tasks compose in user code in a visually ordered manner.

More particularly, like make_task_when_full(), this method is a wrapper which takes a callable object which returns a value, and constructs a TaskManager task which will execute that object by calling add_task() with an appropriate callback object, and causes the 'when' callback passed as an argument to this method to be executed by a glib main loop if and when the task finishes correctly - the 'when' callback is passed the callable object's return value when it is invoked. It is thread safe (any thread may call this method, including another task running on the TaskManager object). Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. See the documentation on add_task() for further information about how task execution works.

The 'when' callback will execute with G_PRIORITY_DEFAULT priority in the main loop.

Parameters

f	The callable object to be executed as a task, such as formed by a lambda expression or the result of std::bind. It should return a value (it cannot return void). It must be fully bound (that is, it must take no arguments when called). If an exception propagates from the task, the exception will be consumed and (if the thrown object's type is not Cgu::Thread::Exit) a g_critical() warning will be issued.
context	The glib main context of the main loop in which the 'when' callback is to be executed. A value 0/NULL/nullptr will cause the callback to be executed in the main program loop.
when	A callback which will be executed if and when the callable object passed to this method finishes correctly. The callback is passed that object's return value when it is invoked. If an exception propagates from the 'when' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.

Exceptions

std::bad_alloc This exception will be thrown if memory is exhausted and the system throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). See also the documentation for the get_max_tasks() method about the possibility of std::length_error being thrown. If std::bad_alloc or std::length_error is thrown, the task will not start (which also means that the 'when' callback will not execute).

Cgu::Thread::TaskError This exception will be thrown if stop_all() has previously been called. It will also be thrown if the call to add_task() made by this method tries but fails to start a new thread, or if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc or a thread has previously failed to start correctly. If this exception is thrown, the task will not start (which also means that the 'when' callback will not execute).

Note: 1. This method will also throw if the copy or move constructor of the callable object throws. If such an exception is thrown, the task will not start (which also means that the 'when' callback will not execute).; 2. If the callable object passed as an argument has both const and non-const operator()() methods, the non-const version will be called even if the callable object passed is a const object.; 3. If the library is compiled using the --with-auto-ptr configuration option, then this method uses std::auto_ptr in place of std::unique_ptr in its signature in order to retain compatibility with the 1.2 series of the library.; 4. As mentioned in describing 'f' above, if 'f' exits by throwing an exception the exception will be consumed and (if the thrown object's type is not Cgu::Thread::Exit) a g_critical() warning will be issued. The same will occur if the move constructor (or if it has none, the copy constructor) of the return value of 'f' throws or if the internal implementation of this wrapper throws std::bad_alloc on executing 'f'.

Since 2.0.13

◆ make_task_result() [1/4]

template<class Ret , class... Params, class... Args, class T >

Cgu::SharedLockPtr<Cgu::AsyncResult<Ret> > Cgu::Thread::TaskManager::make_task_result	(	const T &	t,
		Ret(T::*)(Params...) const	func,
		Args &&...	args
	)

This is a wrapper which takes a member function pointer to a member function which returns a value, together with arguments, and constructs a TaskManager task which will execute that function by calling add_task() with an appropriate callback object, and returns a Cgu::AsyncResult object (held by Cgu::SharedLockPtr) which will provide the value that the function returns. Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. It is thread safe: any thread may call this method, including another task running on the TaskManager object, but see the introductory remarks about the use of the TaskManager::IncHandle scoped handle class where a task running on a TaskManager object is to block on one of its sub-tasks. See also the documentation on add_task() for further information about how task execution works.

This method can take up to three bound arguments for the target member function.

If the function passed to this method exits by throwing Thread::Exit or some other exception, then the exception will be consumed and the returned Cgu::AsyncResult object's get() or move_get() method will unblock and its get_error() method will return -1.

Parameters

t	The object whose member function passed to this method is to execute as a task.
func	The member function to be executed as a task.
args	The arguments to be passed to that member function.

Exceptions

std::bad_alloc This exception will be thrown if memory is exhausted and the system throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). See also the documentation for the get_max_tasks() method about the possibility of std::length_error being thrown. If std::bad_alloc or std::length_error is thrown, the task will not start.

Cgu::Thread::TaskError This exception will be thrown if stop_all() has previously been called. It will also be thrown if the call to add_task() made by this method tries but fails to start a new thread, or if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc or a thread has previously failed to start correctly. If this exception is thrown, the task will not start.

Note: This method will also throw if the copy or move constructor of a bound argument throws. If such an exception is thrown, the task will not start.

Since 2.0.13

◆ make_task_result() [2/4]

template<class Ret , class Func >

Cgu::SharedLockPtr<Cgu::AsyncResult<Ret> > Cgu::Thread::TaskManager::make_task_result ( Func && f )

This is a wrapper which takes a callable object which returns a value (such as a std::function object, a lambda or the return value of std::bind), and constructs a TaskManager task which will execute that object by calling add_task() with an appropriate callback object, and returns a Cgu::AsyncResult object (held by Cgu::SharedLockPtr) which will provide the value that it returns. Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. It is thread safe: any thread may call this method, including another task running on the TaskManager object, but see the introductory remarks about the use of the TaskManager::IncHandle scoped handle class where a task running on a TaskManager object is to block on one of its sub-tasks. See also the documentation on add_task() for further information about how task execution works.

From version 2.0.14, this method takes the callable object as a template parameter, and in version 2.0.13 it took it as a std::function object. In version 2.0.13 it was necessary to specify the return value of any callable object which was not a std::function object as a specific template parameter: this is not necessary from version 2.0.14, as it is deduced automatically.

If the callable object passed to this method exits by throwing Thread::Exit or some other exception, then the exception will be consumed and the returned Cgu::AsyncResult object's get() or move_get() method will unblock and its get_error() method will return -1.

Parameters

f	The callable object to be executed as a task. It should return a value (it cannot return void).

Exceptions

std::bad_alloc This exception will be thrown if memory is exhausted and the system throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). See also the documentation for the get_max_tasks() method about the possibility of std::length_error being thrown. If std::bad_alloc or std::length_error is thrown, the task will not start.

Cgu::Thread::TaskError This exception will be thrown if stop_all() has previously been called. It will also be thrown if the call to add_task() made by this method tries but fails to start a new thread, or if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc or a thread has previously failed to start correctly. If this exception is thrown, the task will not start.

