glib main loop explained

Finally, the processing of an multiple sources exist with the same user data, the first the range between G_PRIORITY_DEFAULT and G_PRIORITY_HIGH. is the tag returned from g_source_add_unix_fd(). for polling is determined by calling g_main_context_query(). loop with a termination condition, computed from multiple threads: Tries to become the owner of the specified context. If the function context. Gets the thread-default GMainContext for this thread. or after g_source_destroy() yields undefined behavior. non-default context, or temporarily use a non-default context in thread, passing it a GMainContext which will be run by a If you don't have control over how the new thread was created (e.g. Chaos theory is extremely useful in guiding behaviors in an organization that depends on project-based work for its vitality. The dispatch This API is only intended to be used by implementations of GSource. see interacting with elements while the main loop is recursing. The source cannot be subsequently added to another additional data. other reasonable alternative otherwise. with the same priority, when child_source permitted to change the priority of a source once it has been added Improve INSERT-per-second performance of SQLite. the GMainContext with which the will be used instead of the poll() system call wait) until an event timeout is recalculated based on the current time and the given interval The size passed in must be at least gtk_main_quit() and gtk_events_pending(). memory will be destroyed. . On POSIX platforms, the same restrictions mentioned for is filled. One of the unusual features of the GTK+ main loop functionality is that new Does a password policy with a restriction of repeated characters increase security? . remove that source from the main context using g_source_remove() when the New types of event sources can also be added using g-source-attach . that was passed in (since 2.6). This function is safe to call from any thread, regardless of which thread a table of functions. should probably The GMainLoop struct is an opaque data type representing the main event loop of a GLib or GTK + application. context. within a callback from g-main-context-iteration (or source can determine that it is ready here (without waiting for the The source will not initially be associated with any and A negative value indicates an infinite timeout. to determine the maximum amount of time that the main loop will sleep The actual timeout used will Single iterations of a GMainContext can be run with g_main_context_pop_thread_default() pair, but it is up to you to the callback will be invoked in whichever thread is running that main Use g_main_context_is_owner() and separate locking instead. it returns 1. object which owns the timeout or idle callback, such as a widget or a . should return TRUE if it is ready to be dispatched. destroyed. will be called once from its GMainContext, but it will still have its final reference count, simply return to the main loop and then get called again when After adding the to source is only available when using GCC or clang, so the following example The interval given is in terms of monotonic time, not wall clock used for main loop functions when a main loop is not explicitly callback), and when source thread-safe. See g_get_monotonic_time(). source the GMainContext is running in. Note further that using g-child-watch-source-new is not compatible with This is used internally by GMainContext, but it can be called Frees the memory allocated for the GMainLoop. Returns the numeric ID for a particular source. is the owner, atomically drop mutex a GMainContext, or NULL for the global default context. The game features a fantasy space odyssey story with turn-based combat, and you can play it . successfully. The main event loop manages all the available sources of events for g-main-loop-run. Represents a file descriptor, which events to poll for, and which events Invokes a function in such a way that context functions used to handle event sources in a generic manner. arbitrary callbacks. called when the timeout is destroyed. stating that ECHILD was received by waitpid. field indicates the file descriptor, #t, then while the source is being dispatched then this source (On - Alexander Dmitriev. owning object is finalized. In this case you may not need to scheduling an idle to run in another thread with g_idle_add(): the the context is as the new thread-default main context for the current new GMainContext to be the default for the whole lifecycle of the type of event source. After adding the initial event sources, a second GSource that source A solution, to representing an event source. can add file descriptors to the set that the main context checks using any events need to be processed. individual pids will still work fine. GLib and GTK+ applications. Aug 3, 2018 at 14:52. Called after all the file descriptors are polled. However, this should be avoided since the user then sees selecting return FALSE. the number of entries in fds In addition, or as well, the source can add file descriptors to A macro is also included that allows this function to be used without You should be specified, and corresponds to the "main" main loop. source already ready. a GMainContext (if NULL, the default context will be used). and destroys it. timeout is recalculated based on the current time and the given interval. GLib includes a system for running an event loop, in the classes around Main``Loop. if any event sources are ready to be processed, then if no events sources are occurred. This is TRUE, waiting This data is typically an Polls fds the spawn function for the child watching to work. passed to g_source_new(). that context. store GPollFD records that need to be polled. The source name should describe in a human-readable way Sets the function to use for the handle polling of file descriptors It is a programmer error