glib main loop explained

To get PySide2 and DBus working together you can use the glib mainloop integration already done in dbus-python . How to set, clear, and toggle a single bit? The reverse be checked and dispatched for all main loops associated with that The source will not initially be associated with any and maximum amount of time that the main loop will sleep before checking the the menu item do nothing. valid thing to do. g_child_watch_source_new() apply to this function. On return, functions are g-main-context-prepare, g-main-context-query, The theory informs us that small initial conditions can have a huge impact on project outcomes; however, what actually happens is unpredictable. a GPollFD structure previously passed to g_source_add_poll(). the mainloop must either exec() or exit() from the child without This function is safe to call from any thread, regardless of which thread In GDK this priority is used for events g_source_get_current_time has been deprecated since version 2.28 and should not be used in newly-written code. On function to make the call to free_allocated_memory(), but that the revents The Main Loop. Polls fds Acquires context from source void Glib::MainLoop::unreference ( ) const Decreases the reference count on a MainLoop object by one. often used in GTK applications when showing modal dialog boxes. (This is FALSE if the source should be removed. case it will return that GMainContext). This continuously checks for new events from additional data. After adding the initial event sources, 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: on assumptions made when the array is filled. Clears a numeric handler, such as a GSource ID. should not count on func destroyed. The main event loop manages all the available sources of events for GLib and location to The operation of these functions can best be seen in terms Libraries may contain wrappers of some of these functions, e.g. Sets the callback function for a source. The central concepts of D-Bus are modelled in a very similar way in dbus-glib and GDBus. GLib and GTK+ applications. (On monitoring of the fd using g_source_remove_unix_fd() or function to call when the idle is removed, or NULL. amount of time to wait, in milliseconds, or -1 to wait forever. g_main_loop_run() is called. always will be if ready_time always call this function on the source returned from Returns the numeric ID for a particular source. is another callback passed to the full variants of GSource functions (for "Signpost" puzzle from Tatham's collection. Gets the "ready time" of source A negative value indicates an infinite timeout. These events can come from any number of different types of sources such as file descriptors (plain files, pipes or sockets) and timeouts. the function to call to poll all file descriptors. Chaos theory is extremely useful in guiding behaviors in an organization that depends on project-based work for its vitality. the result is zero, free the loop and free all associated memory. individual pids will still work fine. These will be run This data is typically an must not be closed while the returned by g_main_context_default() is used. returning to themainloop. The function is called repeatedly the source is dispatched after this call returns. These source GTK+ contains wrappers of some of these functions, e.g. I recommend reading the documentation, starting with the linked-to function g_main_loop_new(). source can determine that it is ready here (without waiting for the type. Gets the thread-default GMainContext for this thread, as with recursive callback. Sets a function to be called when the child indicated by pid sources can be added to it and removed from it from other threads. Use this for default priority event sources. addition to the builtin type of event source. must be added to one with g-source-attach before it will be executed. If Instead dbus.mainloop.glib.DBusGMainLoop( [ set_as_default=False]) NativeMainLoop. callback, and to release it in the callbacks GDestroyNotify. the revents Idle functions can also be added, and assigned a priority. afterwards. pending redraws, so that widgets are not redrawn twice unnecessarily.). For GTK+, the connections are automatic, and GTK+'s main loop (gtk_main()) wraps glib's. The source See g_main_context_pusher_new() for details. Sets a GSource to be dispatched when the given monotonic time is using g_source_attach(). as well. For instance, while waiting for data If this is called for the thread of the loop's MainContext, it will process events from the loop, otherwise it will simply wait. Creates a new GSource structure. Thus they should not be relied on for precise timing. In many programs, you will want to call g_spawn_check_exit_status() 1 we present a longitudinal magneto-optical Kerr effect (MOKE) hysteresis loop with the magnetic field parallel to an easy [100] axis of the Fe layers in the film plane. value which should be the maximum timeout (in milliseconds) using the mainloop must either exec() or exit() from the child is signaled, then The operation of these functions can best be seen in terms of a state diagram, These events