Note: 1. This method will also throw if the copy or move constructor of the callable object throws. If such an exception is thrown, the task will not start.; 2. If the callable object passed as an argument has both const and non-const operator()() methods, the non-const version will be called even if the callable object passed is a const object.

Since 2.0.13

◆ make_task_result() [3/4]

template<class Ret , class... Params, class... Args>

Cgu::SharedLockPtr<Cgu::AsyncResult<Ret> > Cgu::Thread::TaskManager::make_task_result	(	Ret(*)(Params...)	func,
		Args &&...	args
	)

This is a wrapper which takes a pointer to a function which returns a value, together with arguments, and constructs a TaskManager task which will execute that function by calling add_task() with an appropriate callback object, and returns a Cgu::AsyncResult object (held by Cgu::SharedLockPtr) which will provide the value that the function returns. Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. It is thread safe: any thread may call this method, including another task running on the TaskManager object, but see the introductory remarks about the use of the TaskManager::IncHandle scoped handle class where a task running on a TaskManager object is to block on one of its sub-tasks. See also the documentation on add_task() for further information about how task execution works.

This method can take up to four bound arguments for the target function.

If the function passed to this method exits by throwing Thread::Exit or some other exception, then the exception will be consumed and the returned Cgu::AsyncResult object's get() or move_get() method will unblock and its get_error() method will return -1.

Parameters

func	The function to be executed as a task.
args	The arguments to be passed to that function.

Exceptions

std::bad_alloc This exception will be thrown if memory is exhausted and the system throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). See also the documentation for the get_max_tasks() method about the possibility of std::length_error being thrown. If std::bad_alloc or std::length_error is thrown, the task will not start.

Cgu::Thread::TaskError This exception will be thrown if stop_all() has previously been called. It will also be thrown if the call to add_task() made by this method tries but fails to start a new thread, or if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc or a thread has previously failed to start correctly. If this exception is thrown, the task will not start.

Note: This method will also throw if the copy or move constructor of a bound argument throws. If such an exception is thrown, the task will not start.

Since 2.0.13

◆ make_task_result() [4/4]

template<class Ret , class... Params, class... Args, class T >

Cgu::SharedLockPtr<Cgu::AsyncResult<Ret> > Cgu::Thread::TaskManager::make_task_result	(	T &	t,
		Ret(T::*)(Params...)	func,
		Args &&...	args
	)

This is a wrapper which takes a member function pointer to a member function which returns a value, together with arguments, and constructs a TaskManager task which will execute that function by calling add_task() with an appropriate callback object, and returns a Cgu::AsyncResult object (held by Cgu::SharedLockPtr) which will provide the value that the function returns. Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. It is thread safe: any thread may call this method, including another task running on the TaskManager object, but see the introductory remarks about the use of the TaskManager::IncHandle scoped handle class where a task running on a TaskManager object is to block on one of its sub-tasks. See also the documentation on add_task() for further information about how task execution works.

This method can take up to three bound arguments for the target member function.

If the function passed to this method exits by throwing Thread::Exit or some other exception, then the exception will be consumed and the returned Cgu::AsyncResult object's get() or move_get() method will unblock and its get_error() method will return -1.

Parameters

t	The object whose member function passed to this method is to execute as a task.
func	The member function to be executed as a task.
args	The arguments to be passed to that member function.

Exceptions

std::bad_alloc This exception will be thrown if memory is exhausted and the system throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). See also the documentation for the get_max_tasks() method about the possibility of std::length_error being thrown. If std::bad_alloc or std::length_error is thrown, the task will not start.

Cgu::Thread::TaskError This exception will be thrown if stop_all() has previously been called. It will also be thrown if the call to add_task() made by this method tries but fails to start a new thread, or if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc or a thread has previously failed to start correctly. If this exception is thrown, the task will not start.

Note: This method will also throw if the copy or move constructor of a bound argument throws. If such an exception is thrown, the task will not start.

Since 2.0.13

◆ make_task_when() [1/4]

template<class Ret , class... Params, class... Args, class T >

void Cgu::Thread::TaskManager::make_task_when	(	std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >>	when,
		GMainContext *	context,
		const T &	t,
		Ret(T::*)(Params...) const	func,
		Args &&...	args
	)

inline

This is an abbreviated version of make_task_when_full(), which is for use when it is known that invocation of the member function passed to this method, the copy constructors of any non-reference arguments of that function and the move constructor (or if it has none, the copy constructor) of that function's return value do not throw anything other than std::bad_alloc, and the user is not interested in std::bad_alloc and does not need a Cgu::Releaser object for the 'when' callback (which is likely to cover the majority of uses, particularly when composing tasks using glib because glib terminates the program if it is unable to obtain memory).

This method can take up to three bound arguments for the target member function.

Like make_task_when_full(), this method is a wrapper which takes a member function pointer to a member function which returns a value, together with arguments, and constructs a TaskManager task which will execute that function by calling add_task() with an appropriate callback object, and causes the 'when' callback passed as an argument to this method to be executed by a glib main loop if and when the task finishes correctly - the 'when' callback is passed the member function's return value when it is invoked. It is thread safe (any thread may call this method, including another task running on the TaskManager object). Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. See the documentation on add_task() for further information about how task execution works.

The 'when' callback will execute with G_PRIORITY_DEFAULT priority in the main loop.

Parameters

when	A callback which will be executed if and when the function passed to this method finishes correctly. The callback is passed that function's return value when it is invoked. If an exception propagates from the 'when' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.
context	The glib main context of the main loop in which the 'when' callback is to be executed. A value 0/NULL/nullptr will cause the callback to be executed in the main program loop.
t	The object whose member function passed to this method is to execute as a task.
func	The member function to be executed as a task. If an exception propagates from the task, the exception will be consumed and (if the thrown object's type is not Cgu::Thread::Exit) a g_critical() warning will be issued.
args	The arguments to be passed to that member function.

Exceptions

std::bad_alloc This exception will be thrown if memory is exhausted and the system throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). See also the documentation for the get_max_tasks() method about the possibility of std::length_error being thrown. If std::bad_alloc or std::length_error is thrown, the task will not start (which also means that the 'when' callback will not execute).

Cgu::Thread::TaskError This exception will be thrown if stop_all() has previously been called. It will also be thrown if the call to add_task() made by this method tries but fails to start a new thread, or if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc or a thread has previously failed to start correctly. If this exception is thrown, the task will not start (which also means that the 'when' callback will not execute).