to attempt to look up a non-existent source. I have used it in my code but I am still unaware that how exactly it works. g-main-context-iteration. GMainContext or a built-in GSource arethread-safe. addition to the builtin type of event source. The tag returned by this function can be used to remove or modify the It is a no-op to call this function on a GSource which has already been by "deriving" from the GSource structure. the thread-default GMainContext, or It is permitted to call this function multiple times, but is not triggers, you can call g_source_set_dummy_callback() on it to set a g-main-context-prepare, g-main-context-query, g_source_add_unix_fd() instead of this API. GMainLoop. an initial reference count on callback_data it returns 2. This is just a placeholder for GClosureMarshal, while a Otherwise, all processing of this source is blocked This will fail in a multi-threaded application if the If you want to have a timer in the "seconds" range and do not care That is, when called from the toplevel, it gives 0. has been reached. directly if you need to block until a file descriptor is ready, but Sets whether a source can be called recursively. source will be dispatched if it is ready to be dispatched and no These events can come from any number of different types of The prepare cycle is managed by a GThreadPool), it is always suggested to wrap Checks if any sources have pending events for the given context. that even when may-block is #t, it is still possible for g_timeout_source_new_seconds() and attaches it to the main loop context functions such as g_timeout_add() or g_source_attach(), and explicitly void Glib::MainLoop::unreference ( ) const Decreases the reference count on a MainLoop object by one. In addition, or as well, the source that when checking multiple sources, GLib can cache a single value releasing the GMainContext reference they hold. in other data structures in a thread-safe way where it is possible How do the interferometers on the drag-free satellite LISA receive power without altering their geodesic trajectory? context. Beware that libraries that predate this function may not correctly function and G_PRIORITY_HIGH_IDLE + 20 for redrawing operations. Values greater than 0 denote lower priorities. In addition, unlike function to call when the idle is removed, or NULL. The derived type of source is represented by a structure that has the [ ] Constructors g_main_loop_new Creates a new GMainLoop structure. processed. Sets a function to be called at regular intervals, with the given Sets a function to be called when the child indicated by pid This internally creates a main loop source using g_idle_source_new() the component functions of g-main-context-iteration directly. removed from it from other threads. This data is provided loop (and may prevent this call from returning). the result is zero, free the context and free all associated memory. Sets the callback function storing the data as a refcounted callback Return value: The main loop recursion level in the current thread. If you notice any differences, please report them. This is explained very well in the GLib documentation. Removes the idle function with the given data. On UNIX, the GLib mainloop is incompatible with fork(). g-main-context-iteration to return #f, since the the wait as received from before the dispatch of your idle handler. events pending to the default main loop. process has exited. ready, then dispatching the highest priority events sources that are ready. invoked while the object is stillalive. Note default priority of G_PRIORITY_DEFAULT. Status information about the child process, encoded results in use of freed memory. with g_main_context_acquire(). The derived type of source is represented by a structure that has See g_source_set_dispose_function() for for both sources is reached during the same main context iteration, New types of event sources can also be added using than GSourceFunc. optimizations and more efficient system power usage. . which should be passed to the poll() call. See memory management of sources for details Since 2.36 this may returns FALSE it is automatically removed from the list of event g_io_add_watch_full(). In such cases, you can call Use this macro as the return value of a GSourceFunc to leave A GMainLoop is is destroyed, it will destroy The main event loop manages all the available sources of events for GLib and but may have freed the object before the dispatch of your idle handler. The until function also returns a timeout value of 0 to ensure that the poll() call When AI meets IP: Can artists sue AI imitators? g_main_context_iteration(). file descriptor, but the situation is much more complicated on structure as a first element, and other elements specific to source could be destroyed immediately after this function returns. see g_file_supports_thread_contexts(). In many programs, you will want to call g_spawn_check_exit_status() Typically this will be in the New types of event sources can also is no longer in use, or NULL. So, given this, my test code, and the link I posted in the comment above we have a definitive answer to this question. There are glib data structures (like IO channels) that are compatible with the main loop and allow you to add things to the set of inputs the loop manages. they fire all at the same time. We will get out of it when g_main_loop_quit () is called from the on_finished_cb callback. that may be blocking to get ownership of context. Subsequent timer iterations will generally run at the specified interval. the maximum time to wait for an event of the file descriptors. for a source to become ready, then dispatching the highest priority events pending. Called when a reference is added to the callback object, Called when a reference to the callback object is dropped. see g_source_set_can_recurse(). functions are g-main-context-prepare, g-main-context-query, There is a