The Main Event Loop

The Main Event Loop — manages all available sources of events

Functions

GMainLoop * g_main_loop_new ()
GMainLoop * g_main_loop_ref ()
void g_main_loop_unref ()
void g_main_loop_run ()
void g_main_loop_quit ()
gboolean g_main_loop_is_running ()
GMainContext * g_main_loop_get_context ()
#define g_main_new()
#define g_main_destroy()
#define g_main_run()
#define g_main_quit()
#define g_main_is_running()
GMainContext * g_main_context_new ()
GMainContext * g_main_context_ref ()
void g_main_context_unref ()
GMainContext * g_main_context_default ()
gboolean g_main_context_iteration ()
#define g_main_iteration()
gboolean g_main_context_pending ()
#define g_main_pending
GSource * g_main_context_find_source_by_id ()
GSource * g_main_context_find_source_by_user_data ()
GSource * g_main_context_find_source_by_funcs_user_data ()
void g_main_context_wakeup ()
gboolean g_main_context_acquire ()
void g_main_context_release ()
gboolean g_main_context_is_owner ()
gboolean g_main_context_wait ()
gboolean g_main_context_prepare ()
gint g_main_context_query ()
gboolean g_main_context_check ()
void g_main_context_dispatch ()
void g_main_context_set_poll_func ()
GPollFunc g_main_context_get_poll_func ()
gint (*GPollFunc) ()
void g_main_context_add_poll ()
void g_main_context_remove_poll ()
gint g_main_depth ()
GSource * g_main_current_source ()
#define g_main_set_poll_func()
void g_main_context_invoke ()
void g_main_context_invoke_full ()
GMainContext * g_main_context_get_thread_default ()
GMainContext * g_main_context_ref_thread_default ()
void g_main_context_push_thread_default ()
void g_main_context_pop_thread_default ()
GSource * g_timeout_source_new ()
GSource * g_timeout_source_new_seconds ()
guint g_timeout_add ()
guint g_timeout_add_full ()
guint g_timeout_add_seconds ()
guint g_timeout_add_seconds_full ()
GSource * g_idle_source_new ()
guint g_idle_add ()
guint g_idle_add_full ()
gboolean g_idle_remove_by_data ()
void (*GChildWatchFunc) ()
GSource * g_child_watch_source_new ()
guint g_child_watch_add ()
guint g_child_watch_add_full ()
gint g_poll ()
void (*GSourceDummyMarshal) ()
GSource * g_source_new ()
GSource * g_source_ref ()
void g_source_unref ()
void g_source_set_funcs ()
guint g_source_attach ()
void g_source_destroy ()
gboolean g_source_is_destroyed ()
void g_source_set_priority ()
gint g_source_get_priority ()
void g_source_set_can_recurse ()
gboolean g_source_get_can_recurse ()
guint g_source_get_id ()
const char * g_source_get_name ()
void g_source_set_name ()
void g_source_set_name_by_id ()
GMainContext * g_source_get_context ()
void g_source_set_callback ()
gboolean (*GSourceFunc) ()
void g_source_set_callback_indirect ()
void g_source_set_ready_time ()
gint64 g_source_get_ready_time ()
gpointer g_source_add_unix_fd ()
void g_source_remove_unix_fd ()
void g_source_modify_unix_fd ()
GIOCondition g_source_query_unix_fd ()
void g_source_add_poll ()
void g_source_remove_poll ()
void g_source_add_child_source ()
void g_source_remove_child_source ()
gint64 g_source_get_time ()
void g_source_get_current_time ()
gboolean g_source_remove ()
gboolean g_source_remove_by_funcs_user_data ()
gboolean g_source_remove_by_user_data ()

Types and Values

Includes

#include <glib.h>

Description

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().

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().

State of a Main Context

The operation of these functions can best be seen in terms of a state diagram, as shown in this image.

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.

Memory management of sources

There are two options for memory management of the user data passed to a GSource to be passed to its callback on invocation. This data is provided in calls to g_timeout_add(), g_timeout_add_full(), g_idle_add(), etc. and more generally, using g_source_set_callback(). This data is typically an object which ‘owns’ the timeout or idle callback, such as a widget or a network protocol implementation. In many cases, it is an error for the callback to be invoked after this owning object has been destroyed, as that results in use of freed memory.

The first, and preferred, option is to store the source ID returned by functions such as g_timeout_add() or g_source_attach(), and explicitly remove that source from the main context using g_source_remove() when the owning object is finalized. This ensures that the callback can only be invoked while the object is still alive.

The second option is to hold a strong reference to the object in the callback, and to release it in the callback’s GDestroyNotify. This ensures that the object is kept alive until after the source is finalized, which is guaranteed to be after it is invoked for the final time. The GDestroyNotify is another callback passed to the ‘full’ variants of GSource functions (for example, g_timeout_add_full()). It is called when the source is finalized, and is designed for releasing references like this.