Note: 1. This method will also throw if the copy or move constructor of a bound argument throws. If such an exception is thrown, the task will not start (which also means that the 'when' callback will not execute).; 2. If the library is compiled using the --with-auto-ptr configuration option, then this method uses std::auto_ptr in place of std::unique_ptr in its signature in order to retain compatibility with the 1.2 series of the library.; 3. As mentioned in describing 'func' above, if 'func' exits by throwing an exception the exception will be consumed and (if the thrown object's type is not Cgu::Thread::Exit) a g_critical() warning will be issued. The same will occur if the copy constructor of a non-reference argument of 'func' throws when invoking 'func' or the move constructor (or if it has none, the copy constructor) of the return value of 'func' throws, or if the internal implementation of this wrapper throws std::bad_alloc on executing 'func'.

Since 2.0.13

◆ make_task_when() [2/4]

template<class Ret , class Func >

void Cgu::Thread::TaskManager::make_task_when	(	std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >>	when,
		GMainContext *	context,
		Func &&	f
	)

inline

This is an abbreviated version of make_task_when_full(), which is for use when it is known that invocation of the callable object passed to this method and the move constructor (or if it has none, the copy constructor) of that object's return value do not throw anything other than std::bad_alloc, and the user is not interested in std::bad_alloc and does not need a Cgu::Releaser object for the 'when' callback (which is likely to cover the majority of uses, particularly when composing tasks using glib because glib terminates the program if it is unable to obtain memory).

From version 2.0.14, this method takes the callable object as a template parameter, and in version 2.0.13 it took it as a std::function object. In version 2.0.13 it was necessary to specify the return value of any callable object which was not a std::function object as a specific template parameter: this is not necessary from version 2.0.14, as it is deduced automatically.

Like make_task_when_full(), this method is a wrapper which takes a callable object which returns a value, and constructs a TaskManager task which will execute that object by calling add_task() with an appropriate callback object, and causes the 'when' callback passed as an argument to this method to be executed by a glib main loop if and when the task finishes correctly - the 'when' callback is passed the callable object's return value when it is invoked. It is thread safe (any thread may call this method, including another task running on the TaskManager object). Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. See the documentation on add_task() for further information about how task execution works.

The 'when' callback will execute with G_PRIORITY_DEFAULT priority in the main loop.

There is a similar make_task_compose() function which has the callable object to be executed as a task as its first argument and the 'when' callback as its last argument, in order to aid task composition.

Parameters

when	A callback which will be executed if and when the callable object passed to this method finishes correctly. The callback is passed that object's return value when it is invoked. If an exception propagates from the 'when' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.
context	The glib main context of the main loop in which the 'when' callback is to be executed. A value 0/NULL/nullptr will cause the callback to be executed in the main program loop.
f	The callable object to be executed as a task, such as formed by a lambda expression or the result of std::bind. It should return a value (it cannot return void). It must be fully bound (that is, it must take no arguments when called). If an exception propagates from the task, the exception will be consumed and (if the thrown object's type is not Cgu::Thread::Exit) a g_critical() warning will be issued.

Exceptions

std::bad_alloc This exception will be thrown if memory is exhausted and the system throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). See also the documentation for the get_max_tasks() method about the possibility of std::length_error being thrown. If std::bad_alloc or std::length_error is thrown, the task will not start (which also means that the 'when' callback will not execute).

Cgu::Thread::TaskError This exception will be thrown if stop_all() has previously been called. It will also be thrown if the call to add_task() made by this method tries but fails to start a new thread, or if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc or a thread has previously failed to start correctly. If this exception is thrown, the task will not start (which also means that the 'when' callback will not execute).

Note: 1. This method will also throw if the copy or move constructor of the callable object throws. If such an exception is thrown, the task will not start (which also means that the 'when' callback will not execute).; 2. If the callable object passed as an argument has both const and non-const operator()() methods, the non-const version will be called even if the callable object passed is a const object.; 3. If the library is compiled using the --with-auto-ptr configuration option, then this method uses std::auto_ptr in place of std::unique_ptr in its signature in order to retain compatibility with the 1.2 series of the library.; 4. As mentioned in describing 'f' above, if 'f' exits by throwing an exception the exception will be consumed and (if the thrown object's type is not Cgu::Thread::Exit) a g_critical() warning will be issued. The same will occur if the move constructor (or if it has none, the copy constructor) of the return value of 'f' throws or if the internal implementation of this wrapper throws std::bad_alloc on executing 'f'.

Since 2.0.13

◆ make_task_when() [3/4]

template<class Ret , class... Params, class... Args>

void Cgu::Thread::TaskManager::make_task_when	(	std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >>	when,
		GMainContext *	context,
		Ret(*)(Params...)	func,
		Args &&...	args
	)

inline

This is an abbreviated version of make_task_when_full(), which is for use when it is known that invocation of the function passed to this method, the copy constructors of any non-reference arguments of that function and the move constructor (or if it has none, the copy constructor) of that function's return value do not throw anything other than std::bad_alloc, and the user is not interested in std::bad_alloc and does not need a Cgu::Releaser object for the 'when' callback (which is likely to cover the majority of uses, particularly when composing tasks using glib because glib terminates the program if it is unable to obtain memory).

This method can take up to four bound arguments for the target function.

Like make_task_when_full(), this method is a wrapper which takes a pointer to a function which returns a value, together with arguments, and constructs a TaskManager task which will execute that function by calling add_task() with an appropriate callback object, and causes the 'when' callback passed as an argument to this method to be executed by a glib main loop if and when the task finishes correctly - the 'when' callback is passed the function's return value when it is invoked. It is thread safe (any thread may call this method, including another task running on the TaskManager object). Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. See the documentation on add_task() for further information about how task execution works.

The 'when' callback will execute with G_PRIORITY_DEFAULT priority in the main loop.

Parameters

when	A callback which will be executed if and when the function passed to this method finishes correctly. The callback is passed that function's return value when it is invoked. If an exception propagates from the 'when' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.
context	The glib main context of the main loop in which the 'when' callback is to be executed. A value 0/NULL/nullptr will cause the callback to be executed in the main program loop.
func	The function to be executed as a task. If an exception propagates from the task, the exception will be consumed and (if the thrown object's type is not Cgu::Thread::Exit) a g_critical() warning will be issued.
args	The arguments to be passed to that function.