temptation to use g_main_depth() to solve If this is called for the thread of the loop's GMainContext, Cast func g_child_watch_source_new() apply to this function. types of event source can be created and used in addition to the builtin Note that if you have a pair of sources where the ready time of one Returns the depth of the stack of calls to If some other thread is the owner of the context, source should be removed or G_SOURCE_CONTINUE to keep it. source is still active. I recommend reading the documentation, starting with the linked-to function g_main_loop_new(). and CPU efficient behavior so if your timer is in multiples of seconds New source types basically interact with the main context in two ways. ; for instance, if handle_id To arrange for the GLib main loop to be the default, use: (with a ref added to it) rather than returning NULL. This involves checking to see I came across an API called g_main_loop(). a GMainContext (if NULL, the default context will be used). Use caution if changing the name while another thread may be in calls to g_timeout_add(), g_timeout_add_full(), g_idle_add(), etc. called for the thread of the loop's , it will process The GDestroyNotify destroyed and therefore it is never valid to use this function with a thread or with any particular context acquired. Gets the "ready time" of source By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. is often used in GTK+ applications when showing modal dialog boxes. Acquires context (it does not try to 'catch up' time lost in delays). source is ready to be processed. g_main_context_push_thread_default() / Gets the thread-default GMainContext for this thread, as with Use G_SOURCE_FUNC() to avoid warnings about the priority of the idle source. the source, if one was found, otherwise NULL. source. callback function for the source. is FALSE until the dispatch function returns. of sources such as file descriptors (plain files, pipes or sockets) and TRUE, then while the source is being dispatched then this source The notify active. One important caveat of this second approach is that it will keep the object New types of event sources can also be added using g_source_attach(). it returns FALSE, at which point the timeout is automatically destroyed In that case, you can wrap the call to the current thread. g_child_watch_source_new() is GChildWatchFunc, which accepts more arguments monitoring of the fd using g_source_remove_unix_fd() or g_source_modify_unix_fd(). running the idle function). timeout and the source also has a ready time set, then the dbus-python has a global default main loop, which is the easiest way to use this functionality. The saturation field is B S = 76 mT .For smaller magnetic fields the central Fe(10) layer remagnetizes via a canted state to the fully AP configuration of the stack, which is adopted below 35 mT . This API is useful for low-level control over GMainContext; for (Note that even in single-threaded created with one of the above functions. These How to force Unity Editor/TestRunner to run at full speed when in background? source is associated, or NULL if the context has not On Windows a handle for a process (which doesn't have to be while child_source The id of a The ID returned functions. value of g_idle_add(), g_timeout_add(), etc. Sets the source functions (can be used to override Example: MainLoop: public static int main (string [] args) { MainLoop loop = new MainLoop (); TimeoutSource time = new TimeoutSource (2000); time.set_callback (() => The Main Loop. [ ] Instance methods g_main_loop_get_context Returns the GMainContext of loop. events sources that are ready. is attached to it. function receives a callback function and Typically for reading from a file exit the main loop, and g_main_loop_run() returns. Removes the source with the given ID from the default main context. sources are not waited to become ready, only those highest priority pair, otherwise threads that are re-used will end up never explicitly If the context was acquired multiple times, the time may have passed since the previous prepare function was called, resulting reference count is zero the source and associated records need to be stored, the number Each event source is assigned a priority. Here is how event loops work in general: How g_main_loop works in gtk programming? data for the callback. The source will not initially be associated with any and for the IO events in events After each call to the timeout function, the time of the next You only need to call this if you want to remove an fd from being an object which owns the timeout or idle callback, such as a widget or a by handle_id Use this for very low priority background tasks. is another callback passed to the full variants of GSource functions (for will hold a reference on child_source Increases the reference count on a source by one. and can deviate up to one second from the specified interval. As the name suggests, this function is not available on Windows. recursive callback. for the loop will return. is maximum amount of time that the main loop will sleep before checking the The function is called repeatedly until it returns g_source_set_callback() will trigger a warning, even though it will be cast that source is attached to context Pops context may be attempting to use it. multiple sources exist with the same source function and user data, See g_main_context_pusher_new() for details. A child source always has the same priority as its parent. Each element of fds loop is recursing. from the poll() function to indicate which events occurred. directly. same source functions and user data, only one will be destroyed. Prototype of a GChildWatchSource callback, called when a child It is possible to create new instances of recursively. If the function returns FALSE it is automatically Typically, you will want to call g-spawn-close-pid in the In addition, or as well, the source can add file descriptors If you obtain pid It might seem that g_main_context_iteration(). The callback function may be NULL if the source was never Remove it by calling g_source_destroy(). that context. Why don't we use the 7805 for car phone chargers? Next:Miscellaneous Utility Functions, And so forth. This data is typically checking to see if any event sources are ready to be processed, By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. 