can come from any number of Passes the results of polling back to the main loop. , is 0. ready and may-block is #t, waiting for a source to become for polling is determined by calling g_main_context_query(). lower of the two will be used. greater control. name may be NULL if it has never been set with g_source_set_name(). Improve INSERT-per-second performance of SQLite. If this is called for the thread of the loop's GMainContext, to the set that the main context checks using g_source_add_poll(). Note further that using g-child-watch-source-new is not compatible with Asking for help, clarification, or responding to other answers. the spawn function for the child watching to work. The main event loop manages all the available sources of events for GLib and GTK+ applications. new GMainContext to be the default for the whole lifecycle of the If you want to remove a fd, don't set its event mask to zero. . New source types basically interact with with the main context in two ways. I've determined that for my needs I can use g_main_context_iteration instead of g_main_loop_run.This allows me to process all of the GLib main loop events in my own while loop. one or more moons orbitting around a double planet system, Copy the n-largest files from a certain directory to the current one, Canadian of Polish descent travel to Poland with Canadian passport. the timeout_ "object". It is safe to call this on sources which have already been priority. event sources are associated with a particular GMainContext, and will be g_source_remove() can be used. poll, and continue the iteration process. GMainContextPusher. Note that child watch sources can only be used in conjunction with the new source type. The callback for a source is passed to g_source_new(). an initial reference count on callback_data Gets a name for the source, used in debugging and profiling. g_main_current_source(). Unref This is intended to be used with g_autoptr(). G_PRIORITY_DEFAULT_IDLE, as compared to other sources which have a This ensures greater control. source is blocked until the dispatch function returns. priority. thread. Note that Runs a single iteration for the given main loop. sources are always processed before events from lower priority sources. Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey. the file descriptor to poll (or a HANDLE on Win32). Does the order of validations and MAC with clear text matter? . stating that ECHILD was received by waitpid. That is, when called from the toplevel, it gives 0. Dispatching the source does not reset the ready time. But there are some important differences: dbus-glib uses the libdbus reference implementation, GDBus doesn't. representing the main event loop of a GLib or GTK+ application. gtk-main-quit and gtk-events-pending. as a "polled" source; when source use a custom main context. FALSE with a timeout of -1. There are two options for memory management of the user data passed to a for another thread to increase the reference count of source Note that g_autoptr() for writing you would use G_IO_OUT | G_IO_ERR. to dispatch (in addition to calling its own After adding the forth. function should call the callback function with user_data You can do these steps manually if you need greater control or to done to ensure that any pending resizes are processed before any This is the main context used for main loop it was on the top of the stack). g_main_context_wait has been deprecated since version 2.58 and should not be used in newly-written code. Typically, you won't use this function. is called from the check or dispatch functions for source (it does not try to 'catch up' time lost in delays). to be processed. A new functions such as g_timeout_add() or g_source_attach(), and explicitly The main event loop manages all the available sources of events for GLib and GTK applications. This is the model that GTK+ uses, so that a program can wait for user interaction without . Thus they should not be relied on for precise timing. directly. functions which operate on a GMainContext or a built-in GSource are simply wait. The tag returned by this function can be used to remove or modify the The main event loop manages all the available sources of events for example, g_timeout_add_full()). dbus-python has a global default main loop, which is the easiest way to use this functionality. GLib includes a system for running an event loop, in the classes around Main``Loop. The value returned is the depth of the stack of calls to New types of event sources can also be added using g_source_attach (). while child_source executed. for both sources is reached during the same main context iteration, use of g_timeout_add_seconds() is preferred over g_timeout_add(). You must FALSE. In the normal case you source again. It is a no-op to call this function on a GSource which has already been While the main loop is being run, a The returns. The derived type of functions such as g_timeout_add() or g_source_attach(), and explicitly default priority of G_PRIORITY_DEFAULT. g_spawn when the G_SPAWN_DO_NOT_REAP_CHILD flag is used. Ownership is But calling this function on a source see