Sets our main struct and passes it to the parent class
Creates a new GMainContext structure.
Tries to become the owner of the specified context. If some other thread is the owner of the context, returns FALSE immediately. Ownership is properly recursive: the owner can require ownership again and will release ownership when g_main_context_release() is called as many times as g_main_context_acquire(). You must be the owner of a context before you can call g_main_context_prepare(), g_main_context_query(), g_main_context_check(), g_main_context_dispatch().
Adds a file descriptor to the set of file descriptors polled for this context. This will very seldom be used directly. Instead a typical event source will use g_source_add_unix_fd() instead.
Passes the results of polling back to the main loop.
Dispatches all pending sources.
Increases the reference count on a GMainContext object by one.
Finds a source with the given source functions and user data. If multiple sources exist with the same source function and user data, the first one found will be returned.
Finds a GSource given a pair of context and ID.
Finds a source with the given user data for the callback. If multiple sources exist with the same user data, the first one found will be returned.
Get the main Gtk struct
Gets the poll function set by g_main_context_set_poll_func().
the main Gtk struct as a void*
Invokes a function in such a way that context is owned during the invocation of function. If context is NULL then the global default main context — as returned by g_main_context_default() — is used. If context is owned by the current thread, function is called directly. Otherwise, if context is the thread-default main context of the current thread and g_main_context_acquire() succeeds, then function is called and g_main_context_release() is called afterwards. In any other case, an idle source is created to call function and that source is attached to context (presumably to be run in another thread). The idle source is attached with G_PRIORITY_DEFAULT priority. If you want a different priority, use g_main_context_invoke_full(). Note that, as with normal idle functions, function should probably return FALSE. If it returns TRUE, it will be continuously run in a loop (and may prevent this call from returning). Since 2.28
Invokes a function in such a way that context is owned during the invocation of function. This function is the same as g_main_context_invoke() except that it lets you specify the priority incase function ends up being scheduled as an idle and also lets you give a GDestroyNotify for data. notify should not assume that it is called from any particular thread or with any particular context acquired. Since 2.28
Determines whether this thread holds the (recursive) ownership of this GMainContext. This is useful to know before waiting on another thread that may be blocking to get ownership of context. Since 2.10
Runs a single iteration for the given main loop. This involves checking to see if any event sources are ready to be processed, then if no events sources are ready and may_block is TRUE, waiting for a source to become ready, then dispatching the highest priority events sources that are ready. Otherwise, if may_block is FALSE sources are not waited to become ready, only those highest priority events sources will be dispatched (if any), that are ready at this given moment without further waiting. Note that even when may_block is TRUE, it is still possible for g_main_context_iteration() to return FALSE, since the wait may be interrupted for other reasons than an event source becoming ready.
Checks if any sources have pending events for the given context.
Pops context off the thread-default context stack (verifying that it was on the top of the stack). Since 2.22
Prepares to poll sources within a main loop. The resulting information for polling is determined by calling g_main_context_query().
Acquires context and sets it as the thread-default context for the current thread. This will cause certain asynchronous operations (such as most gio-based I/O) which are started in this thread to run under context and deliver their results to its main loop, rather than running under the global default context in the main thread. Note that calling this function changes the context returned by g_main_context_get_thread_default(), not the one returned by g_main_context_default(), so it does not affect the context used by functions like g_idle_add(). Normally you would call this function shortly after creating a new thread, passing it a GMainContext which will be run by a GMainLoop in that thread, to set a new default context for all async operations in that thread. (In this case, you don't need to ever call g_main_context_pop_thread_default().) In some cases however, you may want to schedule a single operation in a non-default context, or temporarily use a non-default context in the main thread. In that case, you can wrap the call to the asynchronous operation inside a g_main_context_push_thread_default() / g_main_context_pop_thread_default() pair, but it is up to you to ensure that no other asynchronous operations accidentally get started while the non-default context is active. Beware that libraries that predate this function may not correctly handle being used from a thread with a thread-default context. Eg, see g_file_supports_thread_contexts(). Since 2.22
Determines information necessary to poll this main loop.
Releases ownership of a context previously acquired by this thread with g_main_context_acquire(). If the context was acquired multiple times, the ownership will be released only when g_main_context_release() is called as many times as it was acquired.
Removes file descriptor from the set of file descriptors to be polled for a particular context.
Sets the function to use to handle polling of file descriptors. It will be used instead of the poll() system call (or GLib's replacement function, which is used where poll() isn't available). This function could possibly be used to integrate the GLib event loop with an external event loop.
Decreases the reference count on a GMainContext object by one. If the result is zero, free the context and free all associated memory.
Tries to become the owner of the specified context, as with g_main_context_acquire(). But if another thread is the owner, atomically drop mutex and wait on cond until that owner releases ownership or until cond is signaled, then try again (once) to become the owner.
If context is currently blocking in g_main_context_iteration() waiting for a source to become ready, cause it to stop blocking and return. Otherwise, cause the next invocation of g_main_context_iteration() to return without blocking. This API is useful for low-level control over GMainContext; for example, integrating it with main loop implementations such as GMainLoop. Another related use for this function is when implementing a main
Returns the global default main context. This is the main context used for main loop functions when a main loop is not explicitly specified, and corresponds to the "main" main loop. See also g_main_context_get_thread_default().
Gets the thread-default GMainContext for this thread. Asynchronous operations that want to be able to be run in contexts other than the default one should call this method or g_main_context_ref_thread_default() to get a GMainContext to add their GSources to. (Note that even in single-threaded programs applications may sometimes want to temporarily push a non-default context, so it is not safe to assume that this will always return NULL if you are running in the default thread.) If you need to hold a reference on the context, use g_main_context_ref_thread_default() instead. Since 2.22
Gets the thread-default GMainContext for this thread, as with g_main_context_get_thread_default(), but also adds a reference to it with g_main_context_ref(). In addition, unlike g_main_context_get_thread_default(), if the thread-default context is the global default context, this will return that GMainContext (with a ref added to it) rather than returning NULL. Since 2.32
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.