One important caveat of this second approach is that it will keep the object alive indefinitely if the main loop is stopped before the GSource is invoked, which may be undesirable.

Functions

g_main_loop_new ()

GMainLoop *
g_main_loop_new (GMainContext *context,
                 gboolean is_running);

Creates a new GMainLoop structure.

Parameters

context

a GMainContext (if NULL, the default context will be used).

[nullable]

is_running

set to TRUE to indicate that the loop is running. This is not very important since calling g_main_loop_run() will set this to TRUE anyway.

 

Returns

a new GMainLoop.


g_main_loop_ref ()

GMainLoop *
g_main_loop_ref (GMainLoop *loop);

Increases the reference count on a GMainLoop object by one.

Parameters

loop

a GMainLoop

 

Returns

loop


g_main_loop_unref ()

void
g_main_loop_unref (GMainLoop *loop);

Decreases the reference count on a GMainLoop object by one. If the result is zero, free the loop and free all associated memory.

Parameters

loop

a GMainLoop

 

g_main_loop_run ()

void
g_main_loop_run (GMainLoop *loop);

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.

Parameters

loop

a GMainLoop

 

g_main_loop_quit ()

void
g_main_loop_quit (GMainLoop *loop);

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.

Parameters

loop

a GMainLoop

 

g_main_loop_is_running ()

gboolean
g_main_loop_is_running (GMainLoop *loop);

Checks to see if the main loop is currently being run via g_main_loop_run().

Parameters

loop

a GMainLoop.

 

Returns

TRUE if the mainloop is currently being run.


g_main_loop_get_context ()

GMainContext *
g_main_loop_get_context (GMainLoop *loop);

Returns the GMainContext of loop .

Parameters

loop

a GMainLoop.

 

Returns

the GMainContext of loop .

[transfer none]


g_main_new()

#define             g_main_new(is_running)

g_main_new has been deprecated since version 2.2 and should not be used in newly-written code.

Use g_main_loop_new() instead

Creates a new GMainLoop for th default main context.

Parameters

is_running

set to TRUE to indicate that the loop is running. This is not very important since calling g_main_run() will set this to TRUE anyway.

 

Returns

a new GMainLoop


g_main_destroy()

#define             g_main_destroy(loop)

g_main_destroy has been deprecated since version 2.2 and should not be used in newly-written code.

Use g_main_loop_unref() instead

Frees the memory allocated for the GMainLoop.

Parameters

loop

a GMainLoop

 

g_main_run()

#define             g_main_run(loop)

g_main_run has been deprecated since version 2.2 and should not be used in newly-written code.

Use g_main_loop_run() instead

Runs a main loop until it stops running.

Parameters

loop

a GMainLoop

 

g_main_quit()

#define             g_main_quit(loop)

g_main_quit has been deprecated since version 2.2 and should not be used in newly-written code.

Use g_main_loop_quit() instead

Stops the GMainLoop. If g_main_run() was called to run the GMainLoop, it will now return.

Parameters

loop

a GMainLoop

 

g_main_is_running()

#define             g_main_is_running(loop)

g_main_is_running has been deprecated since version 2.2 and should not be used in newly-written code.

Use g_main_loop_is_running() instead

Checks if the main loop is running.

Parameters

loop

a GMainLoop

 

Returns

TRUE if the main loop is running


g_main_context_new ()

GMainContext *
g_main_context_new (void);

Creates a new GMainContext structure.

Returns

the new GMainContext


g_main_context_ref ()

GMainContext *
g_main_context_ref (GMainContext *context);

Increases the reference count on a GMainContext object by one.

Parameters

context

a GMainContext

 

Returns

the context that was passed in (since 2.6)


g_main_context_unref ()

void
g_main_context_unref (GMainContext *context);

Decreases the reference count on a GMainContext object by one. If the result is zero, free the context and free all associated memory.

Parameters

context

a GMainContext

 

g_main_context_default ()

GMainContext *
g_main_context_default (void);

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().

Returns

the global default main context.

[transfer none]


g_main_context_iteration ()

gboolean
g_main_context_iteration (GMainContext *context,
                          gboolean may_block);

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.

Parameters

context

a GMainContext (if NULL, the default context will be used).

[nullable]

may_block

whether the call may block.

 

Returns

TRUE if events were dispatched.


g_main_iteration()

#define             g_main_iteration(may_block)

g_main_iteration has been deprecated since version 2.2 and should not be used in newly-written code.

Use g_main_context_iteration() instead.

Runs a single iteration for the default GMainContext.

Parameters

may_block

set to TRUE if it should block (i.e. wait) until an event source becomes ready. It will return after an event source has been processed. If set to FALSE it will return immediately if no event source is ready to be processed.

 

Returns

TRUE if more events are pending.


g_main_context_pending ()

gboolean
g_main_context_pending (GMainContext *context);

Checks if any sources have pending events for the given context.

