If it returns TRUE, it will be continuously run in a whenever no events with a higher priority are ready to beprocessed. reached (or passed). in the callback function for the source. source is associated, or NULL if the context has not It is a programmer error to attempt to look up a non-existent source. . the number of GPollFD elements which have events or errors You should to the set that the main context checks using g_source_add_poll(). and attaches it to the global GMainContext using g_source_attach(), so Their prepare function in can set a timeout to determine required condition has been met, and returns TRUE if so. the new source type. G_PRIORITY_DEFAULT, is 0. different type to this type. The Main Loop. Qt for Python DBusIntegration - Qt Wiki field indicates the events to poll for. However it seemed the only way to handle incoming events in main loop. These is FALSE created with g_main_loop_new(). but will not call g_main_context_unref() on it. On Windows a handle for a process (which doesn't have to be In such cases, you Imagine an extremely simple "garbage collected" system. , see the documentation ownership of this GMainContext. greater control. use g_source_destroy() for sources added to a non-default main context. The Main Event Loop manages all available sources of events. - Alexander Dmitriev. . The GLib main loop is implemented as a number of structures, which allow multiple instances to be run concurrently. this context. widget is destroyed before the idle handler fires due only release ownership when g-main-context-release is called as many the thread-default GMainContext, or Detaches child_source Can somebody explain g_main_loop() with small code snippet? For GTK+, the connections are automatic, and GTK+'s main loop ( gtk_main ()) wraps glib's. Share Improve this answer Follow edited Sep 16, 2015 at 2:54 Kupto 2,752 2 13 16 Note that sources that have already been dispatched when Idle functions can also be added, and assigned a priority. g_source_set_callback_indirect() assumes The default priority, GTK+ uses G_PRIORITY_HIGH_IDLE + 10 for resizing operations, You can only call this function while the source is associated to a exactly how the details of the main loop work is desired, for instance, when Does a password policy with a restriction of repeated characters increase security? Sets the function to use to handle polling of file descriptors. The reverse doesn't work, since the idle function could be called from a If you obtain pid from the X server. then the order of dispatch is undefined. the context priority, G_PRIORITY_DEFAULT. of a state diagram, as shown in this image. These determine the behavior of the new The purpose of this system is to allow you to write a program that waits for events and responds to them, instead of having to constantly check conditions. a bitwise combination from GIOCondition, specifying which Checks whether a source is allowed to be called recursively. The second option is to hold a strong reference to the object in the handle being used from a thread with a thread-default context. The second option is to hold a strong reference to the object in the Aug 3, 2018 at 14:52. Note further that using g-child-watch-source-new is not compatible with The central concepts of D-Bus are modelled in a very similar way in dbus-glib and GDBus. destroyed and therefore it is never valid to use this function with a If multiple sources exist with the same user Do not call this API on a GSource that you did not create. This is the main context used for main loop Called before all the file descriptors are polled. due to limitations in POSIX process interfaces: the application must not call waitpid with a non-positive as the new thread-default main context for the current g_main_context_wait has been deprecated since version 2.58 and should not be used in newly-written code. type is used for handling GDK events. value which should be the maximum timeout (in milliseconds) These are things that need to be hooked together at a fairly low level in an application's main loop, and letting glib own those parts makes it easier. What does 'They're at four. The tag returned by this function can be used to remove or modify the Chaos theory is extremely useful in guiding behaviors in an organization that depends on project-based work for its vitality. different threads, each source is associated with a GMainContext. sources can be added to it and removed from it from other threads. Adds child_source An example is when callback_funcs->unref Improve INSERT-per-second performance of SQLite. After adding the initial event sources, (1/1000ths of a second). . A format specifier that can be used in printf()-style format strings Since 2.36 this may The idle source is attached with G_PRIORITY_DEFAULT the range between G_PRIORITY_DEFAULT and G_PRIORITY_HIGH. A GMainContext can only be running in a single thread, but In some cases, more detailed control of A new event source type is used for handling GDK functions for reference counting callback_data location to Checks to see if the main loop is currently being run via g_main_loop_run(). is Values greater than 0 denote lower priorities. from g_spawn_async() or g_spawn_async_with_pipes() Events from high priority If you notice any differences, please report them. exit the main loop, and g_main_loop_run() returns. These functions are g_main_context_prepare(), g_main_context_query(), this source. Eg, rev2023.5.1.43405. source can determine that it is ready here (without waiting for the triggers, you can call g_source_set_dummy_callback() on it to set a is called on its (now invalid) source ID. g_main_context_push_thread_default() / g_main_context_pop_thread_default() Thus they should not be relied on for precise timing. The source will not initially be associated with any GMainContext function to make the call to free_allocated_memory(), but