Sets our main struct and passes it to the parent class
Creates a new GMainLoop structure.
Increases the reference count on a GMainLoop object by one.
Returns the GMainContext of loop.
the main Gtk struct as a void*
Checks to see if the main loop is currently being run via g_main_loop_run().
Stops a GMainLoop from running. Any calls to g_main_loop_run() for the loop will return. Note that sources that have already been dispatched when g_main_loop_quit() is called will still be executed.
Runs a main loop until g_main_loop_quit() is called on the loop. If this is called for the thread of the loop's GMainContext, it will process events from the loop, otherwise it will simply wait.
Decreases the reference count on a GMainLoop object by one. If the result is zero, free the loop and free all associated memory.
Returns the currently firing source for this thread. Since 2.12
Returns the depth of the stack of calls to g_main_context_dispatch() on any GMainContext in the current thread. That is, when called from the toplevel, it gives 0. When called from within a callback from g_main_context_iteration() (or g_main_loop_run(), etc.) it returns 1. When called from within a callback to a recursive call to g_main_context_iteration(), it returns 2. And so forth.
Polls fds, as with the poll() system call, but portably. (On systems that don't have poll(), it is emulated using select().) This is used internally by GMainContext, but it can be called directly if you need to block until a file descriptor is ready, but don't want to run the full main loop. Each element of fds is a GPollFD describing a single file descriptor to poll. The fd field indicates the file descriptor, and the events field indicates the events to poll for. On return, the revents fields will be filled with the events that actually occurred. On POSIX systems, the file descriptors in fds can be any sort of file descriptor, but the situation is much more complicated on Windows. If you need to use g_poll() in code that has to run on Windows, the easiest solution is to construct all of your GPollFDs with g_io_channel_win32_make_pollfd(). Since 2.20
the main Gtk struct
The main event loop manages all the available sources of events for GLib and GTK+ applications. These events can come from any number of different types of sources such as file descriptors (plain files, pipes or sockets) and timeouts. New types of event sources can also be added using g_source_attach().
To allow multiple independent sets of sources to be handled in different threads, each source is associated with a GMainContext. A GMainContext can only be running in a single thread, but sources can be added to it and removed from it from other threads.
Each event source is assigned a priority. The default priority, G_PRIORITY_DEFAULT, is 0. Values less than 0 denote higher priorities. Values greater than 0 denote lower priorities. Events from high priority sources are always processed before events from lower priority sources.
Idle functions can also be added, and assigned a priority. These will be run whenever no events with a higher priority are ready to be processed.
The GMainLoop data type represents a main event loop. A GMainLoop is created with g_main_loop_new(). After adding the initial event sources, g_main_loop_run() is called. This continuously checks for new events from each of the event sources and dispatches them. Finally, the processing of an event from one of the sources leads to a call to g_main_loop_quit() to exit the main loop, and g_main_loop_run() returns.
It is possible to create new instances of GMainLoop recursively. This is often used in GTK+ applications when showing modal dialog boxes. Note that event sources are associated with a particular GMainContext, and will be checked and dispatched for all main loops associated with that GMainContext.
GTK+ contains wrappers of some of these functions, e.g. gtk_main(), gtk_main_quit() and gtk_events_pending().
Creating new source types
One of the unusual features of the GMainLoop functionality is that new types of event source can be created and used in addition to the builtin type of event source. A new event source type is used for handling GDK events. A new source type is created by deriving from the GSource structure. The derived type of source is represented by a structure that has the GSource structure as a first element, and other elements specific to the new source type. To create an instance of the new source type, call g_source_new() passing in the size of the derived structure and a table of functions. These GSourceFuncs determine the behavior of the new source type.
New source types basically interact with the main context in two ways. Their prepare function in GSourceFuncs can set a timeout to determine the maximum amount of time that the main loop will sleep before checking the source again. In addition, or as well, the source can add file descriptors to the set that the main context checks using g_source_add_poll().
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Customizing the main loop iteration
Single iterations of a GMainContext can be run with g_main_context_iteration(). In some cases, more detailed control of exactly how the details of the main loop work is desired, for instance, when integrating the GMainLoop with an external main loop. In such cases, you can call the component functions of g_main_context_iteration() directly. These functions are g_main_context_prepare(), g_main_context_query(), g_main_context_check() and g_main_context_dispatch().
The operation of these functions can best be seen in terms of a state diagram, as shown in Figure 1, “States of a Main Context”.
Figure 1. States of a Main Context
On Unix, the GLib mainloop is incompatible with fork(). Any program using the mainloop must either exec() or exit() from the child without returning to the mainloop.