c++-gtk-utils
Public Types | Public Member Functions | List of all members
Cgu::AsyncQueueDispatch< T, Container > Class Template Reference

A thread-safe asynchronous queue with a blocking pop() method. More...

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

Public Types

typedef Container::value_type value_type
 
typedef Container::size_type size_type
 
typedef Container container_type
 

Public Member Functions

void push (const value_type &obj)
 
void pop (value_type &obj)
 
void pop_dispatch (value_type &obj)
 
bool pop_timed_dispatch (value_type &obj, unsigned int millisec)
 
void pop ()
 
bool empty () const
 
size_type size () const
 
void swap (AsyncQueueDispatch &other)
 
AsyncQueueDispatchoperator= (const AsyncQueueDispatch &rhs)
 
 AsyncQueueDispatch ()
 
 AsyncQueueDispatch (const AsyncQueueDispatch &rhs)
 
 ~AsyncQueueDispatch ()
 

Detailed Description

template<class T, class Container = std::list<T>>
class Cgu::AsyncQueueDispatch< T, Container >

A thread-safe asynchronous queue with a blocking pop() method.

See also
AsyncQueue AsyncChannel AsyncResult

AsyncQueueDispatch is similar to the AsyncQueue class, except that it has a blocking pop_dispatch() method, which allows it to be waited on by a dedicated event/message dispatching thread for incoming work (represented by the data pushed onto the queue). In the same way, it can be used to implement thread pools, by having threads in the pool waiting on the queue. The AsyncResult class can be useful for passing results between threads in conjunction with AsyncQueueDispatch (the documentation on AsyncResult gives an example).

By default the queue uses a std::list object as its container because when adding an item to the queue all allocation can take place outside the queue object's mutex. However, for types which have low overhead copy constructors, this can be changed to, say, a std::deque object by specifying it as the second template parameter.

If the library is installed using the --with-glib-memory-slices-compat or --with-glib-memory-slices-no-compat configuration options, any AsyncQueueDispatch objects constructed on free store will be constructed in glib memory slices. This does not affect the queue container itself: to change the allocator of the C++ container, a custom allocator type can be provided when the AsyncQueueDispatch object is instantiated offering the standard allocator interface. If glib memory slices are not used or no AsyncQueueDispatch objects are constructed on free store, it is not necessary to call g_thread_init() before manipulating or using an AsyncQueueDispatch object in multiple threads, but prior to glib version 2.32 glib itself (and thus glib memory slices) are not thread safe unless that function has been called.

Member Typedef Documentation

template<class T, class Container = std::list<T>>
typedef Container Cgu::AsyncQueueDispatch< T, Container >::container_type
template<class T, class Container = std::list<T>>
typedef Container::size_type Cgu::AsyncQueueDispatch< T, Container >::size_type
template<class T, class Container = std::list<T>>
typedef Container::value_type Cgu::AsyncQueueDispatch< T, Container >::value_type

Constructor & Destructor Documentation

template<class T, class Container = std::list<T>>
Cgu::AsyncQueueDispatch< T, Container >::AsyncQueueDispatch ( )
inline
Exceptions
std::bad_allocThe default constructor might throw this exception if memory is exhausted and the system throws in that case.
Thread::MutexErrorThe default constructor might throw this exception 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.)
Thread::CondErrorThe default constructor might throw this exception 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.)
template<class T, class Container = std::list<T>>
Cgu::AsyncQueueDispatch< T, Container >::AsyncQueueDispatch ( const AsyncQueueDispatch< T, Container > &  rhs)
inline

The copy constructor is thread safe, as it locks the initializing object's mutex to obtain a consistent view of it.

Parameters
rhsThe AsyncQueue object to be copied.
Exceptions
std::bad_allocThe copy constructor of the queue's container type, and so this constructor, might throw std::bad_alloc if memory is exhausted and the system throws in that case. It will also throw if the copy constructor of the queue's container type throws any other exceptions, including if any copy or move constructor or copy or move assignment operator of a contained item throws.
Thread::MutexErrorThe copy constructor might throw Thread::MutexError if initialization 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.)
Thread::CondErrorThe copy constructor might throw this exception 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.)