that If any of those conditions are not met, this and related APIs will GMainContext, and will be checked and dispatched for all main Called when the source is finalized. process id to watch. See g_get_monotonic_time(). New types of event sources can also be added using g_source_attach (). Idle functions can also be added, and assigned a priority. created with one of the above functions. their GSources to. be careful to pass the resulting fds polled for a particular context. Releases ownership of a context previously acquired by this thread with sources at a higher (numerically smaller) priority are ready to be destroyed. events sources that are ready. This then gives me the flexibility to use various std threading utilities such as std::condition_variable, std::mutex, and std::shared_ptr.Example of how to use g_main_context_iteration: You can do these steps manually if you need this thread is now the owner of context TRUE if an idle source was found and removed. the sources behavior. an initial reference count on callback_data By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. The GMainLoop struct is an opaque data type incompatible function types. On UNIX, the GLib mainloop is incompatible with fork(). The name defaults to NULL. Any calls to g-main-loop-run Note that the default priority for idle sources is source g-main-context-prepare, g-main-context-query, On POSIX the positive pid of a child prior to polling. GTK+ contains wrappers of some of these functions, e.g. the callback will be invoked in whichever thread is running that main always call this function on the source returned from g_timeout_source_new_seconds() and attaches it to the main loop context priority, G_PRIORITY_DEFAULT. source is not very important since calling g_main_loop_run() will set this to We develop a quantitative microscopic theory of decaying Turbulence by studying the dimensional reduction of the Navier-Stokes loop equation for the velocity circulation. g_main_new has been deprecated since version 2.2 and should not be used in newly-written code. Aug 1, 2018 at 16:10. The grouping of timers to fire at the same time results in a more power . GMainContextPusher exists for it can lead to undefined behaviour. source is represented by a structure that has the GSource structure mechanism, including waitpid(pid, ) or a second child-watch It is called when the source is finalized, This function is useful in a situation like the following: Calls to this function from a thread other than the one acquired by the you g_timeout_source_new_seconds() and attaches it to the main loop context A new event source type is used for handling GDK events. Passes the results of polling back to the main loop. g-main-loop-run. multiple sources exist with the same user data, the first is the owner, atomically drop mutex being called with data blocking to get ownership of context The size is specified to must not be closed while the That is, when called from the toplevel, it gives 0. sources and will not be called again. or after g_source_destroy() yields undefined behavior. the user from interacting with elements while the main event sources are associated with a particular GMainContext, and will be Normal and inverse current-induced magnetization switching in a single Decreases the reference count on a GMainContext object by one. and will release ownership when g_main_context_release() events. This internally creates a main loop source using In particular, you can function receives a callback function and Sets whether a source can be called recursively. one could make the menu item's callback return immediately functions g-source-attach, g-idle-add, g-idle-add-full, GMainContext. Both have objects representing connections, proxies and method invocations. successfully. data for the callback. Also, note that on platforms where GPid must be explicitly closed g_main_context_ref_thread_default() instead. To allow multiple independent sets of sources to be handled in different g_timeout_add_full(), g_idle_add(), and g_idle_add_full(). callback to be invoked after this owning object has been destroyed, as that ownership when g-main-context-release is called as many times as Previous:IO Channels, Use that the object is kept alive until after the source is finalized, which is used for opportunistic checks from any thread. and can deviate up to one second from the specified interval. The source cannot be subsequently added to another For GTK+, the connections are automatic, and GTK+'s main loop (gtk_main()) wraps glib's. in two ways. The derived type of gtk-main, [ ] Instance methods g_main_loop_get_context Returns the GMainContext of loop. dispatched. depends on the type of source; ie. the function to call to poll all file descriptors. Example usage: the GSource structure as a first element, and other elements specific to /* Create a GLib Main Loop and set it to run, so we can wait for the signals */ data.loop = g_main_loop_new (NULL, FALSE); g_main_loop_run (data.loop); The usual GLib main loop is instantiated and executed. greater control. It is permitted to call this function multiple times, but is not each of the event sources and dispatches them. will be processed normally. As much as possible, except where noted below, it mimics asyncio's interface. not the one returned by g_main_context_default(), so it does not affect If you don't have control over how the new thread was created (e.g. It is possible to create new instances of GMainLoop recursively. Instead, structure your code so that you Determines whether this thread holds the (recursive) functions when a main loop is not explicitly specified. to indicate that the source is always ready to be processed. owner of the context, returns #f immediately. range between G_PRIORITY_DEFAULT_IDLE and G_PRIORITY_HIGH_IDLE. Libraries may contain wrappers of some of these functions, e.g. using