Exceptions

std::bad_alloc This exception will be thrown if memory is exhausted and the system throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). See also the documentation for the get_max_tasks() method about the possibility of std::length_error being thrown. If std::bad_alloc or std::length_error is thrown, the task will not start (which also means that the 'when' callback will not execute).

Cgu::Thread::TaskError This exception will be thrown if stop_all() has previously been called. It will also be thrown if the call to add_task() made by this method tries but fails to start a new thread, or if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc or a thread has previously failed to start correctly. If this exception is thrown, the task will not start (which also means that the 'when' callback will not execute).

Note: 1. This method will also throw if the copy or move constructor of a bound argument throws. If such an exception is thrown, the task will not start (which also means that the 'when' callback will not execute).; 2. If the library is compiled using the --with-auto-ptr configuration option, then this method uses std::auto_ptr in place of std::unique_ptr in its signature in order to retain compatibility with the 1.2 series of the library.; 3. As mentioned in describing 'func' above, if 'func' exits by throwing an exception the exception will be consumed and (if the thrown object's type is not Cgu::Thread::Exit) a g_critical() warning will be issued. The same will occur if the copy constructor of a non-reference argument of 'func' throws when invoking 'func' or the move constructor (or if it has none, the copy constructor) of the return value of 'func' throws, or if the internal implementation of this wrapper throws std::bad_alloc on executing 'func'.

Since 2.0.13

◆ make_task_when() [4/4]

template<class Ret , class... Params, class... Args, class T >

void Cgu::Thread::TaskManager::make_task_when	(	std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >>	when,
		GMainContext *	context,
		T &	t,
		Ret(T::*)(Params...)	func,
		Args &&...	args
	)

inline

This is an abbreviated version of make_task_when_full(), which is for use when it is known that invocation of the member function passed to this method, the copy constructors of any non-reference arguments of that function and the move constructor (or if it has none, the copy constructor) of that function's return value do not throw anything other than std::bad_alloc, and the user is not interested in std::bad_alloc and does not need a Cgu::Releaser object for the 'when' callback (which is likely to cover the majority of uses, particularly when composing tasks using glib because glib terminates the program if it is unable to obtain memory).

This method can take up to three bound arguments for the target member function.

Like make_task_when_full(), this method is a wrapper which takes a member function pointer to a member function which returns a value, together with arguments, and constructs a TaskManager task which will execute that function by calling add_task() with an appropriate callback object, and causes the 'when' callback passed as an argument to this method to be executed by a glib main loop if and when the task finishes correctly - the 'when' callback is passed the member function's return value when it is invoked. It is thread safe (any thread may call this method, including another task running on the TaskManager object). Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. See the documentation on add_task() for further information about how task execution works.

The 'when' callback will execute with G_PRIORITY_DEFAULT priority in the main loop.

Parameters

when	A callback which will be executed if and when the function passed to this method finishes correctly. The callback is passed that function's return value when it is invoked. If an exception propagates from the 'when' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.
context	The glib main context of the main loop in which the 'when' callback is to be executed. A value 0/NULL/nullptr will cause the callback to be executed in the main program loop.
t	The object whose member function passed to this method is to execute as a task.
func	The member function to be executed as a task. If an exception propagates from the task, the exception will be consumed and (if the thrown object's type is not Cgu::Thread::Exit) a g_critical() warning will be issued.
args	The arguments to be passed to that member function.

Exceptions

std::bad_alloc This exception will be thrown if memory is exhausted and the system throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). See also the documentation for the get_max_tasks() method about the possibility of std::length_error being thrown. If std::bad_alloc or std::length_error is thrown, the task will not start (which also means that the 'when' callback will not execute).

Cgu::Thread::TaskError This exception will be thrown if stop_all() has previously been called. It will also be thrown if the call to add_task() made by this method tries but fails to start a new thread, or if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc or a thread has previously failed to start correctly. If this exception is thrown, the task will not start (which also means that the 'when' callback will not execute).

Note: 1. This method will also throw if the copy or move constructor of a bound argument throws. If such an exception is thrown, the task will not start (which also means that the 'when' callback will not execute).; 2. If the library is compiled using the --with-auto-ptr configuration option, then this method uses std::auto_ptr in place of std::unique_ptr in its signature in order to retain compatibility with the 1.2 series of the library.; 3. As mentioned in describing 'func' above, if 'func' exits by throwing an exception the exception will be consumed and (if the thrown object's type is not Cgu::Thread::Exit) a g_critical() warning will be issued. The same will occur if the copy constructor of a non-reference argument of 'func' throws when invoking 'func' or the move constructor (or if it has none, the copy constructor) of the return value of 'func' throws, or if the internal implementation of this wrapper throws std::bad_alloc on executing 'func'.

Since 2.0.13

◆ make_task_when_full() [1/4]

template<class Ret , class... Params, class... Args, class T >

void Cgu::Thread::TaskManager::make_task_when_full	(	std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >>	when,
		Cgu::Releaser *	when_releaser,
		std::unique_ptr< const Cgu::Callback::Callback >	fail,
		Cgu::Releaser *	fail_releaser,
		gint	priority,
		GMainContext *	context,
		const T &	t,
		Ret(T::*)(Params...) const	func,
		Args &&...	args
	)

This is a wrapper which takes a member function pointer to a member function which returns a value, together with arguments, and constructs a TaskManager task which will execute that function by calling add_task() with an appropriate callback object, and causes the 'when' callback passed as an argument to this method to be executed by a glib main loop if and when the task finishes correctly - the 'when' callback is passed the member function's return value when it is invoked. It is thread safe (any thread may call this method, including another task running on the TaskManager object). Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. See the documentation on add_task() for further information about how task execution works.

This method can take up to three bound arguments for the target member function.

Note that unlike add_task(), but like the 'fail' callback of Cgu::Thread::Future objects, if a fail callback is provided to this method and it executes, it will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.

Note also that if releasers are provided for the 'when' or 'fail' callbacks, these are passed by pointer and not by reference (this is so that a NULL pointer can indicate that no releaser is to be provided). If provided, a releaser will enable automatic disconnection of the 'when' or 'fail' callback, if the object having the callback function as a member is destroyed. For this to be race free, the lifetime of that object must be controlled by the thread in whose main loop the 'when' or 'fail' callback will execute.