Since 1.2.22

template<class T, class Container = std::list<T>>
Cgu::AsyncQueueDispatch< T, Container >::~AsyncQueueDispatch ( )
inline

The destructor does not throw unless the destructor of a contained item throws. It is thread safe (any thread may delete the AsyncQueueDispatch object). Destroying an AsyncQueueDispatch object on which another thread is currently blocked results in undefined behavior.

Member Function Documentation

template<class T, class Container = std::list<T>>
bool Cgu::AsyncQueueDispatch< T, Container >::empty ( ) const
inline
Returns
Whether the queue is empty. It will not throw assuming that the empty() method of the container type does not throw, as it will not on any sane implementation.
Note
This method is thread safe, but the return value may not be valid if another thread has pushed to or popped from the queue before the value returned by the method is acted on. It is provided as a utility, but may not be meaningful, depending on the intended usage.
template<class T, class Container = std::list<T>>
AsyncQueueDispatch& Cgu::AsyncQueueDispatch< T, Container >::operator= ( const AsyncQueueDispatch< T, Container > &  rhs)
inline

The assignment operator is strongly exception safe with the standard sequence containers (it uses copy and swap). It is also thread safe, as it safely locks both the assignor's and assignee's mutex to provide a thread-wise atomic assignment.

Parameters
rhsThe assignor.
Returns
The AsyncQueueDispatch object after assignment.
Exceptions
std::bad_allocThe copy constructor of the queue's container type, and so this assignment operator, might throw std::bad_alloc if memory is exhausted and the system throws in that case. This assignment operator will also throw if the copy constructor of the queue's container type throws any other exceptions, including if any copy or move constructor or copy or move assignment operator of a contained item throws.
Thread::MutexErrorThe assignment operator might throw Thread::MutexError if initialization of a transitional object's 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.)
Thread::CondErrorThe assignment operator might throw this exception if initialisation of a transitional object's 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
The assignee does not, by virtue of the assignment, inherit any threads waiting on the assignor. However, if prior to the assignment threads were waiting on the assignee and the assignee acquires items from the assignor as a result of the assignment, the waiting threads will unblock and extract those items.

Since 1.2.22

template<class T, class Container = std::list<T>>
void Cgu::AsyncQueueDispatch< T, Container >::pop ( value_type obj)
inline

Pops an item from the queue. This method has strong exception safety if the container is a std::deque or std::list container (the default is std::list), provided the destructor of a contained item does not throw. It is thread safe.

Parameters
objA value type reference to which the item at the front of the queue will be assigned.
Exceptions
AsyncQueuePopErrorIf the queue is empty when a pop is attempted, this method will throw AsyncQueuePopError. It might also throw if the assignment operator of the queue item might throw. In order to complete pop() operations atomically under a single lock and to retain strong exception safety, the object into which the pop()ed data is to be placed is passed as an argument by reference (this avoids a copy from a temporary object after the data has been extracted from the queue, which would occur if the item extracted were returned by value). It might also throw if the destructor of the queue item might throw (but that should never happen), or if the empty() method of the container type throws (which would not happen on any sane implementation).
template<class T, class Container = std::list<T>>
void Cgu::AsyncQueueDispatch< T, Container >::pop ( )
inline

Discards the item at the front of the queue. This method has strong exception safety if the container is a std::deque or std::list container (the default is std::list), provided the destructor of a contained item does not throw. It is thread safe.

Exceptions
AsyncQueuePopErrorIf the queue is empty when a pop is attempted, this method will throw AsyncQueuePopError. It might also throw if the destructor of the queue item might throw (but that should never happen), or if the empty() method of the container type throws (which would not happen on any sane implementation).
template<class T, class Container = std::list<T>>
void Cgu::AsyncQueueDispatch< T, Container >::pop_dispatch ( value_type obj)
inline

Pops an item from the queue. If the queue is empty, it will block until an item becomes available. If it blocks, the wait comprises a cancellation point. This method is cancellation safe if the stack unwinds on cancellation, as cancellation is blocked while the queue is being operated on after coming out of a wait. This method has strong exception safety if the container is a std::deque or std::list container (the default is std::list), provided the destructor of a contained item does not throw. It is thread safe.