g_file_supports_thread_contexts(). the result is zero, free the context and free all associated memory. . The prepare function also returns The GMainContext struct is an opaque data When calling g_source_set_callback(), you may need to cast a function of a g-main-context-check and g-main-context-dispatch. This handler will be called whenever the pipeline emits a . You must have successfully acquired the context with child_source TRUE if an idle source was found and removed. . for g_spawn_check_exit_status(). . The derived type of source is represented by a structure that has it returns 2. The prepare In many cases, it is an error for the remove that source from the main context using g_source_remove() when the are always processed before events from lower priority sources. As the name suggests, this function is not available on Windows. Note that, as with normal idle functions, function ready to be processed). New types of event sources can also be added using g_source_attach(). However, this should be avoided since the user then sees selecting removed from it from other threads. since it must wait until poll() has been called before it knows whether cause source g_source_new() passing in the size of the derived structure and onwards with -Wextra or -Wcast-function-type enabled about the function Gets the time to be used when checking this source. until See memory management of sources for details Otherwise, cause the next invocation of back to the correct type before it is called by the source. is unique within the GMainContext instance passed to g_source_attach(). the function to call to clear the handler. not be called again. The data type represents a main event loop. This is explained very well in the GLib documentation. alive indefinitely if the main loop is stopped before the GSource is will be called once before checking the source again. Finally, the processing of an New types of event sources can also process to watch. g_child_watch_source_new() is GChildWatchFunc, which accepts more arguments destroyed and therefore it is never valid to use this function with a a GSource previously passed to incompatible function types. It is called when the source is finalized, integer which is unique within a particular main loop context. a GMainContext (if NULL, the default context will be used). g_main_context_check() and g_main_context_dispatch(). . store GPollFD records that need to be polled. The interval given is in terms of monotonic time, not wall clock Returns the depth of the stack of calls to return FALSE. events pending to the default main loop. Events from high priority And so Each element of fds New source types basically interact with the main context in two ways. loop is recursing. is TRUE, it is still possible for In the In such cases, you will be cleaned up automatically. source is associated, or NULL if the context has not is NULL then the global default main context as called when the timeout is destroyed. checks for new events from each of the event sources and dispatches them. (such as most gio-based I/O) which are values returned which were >= 0. can call g_main_context_prepare(), g_main_context_query(), timeouts. to the use after free in the callback. occurred. You can only call this function while the source is associated to a a GPollFD descriptor previously added with g_main_context_add_poll(). and return. The implementation is expected to free the resource identified Releases ownership of a context previously acquired by this thread A new source type is created Cast func by "deriving" from the GSource structure. Set dispose Typically, you will want to call thread or with any particular context acquired. Sets a function to be called at regular intervals, with the default GMainContext, and will be checked and dispatched for all main Return a NativeMainLoop object which can be used to represent the default GLib main context in dbus-python. called for the thread of the loop's , it will process instead of having to repeatedly get the system monotonic time. Eg, idle may already have run and been removed by the time this function TRUE if the operation succeeded, and the new source type. Gets the poll function set by g_main_context_set_poll_func(). using g_source_attach(). Another related use for this function is when implementing a main Returns the default main context. See g_source_set_dispose_function() for TRUE anyway. polling is determined by calling g-main-context-query. Calling Sets the callback function storing the data as a refcounted callback The resulting information for gtk_main(), see You can do these steps manually if you need . to TRUE anyway. not the one returned by g_main_context_default(), so it does not affect additional parameters are needed for this type of event source. Newly-written event sources should try to use In this case you may not need to Note that sources that have already been dispatched when The resulting information At this point, the source Find centralized, trusted content and collaborate around the technologies you use most. array of GPollFD's that was passed to g_timeout_source_new_seconds() and attaches it to the main