The make_task_when() method is similar to this method but provides an abbreviated set of paramaters suitable for most cases. This method is for use where releasers or a 'fail' callback are required.

Parameters

when	A callback which will be executed if and when the function passed to this method finishes correctly. The callback is passed that function's return value when it is invoked. If an exception propagates from the 'when' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.
when_releaser	A pointer to a Releaser object for automatic disconnection of the 'when' callback before it executes in a main loop (mainly relevant if the callback represents a non-static member function of an object which may be destroyed before the callback executes). A value of 0/NULL/nullptr indicates no releaser.
fail	A callback which will be executed if the 'when' callback does not execute. This would happen if the function passed to this method exits by throwing Thread::Exit or some other exception, if the copy constructor of a non-reference argument of that function throws, if the move constructor (or if it has none, the copy constructor) of that function's return value throws or if the 'when' callback does not execute because the internal implementation of this wrapper throws std::bad_alloc (which will not happen if the library has been installed using the --with-glib-memory-slices-no-compat configuration option: instead glib will terminate the program if it is unable to obtain memory from the operating system). If an exception propagates from the 'fail' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method. An empty std::unique_ptr object indicates no 'fail' callback.
fail_releaser	A pointer to a Releaser object for automatic disconnection of the 'fail' callback before it executes in a main loop (mainly relevant if the callback represents a non-static member function of an object which may be destroyed before the callback executes). A value of 0/NULL/nullptr indicates no releaser.
priority	The priority to be given in the main loop to the 'when' callback or any 'fail' callback. In ascending order of priorities, priorities are G_PRIORITY_LOW, G_PRIORITY_DEFAULT_IDLE, G_PRIORITY_HIGH_IDLE, G_PRIORITY_DEFAULT and G_PRIORITY_HIGH. This determines the order in which the callback will appear in the event list in the main loop, not the priority which the OS will adopt.
context	The glib main context of the main loop in which the 'when' callback or any 'fail' callback is to be executed. A value 0/NULL/nullptr will cause the callback to be executed in the main program loop.
t	The object whose member function passed to this method is to execute as a task.
func	The member function to be executed as a task. If an exception propagates from the task, the exception will be consumed and the 'fail' callback will execute.
args	The arguments to be passed to that member function.

Exceptions

std::bad_alloc This exception will be thrown if memory is exhausted and the system throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). See also the documentation for the get_max_tasks() method about the possibility of std::length_error being thrown. If std::bad_alloc or std::length_error is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).

Cgu::Thread::TaskError This exception will be thrown if stop_all() has previously been called. It will also be thrown if the call to add_task() made by this method tries but fails to start a new thread, or if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc or a thread has previously failed to start correctly. If this exception is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).

Note: 1. This method will also throw if the copy or move constructor of a bound argument throws. If such an exception is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).; 2. If a 'when_releaser' or a 'fail_releaser' object is provided, it is in theory possible (if memory is exhausted and the system throws in that case) that an internal SafeEmitterArg object will throw std::bad_alloc when emitting/executing the 'when' or 'fail' callback in the glib main loop, with the result that the relevant callback will not execute (instead the exception will be consumed and a g_critical() warning will be issued). This is rarely of any relevance because glib will abort the program if it is itself unable to obtain memory from the operating system. However, where it is relevant, design the program so that it is not necessary to provide a releaser object.; 3. If the library is compiled using the --with-auto-ptr configuration option, then this method uses std::auto_ptr in place of std::unique_ptr in its signature in order to retain compatibility with the 1.2 series of the library.

Since 2.0.13

◆ make_task_when_full() [2/4]

template<class Ret , class Func >

void Cgu::Thread::TaskManager::make_task_when_full	(	std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >>	when,
		Cgu::Releaser *	when_releaser,
		std::unique_ptr< const Cgu::Callback::Callback >	fail,
		Cgu::Releaser *	fail_releaser,
		gint	priority,
		GMainContext *	context,
		Func &&	func
	)

This is a wrapper which takes a callable object which returns a value (such as a std::function object, a lambda or the return value of std::bind), and constructs a TaskManager task which will execute that object by calling add_task() with an appropriate callback object, and causes the 'when' callback passed as an argument to this method to be executed by a glib main loop if and when the task finishes correctly - the 'when' callback is passed the callable object's return value when it is invoked. It is thread safe (any thread may call this method, including another task running on the TaskManager object). Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. See the documentation on add_task() for further information about how task execution works.

From version 2.0.14, this method takes the callable object as a template parameter, and in version 2.0.13 it took it as a std::function object. In version 2.0.13 it was necessary to specify the return value of any callable object which was not a std::function object as a specific template parameter: this is not necessary from version 2.0.14, as it is deduced automatically.

Note that unlike add_task(), but like the 'fail' callback of Cgu::Thread::Future objects, if a fail callback is provided to this method and it executes, it will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.

Note also that if releasers are provided for the 'when' or 'fail' callbacks, these are passed by pointer and not by reference (this is so that a NULL pointer can indicate that no releaser is to be provided). If provided, a releaser will enable automatic disconnection of the 'when' or 'fail' callback, if the object of which the releaser is a member is destroyed. For this to be race free, the lifetime of that object must be controlled by the thread in whose main loop the 'when' or 'fail' callback will execute.

The make_task_when() method is similar to this method but provides an abbreviated set of paramaters suitable for most cases. This method is for use where releasers or a 'fail' callback are required.