Parameters

context

a GMainContext (if NULL, the default context will be used).

[nullable]

Returns

TRUE if events are pending.


g_main_pending

#define             g_main_pending()

g_main_pending is deprecated and should not be used in newly-written code.

Checks if any events are pending for the default GMainContext (i.e. ready to be processed).

Returns

TRUE if any events are pending.

Deprected: 2.2: Use g_main_context_pending() instead.


g_main_context_find_source_by_id ()

GSource *
g_main_context_find_source_by_id (GMainContext *context,
                                  guint source_id);

Finds a GSource given a pair of context and ID.

It is a programmer error to attempt to lookup a non-existent source.

More specifically: source IDs can be reissued after a source has been destroyed and therefore it is never valid to use this function with a source ID which may have already been removed. An example is when scheduling an idle to run in another thread with g_idle_add(): the idle may already have run and been removed by the time this function is called on its (now invalid) source ID. This source ID may have been reissued, leading to the operation being performed against the wrong source.

Parameters

context

a GMainContext (if NULL, the default context will be used).

[nullable]

source_id

the source ID, as returned by g_source_get_id().

 

Returns

the GSource.

[transfer none]


g_main_context_find_source_by_user_data ()

GSource *
g_main_context_find_source_by_user_data
                               (GMainContext *context,
                                gpointer user_data);

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.

Parameters

context

a GMainContext

 

user_data

the user_data for the callback.

 

Returns

the source, if one was found, otherwise NULL.

[transfer none]


g_main_context_find_source_by_funcs_user_data ()

GSource *
g_main_context_find_source_by_funcs_user_data
                               (GMainContext *context,
                                GSourceFuncs *funcs,
                                gpointer user_data);

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.

Parameters

context

a GMainContext (if NULL, the default context will be used).

[nullable]

funcs

the source_funcs passed to g_source_new().

 

user_data

the user data from the callback.

 

Returns

the source, if one was found, otherwise NULL.

[transfer none]


g_main_context_wakeup ()

void
g_main_context_wakeup (GMainContext *context);

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 loop with a termination condition, computed from multiple threads:

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#define NUM_TASKS 10
static volatile gint tasks_remaining = NUM_TASKS;
...
 
while (g_atomic_int_get (&tasks_remaining) != 0)
  g_main_context_iteration (NULL, TRUE);

Then in a thread:

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perform_work();

if (g_atomic_int_dec_and_test (&tasks_remaining))
  g_main_context_wakeup (NULL);

Parameters

context

a GMainContext

 

g_main_context_acquire ()

gboolean
g_main_context_acquire (GMainContext *context);

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().

Parameters

context

a GMainContext

 

Returns

TRUE if the operation succeeded, and this thread is now the owner of context .


g_main_context_release ()

void
g_main_context_release (GMainContext *context);

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.

Parameters

context

a GMainContext

 

g_main_context_is_owner ()

gboolean
g_main_context_is_owner (GMainContext *context);

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 .

Parameters

context

a GMainContext

 

Returns

TRUE if current thread is owner of context .

Since: 2.10


g_main_context_wait ()

gboolean
g_main_context_wait (GMainContext *context,
                     GCond *cond,
                     GMutex *mutex);

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.

Parameters

context

a GMainContext

 

cond

a condition variable

 

mutex

a mutex, currently held

 

Returns

TRUE if the operation succeeded, and this thread is now the owner of context .


g_main_context_prepare ()

gboolean
g_main_context_prepare (GMainContext *context,
                        gint *priority);

Prepares to poll sources within a main loop. The resulting information for polling is determined by calling g_main_context_query().

You must have successfully acquired the context with g_main_context_acquire() before you may call this function.

Parameters

context

a GMainContext

 

priority

location to store priority of highest priority source already ready.

 

Returns

TRUE if some source is ready to be dispatched prior to polling.


g_main_context_query ()

gint
g_main_context_query (GMainContext *context,
                      gint max_priority,
                      gint *timeout_,
                      GPollFD *fds,
                      gint n_fds);

Determines information necessary to poll this main loop.

You must have successfully acquired the context with g_main_context_acquire() before you may call this function.

Parameters

context

a GMainContext

 

max_priority

maximum priority source to check

 

timeout_

location to store timeout to be used in polling.

[out]

fds

location to store GPollFD records that need to be polled.

[out caller-allocates][array length=n_fds]

n_fds

length of fds .

[in]

Returns

the number of records actually stored in fds , or, if more than n_fds records need to be stored, the number of records that need to be stored.


g_main_context_check ()

gboolean
g_main_context_check (GMainContext *context,
                      gint max_priority,
                      GPollFD *fds,
                      gint n_fds);

Passes the results of polling back to the main loop.

You must have successfully acquired the context with g_main_context_acquire() before you may call this function.

Parameters

context

a GMainContext

 

max_priority

the maximum numerical priority of sources to check

 

fds

array of GPollFD's that was passed to the last call to g_main_context_query().