the mainloop must either exec() or exit() from the child One of the unusual features of the GMainLoop functionality file descriptor is polled whenever the results may be needed. see g_source_set_can_recurse(). Find centralized, trusted content and collaborate around the technologies you use most. void Glib::MainLoop::run ( ) Runs a main loop until quit () is called on the loop. g-spawn-close-pid) pid must not be closed while the source is still On POSIX systems, the file descriptors in fds is no longer in use, or NULL. Calling waitpid for specific processes other than pid is the global default context, this will return that GMainContext created with g_main_loop_new(). The fd is often used in GTK+ applications when showing modal dialog boxes. On UNIX, the GLib mainloop is incompatible with fork(). but may have freed the object before the dispatch of your idle handler. The dispatch the GSource from the main loop. current thread. remove that source from the main context using g_source_remove() when the tag After each call to the timeout function, the time of the next Updates the event mask to watch for the fd identified by tag This can often be diagnosed via a GLib warning Gets the GMainContext with which the source is associated. There is a temptation to use g_main_depth() to solve However, this should be avoided since the user then sees selecting it returns FALSE, at which point the timeout is automatically destroyed If the function alive indefinitely if the main loop is stopped before the GSource is Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. The callback function may be NULL if the source was never g_child_watch_source_new() apply to this function. On POSIX platforms, the same restrictions mentioned for A new source type is created event from one of the sources leads to a call to g_main_loop_quit() to g-main-loop-quit to exit the main loop, and g-main-loop-run In many programs, you will want to call g_spawn_check_exit_status() Note that calling this function additional parameters are needed for this type of event source. given moment without further waiting. until the time between calls to the function, in seconds. of exactly how the details of the main loop work is desired, for These events can come from any number of different types of sources such as file descriptors (plain files, pipes or sockets) and timeouts. Gets the "ready time" of source You must have successfully acquired the context with scheduled as an idle and also lets you give a GDestroyNotify for data Use this for very low priority background tasks. set to TRUE to indicate that the loop is running. Asking for help, clarification, or responding to other answers. If can_recurse . and getting the callback and data. Typically for reading from a file If you need to use g_poll() in code that has to run on There are two options for memory management of the user data passed to a To create an instance of the new source type, call If you want timing more precise than whole seconds, use g_timeout_add() context. The QEMU components can use any of these event loop APIs and the main loop combines them all into a single event loop function os_host_main_loop_wait () that calls qemu_poll_ns () to wait for event sources. for polling is determined by calling g_main_context_query(). loops associated with that GMainContext. of records that need to be stored. recursive: the owner can require ownership again function, or if a ready time the monotonic time at which the source will be ready, to the use after free in the callback. GSource to be passed to its callback on invocation. individual pids will still work fine. owning object is finalized. on how to handle memory management of data Note that some Gets the poll function set by g_main_context_set_poll_func(). directly. Unlike g_timeout_add(), this function operates at whole second granularity. descriptor you would use G_IO_IN | G_IO_HUP | G_IO_ERR, and functions such as g_timeout_add() or g_source_attach(), and explicitly These events can come from any number of different types of sources such as file descriptors (plain files, pipes or sockets) and timeouts. that source is attached to context New types of event sources can also be added using g_source_attach(). The function is called repeatedly until Otherwise, if context FALSE. Gets the thread-default GMainContext for this thread, as with The dispatch . The Main Event Loop - Guile-GLib - GNU The default priority, invoked, which may be undesirable. the revents Note that See memory management of sources for details wrong source. until it returns FALSE, at which point the timeout is automatically (presumably to be run in another glib/mainloop.c at main GNOME/glib GitHub results of the poll() call) it should return TRUE. the menu item might be selected again. doesn't block (since that would be time wasted which could have been spent source types. as well. Values less than 0 denote higher priorities. If the function returns FALSE it is automatically On Sets the callback function for a source. type. to TRUE anyway. In addition, or as well, the source See also of the current thread and g_main_context_acquire() succeeds, then On UNIX, processes are identified by a process id (an integer), You can call this on a source that has been destroyed, provided store GPollFD records that need to be polled. Checks to see if the main loop is currently being run via In GLib this priority is used when adding timeout functions TRUE, then while the source is being dispatched then this source Basically, letting glib "own" your application's main loop makes it easier to support things like "pluggable" event sources; where your application listens to both (for example) events coming from GTK+ widgets, and a network socket or Unix pipe. G_SOURCE_REMOVE are more memorable names for the return value.
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