Parameters

when	A callback which will be executed if and when the callable object passed as 'func' to this method finishes correctly. The callback is passed that object's return value when it is invoked. If an exception propagates from the 'when' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.
when_releaser	A pointer to a Releaser object for automatic disconnection of the 'when' callback before it executes in a main loop (mainly relevant if the callback represents a non-static member function of an object which may be destroyed before the callback executes). A value of 0/NULL/nullptr indicates no releaser.
fail	A callback which will be executed if the 'when' callback does not execute. This would happen if the callable object passed as 'func' to this method exits by throwing Thread::Exit or some other exception, if the move constructor (or if it has none, the copy constructor) of that object's return value throws or if the 'when' callback does not execute because the internal implementation of this wrapper throws std::bad_alloc (which will not happen if the library has been installed using the --with-glib-memory-slices-no-compat configuration option: instead glib will terminate the program if it is unable to obtain memory from the operating system). If an exception propagates from the 'fail' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method. An empty std::unique_ptr object indicates no 'fail' callback.
fail_releaser	A pointer to a Releaser object for automatic disconnection of the 'fail' callback before it executes in a main loop (mainly relevant if the callback represents a non-static member function of an object which may be destroyed before the callback executes). A value of 0/NULL/nullptr indicates no releaser.
priority	The priority to be given in the main loop to the 'when' callback or any 'fail' callback. In ascending order of priorities, priorities are G_PRIORITY_LOW, G_PRIORITY_DEFAULT_IDLE, G_PRIORITY_HIGH_IDLE, G_PRIORITY_DEFAULT and G_PRIORITY_HIGH. This determines the order in which the callback will appear in the event list in the main loop, not the priority which the OS will adopt.
context	The glib main context of the main loop in which the 'when' callback or any 'fail' callback is to be executed. A value 0/NULL/nullptr will cause the callback to be executed in the main program loop.
func	The callable object to be executed as a task, such as formed by a lambda expression or the result of std::bind. It should return a value (it cannot return void). It must be fully bound (that is, it must take no arguments when called). If an exception propagates from the task, the exception will be consumed and the 'fail' callback will execute.

Exceptions

std::bad_alloc This exception will be thrown if memory is exhausted and the system throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). See also the documentation for the get_max_tasks() method about the possibility of std::length_error being thrown. If std::bad_alloc or std::length_error is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).

Cgu::Thread::TaskError This exception will be thrown if stop_all() has previously been called. It will also be thrown if the call to add_task() made by this method tries but fails to start a new thread, or if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc or a thread has previously failed to start correctly. If this exception is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).

Note: 1. This method will also throw if the copy or move constructor of the callable object throws. If such an exception is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).; 2. If the callable object passed as an argument has both const and non-const operator()() methods, the non-const version will be called even if the callable object passed is a const object.; 3. If a 'when_releaser' or a 'fail_releaser' object is provided, it is in theory possible (if memory is exhausted and the system throws in that case) that an internal SafeEmitterArg object will throw std::bad_alloc when emitting/executing the 'when' or 'fail' callback in the glib main loop, with the result that the relevant callback will not execute (instead the exception will be consumed and a g_critical() warning will be issued). This is rarely of any relevance because glib will abort the program if it is itself unable to obtain memory from the operating system. However, where it is relevant, design the program so that it is not necessary to provide a releaser object.; 4. If the library is compiled using the --with-auto-ptr configuration option, then this method uses std::auto_ptr in place of std::unique_ptr in its signature in order to retain compatibility with the 1.2 series of the library.

Since 2.0.13

◆ make_task_when_full() [3/4]

template<class Ret , class... Params, class... Args>

void Cgu::Thread::TaskManager::make_task_when_full	(	std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >>	when,
		Cgu::Releaser *	when_releaser,
		std::unique_ptr< const Cgu::Callback::Callback >	fail,
		Cgu::Releaser *	fail_releaser,
		gint	priority,
		GMainContext *	context,
		Ret(*)(Params...)	func,
		Args &&...	args
	)

This is a wrapper which takes a pointer to a function which returns a value, together with arguments, and constructs a TaskManager task which will execute that function by calling add_task() with an appropriate callback object, and causes the 'when' callback passed as an argument to this method to be executed by a glib main loop if and when the task finishes correctly - the 'when' callback is passed the function's return value when it is invoked. It is thread safe (any thread may call this method, including another task running on the TaskManager object). Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. See the documentation on add_task() for further information about how task execution works.

This method can take up to four bound arguments for the target function.

Note that unlike add_task(), but like the 'fail' callback of Cgu::Thread::Future objects, if a fail callback is provided to this method and it executes, it will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.

Note also that if releasers are provided for the 'when' or 'fail' callbacks, these are passed by pointer and not by reference (this is so that a NULL pointer can indicate that no releaser is to be provided). If provided, a releaser will enable automatic disconnection of the 'when' or 'fail' callback, if the object of which the releaser is a member is destroyed. For this to be race free, the lifetime of that object must be controlled by the thread in whose main loop the 'when' or 'fail' callback will execute.

The make_task_when() method is similar to this method but provides an abbreviated set of paramaters suitable for most cases. This method is for use where releasers or a 'fail' callback are required.

Parameters

when	A callback which will be executed if and when the function passed to this method finishes correctly. The callback is passed that function's return value when it is invoked. If an exception propagates from the 'when' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.
when_releaser	A pointer to a Releaser object for automatic disconnection of the 'when' callback before it executes in a main loop (mainly relevant if the callback represents a non-static member function of an object which may be destroyed before the callback executes). A value of 0/NULL/nullptr indicates no releaser.
fail	A callback which will be executed if the 'when' callback does not execute. This would happen if the function passed to this method exits by throwing Thread::Exit or some other exception, if the copy constructor of a non-reference argument of that function throws, if the move constructor (or if it has none, the copy constructor) of that function's return value throws or if the 'when' callback does not execute because the internal implementation of this wrapper throws std::bad_alloc (which will not happen if the library has been installed using the --with-glib-memory-slices-no-compat configuration option: instead glib will terminate the program if it is unable to obtain memory from the operating system). If an exception propagates from the 'fail' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method. An empty std::unique_ptr object indicates no 'fail' callback.
fail_releaser	A pointer to a Releaser object for automatic disconnection of the 'fail' callback before it executes in a main loop (mainly relevant if the callback represents a non-static member function of an object which may be destroyed before the callback executes). A value of 0/NULL/nullptr indicates no releaser.
priority	The priority to be given in the main loop to the 'when' callback or any 'fail' callback. In ascending order of priorities, priorities are G_PRIORITY_LOW, G_PRIORITY_DEFAULT_IDLE, G_PRIORITY_HIGH_IDLE, G_PRIORITY_DEFAULT and G_PRIORITY_HIGH. This determines the order in which the callback will appear in the event list in the main loop, not the priority which the OS will adopt.
context	The glib main context of the main loop in which the 'when' callback or any 'fail' callback is to be executed. A value 0/NULL/nullptr will cause the callback to be executed in the main program loop.
func	The function to be executed as a task. If an exception propagates from the task, the exception will be consumed and the 'fail' callback will execute.
args	The arguments to be passed to that function.

Exceptions

std::bad_alloc This exception will be thrown if memory is exhausted and the system throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). See also the documentation for the get_max_tasks() method about the possibility of std::length_error being thrown. If std::bad_alloc or std::length_error If this exception is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).