[array length=n_fds]

n_fds

return value of g_main_context_query()

 

Returns

TRUE if some sources are ready to be dispatched.


g_main_context_dispatch ()

void
g_main_context_dispatch (GMainContext *context);

Dispatches all pending sources.

You must have successfully acquired the context with g_main_context_acquire() before you may call this function.

Parameters

context

a GMainContext

 

g_main_context_set_poll_func ()

void
g_main_context_set_poll_func (GMainContext *context,
                              GPollFunc func);

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.

Parameters

context

a GMainContext

 

func

the function to call to poll all file descriptors

 

g_main_context_get_poll_func ()

GPollFunc
g_main_context_get_poll_func (GMainContext *context);

Gets the poll function set by g_main_context_set_poll_func().

Parameters

context

a GMainContext

 

Returns

the poll function


GPollFunc ()

gint
(*GPollFunc) (GPollFD *ufds,
              guint nfsd,
              gint timeout_);

Specifies the type of function passed to g_main_context_set_poll_func(). The semantics of the function should match those of the poll() system call.

Parameters

ufds

an array of GPollFD elements

 

nfsd

the number of elements in ufds

 

timeout_

the maximum time to wait for an event of the file descriptors. A negative value indicates an infinite timeout.

 

Returns

the number of GPollFD elements which have events or errors reported, or -1 if an error occurred.


g_main_context_add_poll ()

void
g_main_context_add_poll (GMainContext *context,
                         GPollFD *fd,
                         gint priority);

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.

Parameters

context

a GMainContext (or NULL for the default context).

[nullable]

fd

a GPollFD structure holding information about a file descriptor to watch.

 

priority

the priority for this file descriptor which should be the same as the priority used for g_source_attach() to ensure that the file descriptor is polled whenever the results may be needed.

 

g_main_context_remove_poll ()

void
g_main_context_remove_poll (GMainContext *context,
                            GPollFD *fd);

Removes file descriptor from the set of file descriptors to be polled for a particular context.

Parameters

context

a GMainContext

 

fd

a GPollFD descriptor previously added with g_main_context_add_poll()

 

g_main_depth ()

gint
g_main_depth (void);

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.

This function is useful in a situation like the following: Imagine an extremely simple "garbage collected" system.

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static GList *free_list;

gpointer
allocate_memory (gsize size)
{ 
  gpointer result = g_malloc (size);
  free_list = g_list_prepend (free_list, result);
  return result;
}

void
free_allocated_memory (void)
{
  GList *l;
  for (l = free_list; l; l = l->next);
    g_free (l->data);
  g_list_free (free_list);
  free_list = NULL;
 }

[...]

while (TRUE); 
 {
   g_main_context_iteration (NULL, TRUE);
   free_allocated_memory();
  }

This works from an application, however, if you want to do the same thing from a library, it gets more difficult, since you no longer control the main loop. You might think you can simply use an idle function to make the call to free_allocated_memory(), but that doesn't work, since the idle function could be called from a recursive callback. This can be fixed by using g_main_depth()

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gpointer
allocate_memory (gsize size)
{ 
  FreeListBlock *block = g_new (FreeListBlock, 1);
  block->mem = g_malloc (size);
  block->depth = g_main_depth ();   
  free_list = g_list_prepend (free_list, block);
  return block->mem;
}

void
free_allocated_memory (void)
{
  GList *l;
  
  int depth = g_main_depth ();
  for (l = free_list; l; );
    {
      GList *next = l->next;
      FreeListBlock *block = l->data;
      if (block->depth > depth)
        {
          g_free (block->mem);
          g_free (block);
          free_list = g_list_delete_link (free_list, l);
        }
              
      l = next;
    }
  }

There is a temptation to use g_main_depth() to solve problems with reentrancy. For instance, while waiting for data to be received from the network in response to a menu item, the menu item might be selected again. It might seem that one could make the menu item's callback return immediately and do nothing if g_main_depth() returns a value greater than 1. However, this should be avoided since the user then sees selecting the menu item do nothing. Furthermore, you'll find yourself adding these checks all over your code, since there are doubtless many, many things that the user could do. Instead, you can use the following techniques:

  1. Use gtk_widget_set_sensitive() or modal dialogs to prevent the user from interacting with elements while the main loop is recursing.

  2. Avoid main loop recursion in situations where you can't handle arbitrary callbacks. Instead, structure your code so that you simply return to the main loop and then get called again when there is more work to do.

Returns

The main loop recursion level in the current thread


g_main_current_source ()

GSource *
g_main_current_source (void);

Returns the currently firing source for this thread.

Returns

The currently firing source or NULL.

[transfer none]

Since: 2.12


g_main_set_poll_func()

#define             g_main_set_poll_func(func)

g_main_set_poll_func has been deprecated since version 2.2 and should not be used in newly-written code.