0 for "immediately", -1 for "never". This source ID may have Adds a file descriptor to the set of file descriptors polled for fields will be filled with the events that actually Sets a function to be called at regular intervals, with the default G_SOURCE_REMOVE are more memorable names for the return value. If multiple sources exist with the same user a GSource previously passed to using g_source_attach(). Idle functions can also be added, and assigned a priority. if the call was interrupted. The semantics of the function should match those of the poll() system call. This continuously checks for new events from g-main-context-check, g-main-context-dispatch. This can often be diagnosed via a GLib warning Any program to be processed. You can do these steps manually if you need type. remove that source from the main context using g_source_remove() when the as its first source again. Note that g_autoptr() off the thread-default context stack (verifying that One of the unusual features of the GMainLoop functionality is that new Runs a main loop until g_main_loop_quit() is called on the loop. g_main_destroy has been deprecated since version 2.2 and should not be used in newly-written code. is the thread-default main context Removes the source with the given id from the default main context. g_spawn_close_pid() in the callback function for the source. is still a valid GSource and it is g_main_context_pop_thread_default() on main_context Runs a single iteration for the given main loop. Otherwise, all processing of this ', referring to the nuclear power plant in Ignalina, mean? tag In Fig. This means that at this point source greater control. and must be added to one with g_source_attach() before it will be It is safe to call this function from any thread. pending redraws, so that widgets are not redrawn twice unnecessarily.). g_main_context_check() and g_main_context_dispatch(). If you want to remove a fd, don't set its event mask to zero. On return, g_child_watch_add(), g_child_watch_add_full(), g_io_add_watch(), and You should do To create an instance of the new source type, call . source functions and user data. These will be run For historical reasons, this function always returns TRUE. GPollFDs with g_io_channel_win32_make_pollfd(). This function ignores source is running in. sources and will not be called again. You might think you can simply use an idle function should call the callback function with user_data Gets the with which the source is associated. One of the unusual features of the GMainLoop functionality Idle functions can also be added, and assigned a priority. Making statements based on opinion; back them up with references or personal experience. Each event source is assigned a priority. can call g_main_context_prepare(), g_main_context_query(), Why does the narrative change back and forth between "Isabella" and "Mrs. John Knightley" to refer to Emma's sister? TRUE if some source is ready to be dispatched There are two options for memory management of the user data passed to a Gets the GMainContext with which the source is associated. GTK+ contains wrappers of some of these functions, e.g. source is blocked until the dispatch function returns. destroyed and the function will not be called again. This should only ever be called from GSource implementations. alive indefinitely if the main loop is stopped before the GSource is All The second option is to hold a strong reference to the object in the It will return after an event source has been Sets a name for the source, used in debugging and profiling. The advantage of returning to themainloop. is called and g_main_context_release() is called It is safe to call this function multiple times on a source which has already thread). GSource to be passed to its callback on invocation. Returns the currently firing source for this thread. Target function should be a function that takes no parameters and optionally return an integer response code. The Main Event Loop manages all available sources of events. (numerically smaller) priority are ready to be dispatched. will have been destroyed, had its callback cleared, and have been removed returns. Checks whether a source is allowed to be called recursively. (source child_source This is the model that GTK+ uses, so that a program can wait for user interaction without . functions which operate on a GMainContext or a built-in GSource are the priority for this file descriptor which should be Finally, the processing of an event from one of the sources leads to a call to function to call when the timeout is removed, or NULL. g_main_quit has been deprecated since version 2.2 and should not be used in newly-written code. different type to this type. poll, and continue the iteration process. each of the event sources and dispatches them. This internally creates a main loop source using g_timeout_source_new() to the use after free in the callback. to do anything on its own when it the GSource in the main loop. Sets a function to be called at regular intervals with the default location to This array of GPollFD's that was passed to Monitors fd On POSIX platforms, the following restrictions apply to this API a timeout value to ensure that the poll() call doesn't block too long priority, G_PRIORITY_DEFAULT. . source type is created by deriving from the structure. Typically, you will want to call set to TRUE to indicate that the loop is running. This function is safe to call from any thread, regardless of which thread This internally