Cgu::Thread::TaskError This exception will be thrown if stop_all() has previously been called. It will also be thrown if the call to add_task() made by this method tries but fails to start a new thread, or if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc or a thread has previously failed to start correctly. If this exception is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).

Note: 1. This method will also throw if the copy or move constructor of a bound argument throws. If such an exception is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).; 2. If a 'when_releaser' or a 'fail_releaser' object is provided, it is in theory possible (if memory is exhausted and the system throws in that case) that an internal SafeEmitterArg object will throw std::bad_alloc when emitting/executing the 'when' or 'fail' callback in the glib main loop, with the result that the relevant callback will not execute (instead the exception will be consumed and a g_critical() warning will be issued). This is rarely of any relevance because glib will abort the program if it is itself unable to obtain memory from the operating system. However, where it is relevant, design the program so that it is not necessary to provide a releaser object.; 3. If the library is compiled using the --with-auto-ptr configuration option, then this method uses std::auto_ptr in place of std::unique_ptr in its signature in order to retain compatibility with the 1.2 series of the library.

Since 2.0.13

◆ make_task_when_full() [4/4]

template<class Ret , class... Params, class... Args, class T >

void Cgu::Thread::TaskManager::make_task_when_full	(	std::unique_ptr< const Cgu::Callback::CallbackArg< const Ret & >>	when,
		Cgu::Releaser *	when_releaser,
		std::unique_ptr< const Cgu::Callback::Callback >	fail,
		Cgu::Releaser *	fail_releaser,
		gint	priority,
		GMainContext *	context,
		T &	t,
		Ret(T::*)(Params...)	func,
		Args &&...	args
	)

This is a wrapper which takes a member function pointer to a member function which returns a value, together with arguments, and constructs a TaskManager task which will execute that function by calling add_task() with an appropriate callback object, and causes the 'when' callback passed as an argument to this method to be executed by a glib main loop if and when the task finishes correctly - the 'when' callback is passed the member function's return value when it is invoked. It is thread safe (any thread may call this method, including another task running on the TaskManager object). Apart from the absence of a 'one thread per task' model, this method therefore provides a similar interface to the one provided by Cgu::Thread::Future. See the documentation on add_task() for further information about how task execution works.

This method can take up to three bound arguments for the target member function.

Note that unlike add_task(), but like the 'fail' callback of Cgu::Thread::Future objects, if a fail callback is provided to this method and it executes, it will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.

Note also that if releasers are provided for the 'when' or 'fail' callbacks, these are passed by pointer and not by reference (this is so that a NULL pointer can indicate that no releaser is to be provided). If provided, a releaser will enable automatic disconnection of the 'when' or 'fail' callback, if the object having the callback function as a member is destroyed. For this to be race free, the lifetime of that object must be controlled by the thread in whose main loop the 'when' or 'fail' callback will execute.

The make_task_when() method is similar to this method but provides an abbreviated set of paramaters suitable for most cases. This method is for use where releasers or a 'fail' callback are required.

Parameters

when	A callback which will be executed if and when the function passed to this method finishes correctly. The callback is passed that function's return value when it is invoked. If an exception propagates from the 'when' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method.
when_releaser	A pointer to a Releaser object for automatic disconnection of the 'when' callback before it executes in a main loop (mainly relevant if the callback represents a non-static member function of an object which may be destroyed before the callback executes). A value of 0/NULL/nullptr indicates no releaser.
fail	A callback which will be executed if the 'when' callback does not execute. This would happen if the function passed to this method exits by throwing Thread::Exit or some other exception, if the copy constructor of a non-reference argument of that function throws, if the move constructor (or if it has none, the copy constructor) of that function's return value throws or if the 'when' callback does not execute because the internal implementation of this wrapper throws std::bad_alloc (which will not happen if the library has been installed using the --with-glib-memory-slices-no-compat configuration option: instead glib will terminate the program if it is unable to obtain memory from the operating system). If an exception propagates from the 'fail' callback, this will be consumed and a g_critical() warning will be issued. The callback will execute in the glib main loop whose GMainContext object is passed to the 'context' argument of this method. An empty std::unique_ptr object indicates no 'fail' callback.
fail_releaser	A pointer to a Releaser object for automatic disconnection of the 'fail' callback before it executes in a main loop (mainly relevant if the callback represents a non-static member function of an object which may be destroyed before the callback executes). A value of 0/NULL/nullptr indicates no releaser.
priority	The priority to be given in the main loop to the 'when' callback or any 'fail' callback. In ascending order of priorities, priorities are G_PRIORITY_LOW, G_PRIORITY_DEFAULT_IDLE, G_PRIORITY_HIGH_IDLE, G_PRIORITY_DEFAULT and G_PRIORITY_HIGH. This determines the order in which the callback will appear in the event list in the main loop, not the priority which the OS will adopt.
context	The glib main context of the main loop in which the 'when' callback or any 'fail' callback is to be executed. A value 0/NULL/nullptr will cause the callback to be executed in the main program loop.
t	The object whose member function passed to this method is to execute as a task.
func	The member function to be executed as a task. If an exception propagates from the task, the exception will be consumed and the 'fail' callback will execute.
args	The arguments to be passed to that member function.

Exceptions

std::bad_alloc This exception will be thrown if memory is exhausted and the system throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion). See also the documentation for the get_max_tasks() method about the possibility of std::length_error being thrown. If std::bad_alloc or std::length_error is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).

Cgu::Thread::TaskError This exception will be thrown if stop_all() has previously been called. It will also be thrown if the call to add_task() made by this method tries but fails to start a new thread, or if is_error() would return true because this class's internal thread pool loop implementation has thrown std::bad_alloc or a thread has previously failed to start correctly. If this exception is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).

Note: 1. This method will also throw if the copy or move constructor of a bound argument throws. If such an exception is thrown, the task will not start (which also means that the 'when' and 'fail' callbacks will not execute).; 2. If a 'when_releaser' or a 'fail_releaser' object is provided, it is in theory possible (if memory is exhausted and the system throws in that case) that an internal SafeEmitterArg object will throw std::bad_alloc when emitting/executing the 'when' or 'fail' callback in the glib main loop, with the result that the relevant callback will not execute (instead the exception will be consumed and a g_critical() warning will be issued). This is rarely of any relevance because glib will abort the program if it is itself unable to obtain memory from the operating system. However, where it is relevant, design the program so that it is not necessary to provide a releaser object.; 3. If the library is compiled using the --with-auto-ptr configuration option, then this method uses std::auto_ptr in place of std::unique_ptr in its signature in order to retain compatibility with the 1.2 series of the library.