Use g_main_context_set_poll_func() again

Sets the function to use for the handle polling of file descriptors for the default main context.

Parameters

func

the function to call to poll all file descriptors

 

g_main_context_invoke ()

void
g_main_context_invoke (GMainContext *context,
                       GSourceFunc function,
                       gpointer data);

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).

Parameters

context

a GMainContext, or NULL.

[nullable]

function

function to call

 

data

data to pass to function

 

Since: 2.28


g_main_context_invoke_full ()

void
g_main_context_invoke_full (GMainContext *context,
                            gint priority,
                            GSourceFunc function,
                            gpointer data,
                            GDestroyNotify notify);

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.

Parameters

context

a GMainContext, or NULL.

[nullable]

priority

the priority at which to run function

 

function

function to call

 

data

data to pass to function

 

notify

a function to call when data is no longer in use, or NULL.

[nullable]

Since: 2.28


g_main_context_get_thread_default ()

GMainContext *
g_main_context_get_thread_default (void);

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.

Returns

the thread-default GMainContext, or NULL if the thread-default context is the global default context.

[transfer none]

Since: 2.22


g_main_context_ref_thread_default ()

GMainContext *
g_main_context_ref_thread_default (void);

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.

Returns

the thread-default GMainContext. Unref with g_main_context_unref() when you are done with it.

[transfer full]

Since: 2.32


g_main_context_push_thread_default ()

void
g_main_context_push_thread_default (GMainContext *context);

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 may not need to ever call g_main_context_pop_thread_default(), assuming you want the new GMainContext to be the default for the whole lifecycle of the thread.

If you don't have control over how the new thread was created (e.g. in the new thread isn't newly created, or if the thread life cycle is managed by a GThreadPool), it is always suggested to wrap the logic that needs to use the new GMainContext inside a g_main_context_push_thread_default() / g_main_context_pop_thread_default() pair, otherwise threads that are re-used will end up never explicitly releasing the GMainContext reference they hold.

In some cases 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().

Parameters

context

a GMainContext, or NULL for the global default context.

[nullable]

Since: 2.22


g_main_context_pop_thread_default ()

void
g_main_context_pop_thread_default (GMainContext *context);

Pops context off the thread-default context stack (verifying that it was on the top of the stack).

Parameters

context

a GMainContext object, or NULL.

[nullable]

Since: 2.22


g_timeout_source_new ()

GSource *
g_timeout_source_new (guint interval);

Creates a new timeout source.

The source will not initially be associated with any GMainContext and must be added to one with g_source_attach() before it will be executed.

The interval given is in terms of monotonic time, not wall clock time. See g_get_monotonic_time().

Parameters

interval

the timeout interval in milliseconds.

 

Returns

the newly-created timeout source


g_timeout_source_new_seconds ()

GSource *
g_timeout_source_new_seconds (guint interval);

Creates a new timeout source.

The source will not initially be associated with any GMainContext and must be added to one with g_source_attach() before it will be executed.

The scheduling granularity/accuracy of this timeout source will be in seconds.

The interval given in terms of monotonic time, not wall clock time. See g_get_monotonic_time().

Parameters

interval

the timeout interval in seconds

 

Returns

the newly-created timeout source

Since: 2.14


g_timeout_add ()

guint
g_timeout_add (guint interval,
               GSourceFunc function,
               gpointer data);

Sets a function to be called at regular intervals, with the default priority, G_PRIORITY_DEFAULT. The function is called repeatedly until it returns FALSE, at which point the timeout is automatically destroyed and the function will not be called again. The first call to the function will be at the end of the first interval .

Note that timeout functions may be delayed, due to the processing of other event sources. Thus they should not be relied on for precise timing. After each call to the timeout function, the time of the next timeout is recalculated based on the current time and the given interval (it does not try to 'catch up' time lost in delays).

See memory management of sources for details on how to handle the return value and memory management of data .

If you want to have a timer in the "seconds" range and do not care about the exact time of the first call of the timer, use the g_timeout_add_seconds() function; this function allows for more optimizations and more efficient system power usage.

This internally creates a main loop source using g_timeout_source_new() and attaches it to the global GMainContext using g_source_attach(), so the callback will be invoked in whichever thread is running that main context. You can do these steps manually if you need greater control or to use a custom main context.

The interval given is in terms of monotonic time, not wall clock time. See g_get_monotonic_time().

Parameters

interval

the time between calls to the function, in milliseconds (1/1000ths of a second)

 

function

function to call

 

data

data to pass to function

 

Returns

the ID (greater than 0) of the event source.


g_timeout_add_full ()

guint
g_timeout_add_full (gint priority,
                    guint interval,
                    GSourceFunc function,
                    gpointer data,
                    GDestroyNotify notify);

Sets a function to be called at regular intervals, with the given priority. The function is called repeatedly until it returns FALSE, at which point the timeout is automatically destroyed and the function will not be called again. The notify function is called when the timeout is destroyed. The first call to the function will be at the end of the first interval .