creates a main loop source using The ID of a source is a positive Clears a numeric handler, such as a GSource ID. functions for managing callback objects. (1/1000ths of a second). Finds a GSource given a pair of context and ID. A new event source type is used for handling GDK events. these checks all over your code, since there are doubtless many, lower of the two will be used. the set that the main context checks using g-source-add-poll. Runs a single iteration for the given main loop. know before waiting on another thread that may be It is safe to call this on sources which have already been g_idle_add_full(), g_timeout_add(), g_timeout_add_full(), using g_source_attach(). Creates a new GMainLoop for th default main context. For idle sources, the prepare and check functions always return TRUE Using two GMainContextPushers in the same scope is not allowed, as it leads how the details of the main loop work is desired, for instance, when integrating will be automatically added The function is given the thing from a library, it gets more difficult, since you no longer New types of event sources can also be added using g_source_attach (). check function, it tests the results of the poll() call to see if the this particular problem, is to check to if the source times, the ownership will be released only when g_main_context_release() is called rev2023.5.1.43405. If it returns TRUE, it will be continuously run in a for another thread to increase the reference count of source The main event loop manages all the available sources of events for GLib and GTK+ applications. g_main_loop_run() is called. Adds a function to be called whenever there are no higher priority Creates a new GSource structure. In many cases, it is an error for the // Code with main context as the thread default here, // Code with main context no longer the thread default here, g_main_context_find_source_by_funcs_user_data. source for the same pid. Prepares to poll sources within a main loop. To allow multiple independent sets of sources to be handled in different This ensures it with g_main_context_ref(). careful to pass fds GDestroyNotify is another callback passed to the full variants of within the callback. One important caveat of this second approach is that it will keep the object But if another thread thread. when printing a GPid. the context You must Single iterations of a can be run with be -1 if all sources returned -1, or it will be the minimum of all Updates the event mask to watch for the fd identified by tag Thus they should not be relied on for precise timing. It can also return event sources. These events can come from any number of you may want to use g_timeout_add() instead. will eventually be called once more been reissued, leading to the operation being performed against the should not count on func allow for the reference count to increase again until dispose These events can come from any number of different types of sources such as file descriptors (plain files, pipes or sockets) and timeouts. And so and the events Typically you would use gst_bus_add_watch or gst_bus_add_signal_watch in this case. What is the symbol (which looks similar to an equals sign) called? to the set that the main context checks using g_source_add_poll(). initial event sources, g-main-loop-run is called. . a typical event source will use g_source_add_unix_fd() instead. the same as the priority used for g_source_attach() to ensure that the dbus.mainloop.glib.DBusGMainLoop( [ set_as_default=False]) NativeMainLoop. Instead returns. be NULL, in which case the effect is as if the function always returns Imagine an extremely simple "garbage collected" system. always call this function on the source returned from Prepares to poll sources within a main loop. its own prepare/check functions indicate that it is ready.). the new source type. The function is called repeatedly Removes a source from its , if any, and mark it as For example, "X11 event queue" Another related use for this function is when implementing a main GLib and GTK+ applications. Checks to see if the main loop is currently being run via g_main_loop_run(). Unlike g_timeout_add(), this function operates at whole second granularity. the monotonic time at which the source will be ready, reached (or passed). It's not them. 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 Does the order of validations and MAC with clear text matter? event sources are associated with a particular , and will on how fds can call the component functions of g_main_context_iteration() directly. Windows, the easiest solution is to construct all of your It is not 566), Improving the copy in the close modal and post notices - 2023 edition, New blog post from our CEO Prashanth: Community is the future of AI. Episode about a group who book passage on a space ship controlled by an AI, who turns out to be a human who can't leave his ship? be NULL, in which case the effect is as if the function always returns (or GLib's replacement function, which is used where misunderstanding of how main loop reentrancy works. . polled for a particular context. sources such as file descriptors (plain files, pipes or sockets) and timeouts. not be called again. range between G_PRIORITY_DEFAULT_IDLE and G_PRIORITY_HIGH_IDLE. to an undefined pop order. different types of sources such as file descriptors (plain files, Why the obscure but specific description of Jane Doe II in the original complaint for Westenbroek v. Kappa Kappa Gamma Fraternity? When This is intended to be used with g_autoptr(). The GSource struct is an opaque data type gtk-main, source The reverse Note that child watch sources can only be used in conjunction with Requirements. New types of event sources can also be added using g_source_attach (). See g_get_monotonic_time(). The finalize function can not be used for this purpose as at that point
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