prog_present

Typedefs
typedef gboolean(*	Cgu::PresentFunc) (void *object_data, const char **instance_args)

Functions
bool	Cgu::register_prog (const char *prog_name, PresentFunc func, void *object_data=0)
int	Cgu::present_instance (const char **instance_args=0)

Detailed Description

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

The c++-gtk-utils library provides functions to make a single instance program. The functionality for a single instance is provided by gio (if glib >= 2.26 is installed) or dbus-glib, but the interface in this file comprises only two functions, register_prog() and present_instance(). register_prog() returns 'true' if it is the first program instance to run in a particular user session, otherwise 'false'. If false is returned, present_instance() is then called to bring up the program instance already running. register_prog() is passed a function to carry out the program presentation.

Typical usage would be, for example:

GtkWidget* window;
gboolean present_func(void* data, const char** args) {
  gdk_x11_window_move_to_current_desktop(gtk_widget_get_window(window));
  gtk_window_present(GTK_WINDOW(window));
  return TRUE;
}
 
using namespace Cgu;
 
int main(int argc, char* argv[]) {
  gtk_init(&argc, &argv);
  if (register_prog("my_prog", present_func)) {
    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    ... go through normal business of creating GTK program interface ...
    gtk_main();
  }
  else {
    if (!present_instance()) gdk_notify_startup_complete();
    else {
      ... carry out a dbus failure strategy, which may mean starting
      ... the program anyway with appropriate warnings to the user
      ... that there may be multiple instances running, or may mean
      ... displaying a GtkMessageDialog object to the user suggesting
      ... that the user should check that the session message bus
      ... daemon is running, and then terminating
    }
  }
  return 0;
}

NOTE

These functions are only compiled into the library if either dbus-glib >= 0.70, or glib >= 2.26 (for gio's dbus implementation), is installed. If both are installed, gio's dbus implementation is used.

Typedef Documentation

PresentFunc

typedef gboolean(* Cgu::PresentFunc) (void *object_data, const char **instance_args)

Function pointer type that present_instance() will execute via dbus and intended to cause eg the program window to show itself. It must return TRUE if successful, FALSE if not. Returning FALSE will cause present_instance() to return 2. However, generally any GDK/GTK errors encountered by the function represented by this function pointer are best reported by that function bringing up a dialog diagnostic rather than by returning FALSE (in other words, in most cases you will want to return TRUE, even if there has been a problem). It should not throw, as the dbus and dbus-glib implementation has C linkage and cannot handle exceptions.

Parameters

object_data	NULL or persistent data, as determined by the call to register_prog(). By default it is NULL.
instance_args	NULL or a NULL terminated array of strings to be passed to the PresentFunc function on a particular invocation, as determined by present_instance(). By default it is NULL.

Returns

TRUE if successful, FALSE if not and it is important to notify the caller of the problem.

Function Documentation

present_instance()

int Cgu::present_instance

(

const char **

instance_args = 0

)

present_instance() is to be called if register_prog() returns false. Returns 0 on success, 1 if there has been a dbus error or 2 if the PresentFunc callback registered by register_prog() has returned FALSE. The instance_args argument is passed to PresentFunc on this invocation, and is either NULL (the default argument), or a NULL terminated array of strings, and in most cases you won't need it so NULL is appropriate. It is a blocking call (it will wait for the PresentFunc function to complete). It does not throw.

Parameters

instance_args

NULL or a NULL terminated array of strings to be passed to the PresentFunc function on this invocation. By default it is NULL.

Returns

0 on success, 1 on failure (say, because a dbus connection could not be obtained in order to carry out program registration) or 2 if the PresentFunc callback registered by register_prog() returns FALSE.

register_prog()

bool Cgu::register_prog	(	const char *	prog_name,
		PresentFunc	func,
		void *	object_data = 0
	)

register_prog() returns 'true' if this is the first instance of the program to register itself, otherwise 'false'. false will also be returned, and an error logged, if a dbus connection cannot be obtained in order to carry out program registration (in which case the subsequent call to present_instance() will return 1, representing failure). The first argument (prog_name) can be anything that contains valid xml name characters (provided that for any one program it is always the same for that program), but it is best to pass the name of the program to be invoked. The object data argument is persistent data passed to each invocation of PresentFunc for that program while it is running, so the data passed needs to exist throughout program execution (eg, allocate it on the heap or have it in the same scope as that in which main() returns). By default a NULL value is passed. It does not throw.

Parameters

prog_name	An identifier name comprising valid xml characters.
func	A function pointer representing the function to be executed by present_instance() if the program is already running.
object_data	NULL or persistent data to be passed to each invocation of func. By default it is NULL.

Returns

'true' if this is the first instance of the program to register itself, otherwise 'false'. false will also be returned, and an error logged, if a dbus connection cannot be obtained in order to carry out program registration (in which case the subsequent call to present_instance() will return 1, representing failure).