Note that timeout functions may be delayed, due to the processing of other event sources. Thus they should not be relied on for precise timing. After each call to the timeout function, the time of the next timeout is recalculated based on the current time and the given interval (it does not try to 'catch up' time lost in delays).

See memory management of sources for details on how to handle the return value and memory management of data .

This internally creates a main loop source using g_timeout_source_new() and attaches it to the global GMainContext using g_source_attach(), so the callback will be invoked in whichever thread is running that main context. You can do these steps manually if you need greater control or to use a custom main context.

The interval given in terms of monotonic time, not wall clock time. See g_get_monotonic_time().

[rename-to g_timeout_add]

Parameters

priority

the priority of the timeout source. Typically this will be in the range between G_PRIORITY_DEFAULT and G_PRIORITY_HIGH.

 

interval

the time between calls to the function, in milliseconds (1/1000ths of a second)

 

function

function to call

 

data

data to pass to function

 

notify

function to call when the timeout is removed, or NULL.

[nullable]

Returns

the ID (greater than 0) of the event source.


g_timeout_add_seconds ()

guint
g_timeout_add_seconds (guint interval,
                       GSourceFunc function,
                       gpointer data);

Sets a function to be called at regular intervals with the default priority, G_PRIORITY_DEFAULT. The function is called repeatedly until it returns FALSE, at which point the timeout is automatically destroyed and the function will not be called again.

This internally creates a main loop source using g_timeout_source_new_seconds() and attaches it to the main loop context using g_source_attach(). You can do these steps manually if you need greater control. Also see g_timeout_add_seconds_full().

Note that the first call of the timer may not be precise for timeouts of one second. If you need finer precision and have such a timeout, you may want to use g_timeout_add() instead.

See memory management of sources for details on how to handle the return value and memory management of data .

The interval given is in terms of monotonic time, not wall clock time. See g_get_monotonic_time().

Parameters

interval

the time between calls to the function, in seconds

 

function

function to call

 

data

data to pass to function

 

Returns

the ID (greater than 0) of the event source.

Since: 2.14


g_timeout_add_seconds_full ()

guint
g_timeout_add_seconds_full (gint priority,
                            guint interval,
                            GSourceFunc function,
                            gpointer data,
                            GDestroyNotify notify);

Sets a function to be called at regular intervals, with priority . The function is called repeatedly until it returns FALSE, at which point the timeout is automatically destroyed and the function will not be called again.

Unlike g_timeout_add(), this function operates at whole second granularity. The initial starting point of the timer is determined by the implementation and the implementation is expected to group multiple timers together so that they fire all at the same time. To allow this grouping, the interval to the first timer is rounded and can deviate up to one second from the specified interval. Subsequent timer iterations will generally run at the specified interval.

Note that timeout functions may be delayed, due to the processing of other event sources. Thus they should not be relied on for precise timing. After each call to the timeout function, the time of the next timeout is recalculated based on the current time and the given interval

See memory management of sources for details on how to handle the return value and memory management of data .

If you want timing more precise than whole seconds, use g_timeout_add() instead.

The grouping of timers to fire at the same time results in a more power and CPU efficient behavior so if your timer is in multiples of seconds and you don't require the first timer exactly one second from now, the use of g_timeout_add_seconds() is preferred over g_timeout_add().

This internally creates a main loop source using g_timeout_source_new_seconds() and attaches it to the main loop context using g_source_attach(). You can do these steps manually if you need greater control.

The interval given is in terms of monotonic time, not wall clock time. See g_get_monotonic_time().

[rename-to g_timeout_add_seconds]

Parameters

priority

the priority of the timeout source. Typically this will be in the range between G_PRIORITY_DEFAULT and G_PRIORITY_HIGH.

 

interval

the time between calls to the function, in seconds

 

function

function to call

 

data

data to pass to function

 

notify

function to call when the timeout is removed, or NULL.

[nullable]

Returns

the ID (greater than 0) of the event source.

Since: 2.14


g_idle_source_new ()

GSource *
g_idle_source_new (void);

Creates a new idle source.

The source will not initially be associated with any GMainContext and must be added to one with g_source_attach() before it will be executed. Note that the default priority for idle sources is G_PRIORITY_DEFAULT_IDLE, as compared to other sources which have a default priority of G_PRIORITY_DEFAULT.

Returns

the newly-created idle source


g_idle_add ()

guint
g_idle_add (GSourceFunc function,
            gpointer data);

Adds a function to be called whenever there are no higher priority events pending to the default main loop. The function is given the default idle priority, G_PRIORITY_DEFAULT_IDLE. If the function returns FALSE it is automatically removed from the list of event sources and will not be called again.

See memory management of sources for details on how to handle the return value and memory management of data .