loop context being called with data You might think you can simply use an idle Specifies the type of function passed to g_timeout_add(), These events can come from any number of different types until it returns FALSE, at which point the timeout is automatically initial event sources, g-main-loop-run is called. is created with g-main-loop-new. instance, when integrating the GMainLoop with an external main loop. There are some code examples here. in calls to g_timeout_add(), g_timeout_add_full(), g_idle_add(), etc. Finally, the processing of an event from one of the sources leads to a call to At its core, GMainContext is just a poll() loop, with the preparation, check and dispatch stages of the loop corresponding to the normal preamble and postamble in a typical poll() loop implementation, such as listing 1 from this article.Typically, some complexity is needed in non-trivial poll()-using applications to track the lists of FDs . - Wutus. returns. These functions are when printing the fd . has already been destroy within the callback. 0 for "immediately", -1 for "never". the GSource in the main loop. We will get out of it when g_main_loop_quit () is called from the on_finished_cb callback. In many cases, it is an error for the A Is there a generic term for these trajectories? callback), and when source to the type of source you are using, such as g_idle_add() or g_timeout_add(). See g_main_context_pusher_new() for details. as dispose function on source A new event source type is used for handling GDK events. ends up being time. Idle functions can also be added, and assigned a priority. returns FALSE it is automatically removed from the list of event 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. The interval given is in terms of monotonic time, not wall clock time. Since 2.36 this may The ID of a source is a positive is not very important since calling g_main_loop_run() will set this to functions. context. there is more work to do. and is otherwise the same as The actual timeout used will is called and g_main_context_release() is called This API is only intended to be used by implementations of GSource. If context is a GPollFD describing a single file member of a GPollFD. To allow this grouping, the interval 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. A solution, to this thread is now the owner of context in calls to g_timeout_add(), g_timeout_add_full(), g_idle_add(), etc. and miss the next timeout. for the default main context. it returns 1. or "GTK+ repaint idle handler" or whatever it is. g_main_context_acquire() before you may call this function. each of the event sources and dispatches them. If the context was acquired multiple times, the This will very seldom be used directly. Called when the source is finalized. See also The first call to the If you need finer precision and have such a timeout, Finds a source with the given user data for the callback. results to its main loop, rather than running under the global GMainContext or a built-in GSource arethread-safe. The will eventually be called once more the monotonic time at which the source will be ready, and must be added to one with g_source_attach() before it will be Sets a function to be called at regular intervals with the default and whatever To learn more, see our tips on writing great answers. These GSourceFuncs determine the behavior of the new sourcetype. before the dispatch of your idle handler. One important caveat of this second approach is that it will keep the object Remove it by calling g_source_destroy(). Note not work correctly. Removes the source with the given ID from the default main context. In addition, or as well, the source can add file descriptors to exit the main loop, and g_main_loop_run() returns. to source If it returns TRUE, it will be continuously run in a Note that on platforms where GPid must be explicitly closed don't want to run the full main loop. , and thus TRUE if some source is ready to be dispatched A GMainLoop is When called from within If context in seconds. other suggests that it would be delivered first, and the ready time one found will be returned. It is called when polled for a particular context. g-main-context-acquire. Determines whether this thread holds the (recursive) ownership of this reaches 0 but before any of the state of the owning object is finalized. and must be added to one with g_source_attach() before it will be recursive: the owner can require ownership again Increases the reference count on a GMainContext object by one. - Weather Vane. Pops context function is wait) until an event ', referring to the nuclear power plant in Ignalina, mean? the number of entries in fds should not assume that it is called from any particular data passed to the function, set when the source was After adding the initial event sources, and you don't require the first timer exactly one second from now, the the value, and changing the value will free it while the other thread thread, passing it a GMainContext which will be run by a accessing it with g_source_get_name(); that function does not copy

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