Parameters
objA value type reference to which the item at the front of the queue will be assigned. This method might throw if the assignment operator of the queue item might throw. In order to complete pop() operations atomically under a single lock and to retain strong exception safety, the object into which the pop()ed data is to be placed is passed as an argument by reference (this avoids a copy from a temporary object after the data has been extracted from the queue, which would occur if the item extracted were returned by value). It might also throw if the destructor of the queue item might throw (but that should never happen), or if the empty() method of the container type throws (which would not happen on any sane implementation).
template<class T, class Container = std::list<T>>
bool Cgu::AsyncQueueDispatch< T, Container >::pop_timed_dispatch ( value_type obj,
unsigned int  millisec 
)
inline

Pops an item from the queue. If the queue is empty, it will block until an item becomes available or until the timeout expires. If it blocks, the wait comprises a cancellation point. This method is cancellation safe if the stack unwinds on cancellation, as cancellation is blocked while the queue is being operated on after coming out of a wait. This method has strong exception safety if the container is a std::deque or std::list container (the default is std::list), provided the destructor of a contained item does not throw. It is thread safe.

Parameters
objA value type reference to which the item at the front of the queue will be assigned. This method might throw if the assignment operator of the queue item might throw. In order to complete pop() operations atomically under a single lock and to retain strong exception safety, the object into which the pop()ed data is to be placed is passed as an argument by reference (this avoids a copy from a temporary object after the data has been extracted from the queue, which would occur if the item extracted were returned by value). It might also throw if the destructor of the queue item might throw (but that should never happen), or if the empty() method of the container type throws (which would not happen on any sane implementation).
millisecThe timeout interval, in milliseconds.
Returns
If the timeout expires without an item becoming available, the method will return true. If an item from the queue is extracted, it returns false.
template<class T, class Container = std::list<T>>
void Cgu::AsyncQueueDispatch< T, Container >::push ( const value_type obj)
inline

Pushes an item onto the queue. This method has strong exception safety if the container is a std::list or std::deque container (the default is std::list), except that if std::deque is used as the container under C++11 and the copy constructor, move constructor, assignment operator or move assignment operator of the queue item throws, it only gives the basic exception guarantee (and the basic guarantee is not given by std::deque under C++11 if the queue item's move constructor throws and it uses a non-default allocator which does not provide for it to be CopyInsertable). It is thread safe.

Parameters
objThe item to be pushed onto the queue.
Exceptions
std::bad_allocThe method might throw std::bad_alloc if memory is exhausted and the system throws in that case. It might also throw if the copy constructor or assignment operator of the queue item might throw (or under C++11 if its move constructor or move assignment operator throws).
template<class T, class Container = std::list<T>>
size_type Cgu::AsyncQueueDispatch< T, Container >::size ( ) const
inline
Returns
The number of items currently in the queue. It will not throw assuming that the size() method of the container type does not throw, as it will not on any sane implementation.
Note
This method is thread safe, but the return value may not be valid if another thread has pushed to or popped from the queue before the value returned by the method is acted on. It is provided as a utility, but may not be meaningful, depending on the intended usage.

Since 1.2.22

template<class T, class Container = std::list<T>>
void Cgu::AsyncQueueDispatch< T, Container >::swap ( AsyncQueueDispatch< T, Container > &  other)
inline

Swaps the contents of 'this' and 'other'. It will not throw assuming that the swap method of the container type does not throw (which the C++ standard requires not to happen with the standard sequence containers). It is thread safe and the swap is thread-wise atomic. A non-class function Cgu::swap(Cgu::AsyncQueueDispatch&, Cgu::AsyncQueueDispatch&) method is also provided which will call this method.

Parameters
otherThe object to be swapped with this one.
Note
An object swapped does not, by virtue of the swap, inherit any threads waiting on the other one. However if threads were waiting on a swapped object prior to the swap, and it acquires items by virtue of the swap, the waiting threads will unblock and extract those items.

Since 1.2.22


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