This internally creates a main loop source using g_idle_source_new() and attaches it to the global GMainContext using g_source_attach(), so the callback will be invoked in whichever thread is running that main context. You can do these steps manually if you need greater control or to use a custom main context.

Parameters

function

function to call

 

data

data to pass to function .

 

Returns

the ID (greater than 0) of the event source.


g_idle_add_full ()

guint
g_idle_add_full (gint priority,
                 GSourceFunc function,
                 gpointer data,
                 GDestroyNotify notify);

Adds a function to be called whenever there are no higher priority events pending. If the function returns FALSE it is automatically removed from the list of event sources and will not be called again.

See memory management of sources for details on how to handle the return value and memory management of data .

This internally creates a main loop source using g_idle_source_new() and attaches it to the global GMainContext using g_source_attach(), so the callback will be invoked in whichever thread is running that main context. You can do these steps manually if you need greater control or to use a custom main context.

[rename-to g_idle_add]

Parameters

priority

the priority of the idle source. Typically this will be in the range between G_PRIORITY_DEFAULT_IDLE and G_PRIORITY_HIGH_IDLE.

 

function

function to call

 

data

data to pass to function

 

notify

function to call when the idle is removed, or NULL.

[nullable]

Returns

the ID (greater than 0) of the event source.


g_idle_remove_by_data ()

gboolean
g_idle_remove_by_data (gpointer data);

Removes the idle function with the given data.

Parameters

data

the data for the idle source's callback.

 

Returns

TRUE if an idle source was found and removed.


GChildWatchFunc ()

void
(*GChildWatchFunc) (GPid pid,
                    gint status,
                    gpointer user_data);

Prototype of a GChildWatchSource callback, called when a child process has exited. To interpret status , see the documentation for g_spawn_check_exit_status().

Parameters

pid

the process id of the child process

 

status

Status information about the child process, encoded in a platform-specific manner

 

user_data

user data passed to g_child_watch_add()

 

g_child_watch_source_new ()

GSource *
g_child_watch_source_new (GPid pid);

Creates a new child_watch source.

The source will not initially be associated with any GMainContext and must be added to one with g_source_attach() before it will be executed.

Note that child watch sources can only be used in conjunction with g_spawn... when the G_SPAWN_DO_NOT_REAP_CHILD flag is used.

Note that on platforms where GPid must be explicitly closed (see g_spawn_close_pid()) pid must not be closed while the source is still active. Typically, you will want to call g_spawn_close_pid() in the callback function for the source.

Note further that using g_child_watch_source_new() is not compatible with calling waitpid with a nonpositive first argument in the application. Calling waitpid() for individual pids will still work fine.

Similarly, on POSIX platforms, the pid passed to this function must be greater than 0 (i.e. this function must wait for a specific child, and cannot wait for one of many children by using a nonpositive argument).

Parameters

pid

process to watch. On POSIX the positive pid of a child process. On Windows a handle for a process (which doesn't have to be a child).

 

Returns

the newly-created child watch source

Since: 2.4


g_child_watch_add ()

guint
g_child_watch_add (GPid pid,
                   GChildWatchFunc function,
                   gpointer data);

Sets a function to be called when the child indicated by pid exits, at a default priority, G_PRIORITY_DEFAULT.

If you obtain pid from g_spawn_async() or g_spawn_async_with_pipes() you will need to pass G_SPAWN_DO_NOT_REAP_CHILD as flag to the spawn function for the child watching to work.

Note that on platforms where GPid must be explicitly closed (see g_spawn_close_pid()) pid must not be closed while the source is still active. Typically, you will want to call g_spawn_close_pid() in the callback function for the source.

GLib supports only a single callback per process id.

This internally creates a main loop source using g_child_watch_source_new() and attaches it to the main loop context using g_source_attach(). You can do these steps manually if you need greater control.

Parameters

pid

process id to watch. On POSIX the positive pid of a child process. On Windows a handle for a process (which doesn't have to be a child).

 

function

function to call

 

data

data to pass to function

 

Returns

the ID (greater than 0) of the event source.

Since: 2.4


g_child_watch_add_full ()

guint
g_child_watch_add_full (gint priority,
                        GPid pid,
                        GChildWatchFunc function,
                        gpointer data,
                        GDestroyNotify notify);

Sets a function to be called when the child indicated by pid exits, at the priority priority .

If you obtain pid from g_spawn_async() or g_spawn_async_with_pipes() you will need to pass G_SPAWN_DO_NOT_REAP_CHILD as flag to the spawn function for the child watching to work.

In many programs, you will want to call g_spawn_check_exit_status() in the callback to determine whether or not the child exited successfully.

Also, note that on platforms where GPid must be explicitly closed (see g_spawn_close_pid()) pid must not be closed while the source is still active. Typically, you should invoke g_spawn_close_pid() in the callback function for the source.

GLib supports only a single callback per process id.

This internally creates a main loop source using g_child_watch_source_new() and attaches it to the main loop context using g_source_attach(). You can do these steps manually if you need greater control.