Since 2.0.13

◆ operator=()

TaskManager& Cgu::Thread::TaskManager::operator= ( const TaskManager & )

delete

This class cannot be copied. The assignment operator is deleted.

◆ set_blocking()

void Cgu::Thread::TaskManager::set_blocking ( bool blocking )

Sets the current blocking setting, which determines whether calls to stop_all() and the destructor will block waiting for all remaining tasks to complete. This method cannot be called after stop_all() has been called (if that is attempted, Cgu::Thread::TaskError will be thrown). It is thread safe.

Parameters

blocking The new blocking setting.

Exceptions

Cgu::Thread::TaskError This exception will be thrown if stop_all() has previously been called.

Since 2.0.12

◆ set_idle_time()

void Cgu::Thread::TaskManager::set_idle_time ( unsigned int idle )

Sets the length of time in milliseconds that threads greater in number than the minimum and not executing any tasks will remain in existence waiting for new tasks. This will only have effect for threads in the pool which begin waiting for new tasks after this method is called. This method will not throw and is thread safe.

Parameters

idle	The length of the idle time in milliseconds during which threads will remain waiting for new tasks.

Since 2.0.12

◆ set_max_threads()

void Cgu::Thread::TaskManager::set_max_threads ( unsigned int max )

Deprecated:

DEPRECATED. Use change_max_threads() instead. This method will interfere with the intended operation of the ThreadManager::IncHandle class if one task constructs a IncHandle object and another calls this method.

Sets the maximum number of threads which the TaskManager object will currently run in the thread pool. If this is less than the current number of running threads, the number of threads actually running will only be reduced as tasks complete, or as idle timeouts expire. This method does nothing if stop_all() has previously been called. This method is thread safe.

Parameters

max	The maximum number of threads which the TaskManager object will currently run in the thread pool. This method will not set the maximum value of threads to a value less than that returned by get_min_threads(), nor to a value less than 1.

Exceptions

std::bad_alloc If this call is passed a value for 'max' which increases the maximum number of threads from its previous setting and tasks are currently queued for execution, new threads will be started for the queued tasks, so this exception may be thrown on starting the new threads if memory is exhausted and the system throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion).

Cgu::Thread::TaskError If this call is passed a value for 'max' which increases the maximum number of threads from its previous setting and tasks are currently queued for execution, new threads will be started for the queued tasks, so this exception may be thrown on starting the new threads if a thread fails to start correctly (this would mean that memory is exhausted, the pthread thread limit has been reached or pthread has run out of other resources to start new threads).

Since 2.0.12

◆ set_stop_mode()

void Cgu::Thread::TaskManager::set_stop_mode ( StopMode mode )

Sets the current StopMode setting (either Cgu::Thread::TaskManager::wait_for_running or Cgu::Thread::TaskManager::wait_for_all) executed when running stop_all() or when the destructor is called. See the documentation on stop_all() for an explanation of the setting. This method will not throw and is thread safe.

Parameters

mode	The new StopMode setting.

Since 2.0.12

◆ stop_all()

void Cgu::Thread::TaskManager::stop_all ( )

This will cause the TaskManager object to stop running tasks. The precise effect depends on the current StopMode and blocking settings. If StopMode is set to Cgu::Thread::TaskManager::wait_for_running, all queued tasks which are not yet running on a thread will be dispensed with, but any already running will be left to complete normally. If StopMode is set to Cgu::Thread::TaskManager::wait_for_all, both already running tasks and all tasks already queued will be permitted to execute and complete normally. If the blocking setting is set to true, this method will wait until all the tasks still to execute have finished before returning, and if false it will return straight away.

The StopMode setting should not be set to Cgu::Thread::TaskManager::wait_for_running if, when this method is called, another thread may be waiting on the get() or move_get() method of a Cgu::AsyncResult object returned by Cgu::Thread::TaskManager::make_task_result(), as otherwise that wait may never end - choose the Cgu::Thread::TaskManager::wait_for_all setting instead in such cases.

After this method has been called, any attempt to add further tasks with the add_task() method will fail, and add_task() will throw Cgu::Thread::TaskError.

This method is thread safe (any thread may call it) unless the blocking setting is true, in which case no task running on the TaskManager object may call this method.

Exceptions

std::bad_alloc	This exception will be thrown if memory is exhausted and the system throws in that case. (On systems with over-commit/lazy-commit combined with virtual memory (swap), it is rarely useful to check for memory exhaustion).
Cgu::Thread::TaskError	This exception will be thrown if stop_all() has previously been called, unless that previous call threw std::bad_alloc: if std::bad_alloc is thrown, this method may be called again to stop all threads, once the memory deficiency is dealt with, but no other methods of the TaskManager object should be called.

Since 2.0.12

The documentation for this class was generated from the following file:

task_manager.h

Classes

Public Types

Public Member Functions

Static Public Member Functions

Detailed Description

Rate limiting

Member Enumeration Documentation

◆ StopMode

Constructor & Destructor Documentation

◆ TaskManager() [1/2]

◆ TaskManager() [2/2]

◆ ~TaskManager()

Member Function Documentation

◆ add_task() [1/2]

◆ add_task() [2/2]

◆ change_max_threads()

◆ get_blocking()

◆ get_idle_time()

◆ get_max_tasks()

◆ get_max_threads()

◆ get_min_threads()

◆ get_stop_mode()

◆ get_tasks()

◆ get_used_threads()

◆ is_error()

◆ make_task_compose()

◆ make_task_result() [1/4]

◆ make_task_result() [2/4]

◆ make_task_result() [3/4]

◆ make_task_result() [4/4]

◆ make_task_when() [1/4]

◆ make_task_when() [2/4]

◆ make_task_when() [3/4]

◆ make_task_when() [4/4]

◆ make_task_when_full() [1/4]

◆ make_task_when_full() [2/4]

◆ make_task_when_full() [3/4]

◆ make_task_when_full() [4/4]

◆ operator=()

◆ set_blocking()

◆ set_idle_time()

◆ set_max_threads()

◆ set_stop_mode()

◆ stop_all()