[rename-to g_child_watch_add]

Parameters

priority

the priority of the idle source. Typically this will be in the range between G_PRIORITY_DEFAULT_IDLE and G_PRIORITY_HIGH_IDLE.

 

pid

process to watch. On POSIX the positive pid of a child process. On Windows a handle for a process (which doesn't have to be a child).

 

function

function to call

 

data

data to pass to function

 

notify

function to call when the idle is removed, or NULL.

[nullable]

Returns

the ID (greater than 0) of the event source.

Since: 2.4


g_poll ()

gint
g_poll (GPollFD *fds,
        guint nfds,
        gint timeout);

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().

Parameters

fds

file descriptors to poll

 

nfds

the number of file descriptors in fds

 

timeout

amount of time to wait, in milliseconds, or -1 to wait forever

 

Returns

the number of entries in fds whose revents fields were filled in, or 0 if the operation timed out, or -1 on error or if the call was interrupted.

Since: 2.20


GSourceDummyMarshal ()

void
(*GSourceDummyMarshal) (void);

This is just a placeholder for GClosureMarshal, which cannot be used here for dependency reasons.


g_source_new ()

GSource *
g_source_new (GSourceFuncs *source_funcs,
              guint struct_size);

Creates a new GSource structure. The size is specified to allow creating structures derived from GSource that contain additional data. The size passed in must be at least sizeof (GSource).

The source will not initially be associated with any GMainContext and must be added to one with g_source_attach() before it will be executed.

Parameters

source_funcs

structure containing functions that implement the sources behavior.

 

struct_size

size of the GSource structure to create.

 

Returns

the newly-created GSource.


g_source_ref ()

GSource *
g_source_ref (GSource *source);

Increases the reference count on a source by one.

Parameters

source

a GSource

 

Returns

source


g_source_unref ()

void
g_source_unref (GSource *source);

Decreases the reference count of a source by one. If the resulting reference count is zero the source and associated memory will be destroyed.

Parameters

source

a GSource

 

g_source_set_funcs ()

void
g_source_set_funcs (GSource *source,
                    GSourceFuncs *funcs);

Sets the source functions (can be used to override default implementations) of an unattached source.

Parameters

source

a GSource

 

funcs

the new GSourceFuncs

 

Since: 2.12


g_source_attach ()

guint
g_source_attach (GSource *source,
                 GMainContext *context);

Adds a GSource to a context so that it will be executed within that context. Remove it by calling g_source_destroy().

Parameters

source

a GSource

 

context

a GMainContext (if NULL, the default context will be used).

[nullable]

Returns

the ID (greater than 0) for the source within the GMainContext.


g_source_destroy ()

void
g_source_destroy (GSource *source);

Removes a source from its GMainContext, if any, and mark it as destroyed. The source cannot be subsequently added to another context. It is safe to call this on sources which have already been removed from their context.

Parameters

source

a GSource

 

g_source_is_destroyed ()

gboolean
g_source_is_destroyed (GSource *source);

Returns whether source has been destroyed.

This is important when you operate upon your objects from within idle handlers, but may have freed the object before the dispatch of your idle handler.

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static gboolean 
idle_callback (gpointer data)
{
  SomeWidget *self = data;
   
  GDK_THREADS_ENTER ();
  // do stuff with self
  self->idle_id = 0;
  GDK_THREADS_LEAVE ();
   
  return G_SOURCE_REMOVE;
}
 
static void 
some_widget_do_stuff_later (SomeWidget *self)
{
  self->idle_id = g_idle_add (idle_callback, self);
}
 
static void 
some_widget_finalize (GObject *object)
{
  SomeWidget *self = SOME_WIDGET (object);
   
  if (self->idle_id)
    g_source_remove (self->idle_id);
   
  G_OBJECT_CLASS (parent_class)->finalize (object);
}

This will fail in a multi-threaded application if the widget is destroyed before the idle handler fires due to the use after free in the callback. A solution, to this particular problem, is to check to if the source has already been destroy within the callback.

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static gboolean 
idle_callback (gpointer data)
{
  SomeWidget *self = data;
  
  GDK_THREADS_ENTER ();
  if (!g_source_is_destroyed (g_main_current_source ()))
    {
      // do stuff with self
    }
  GDK_THREADS_LEAVE ();
  
  return FALSE;
}

Calls to this function from a thread other than the one acquired by the GMainContext the GSource is attached to are typically redundant, as the source could be destroyed immediately after this function returns. However, once a source is destroyed it cannot be un-destroyed, so this function can be used for opportunistic checks from any thread.

Parameters

source

a GSource

 

Returns

TRUE if the source has been destroyed

Since: 2.12


g_source_set_priority ()

void
g_source_set_priority (GSource *source,
                       gint priority);

Sets the priority of a source. While the main loop is being run, a source will be dispatched if it is ready to be dispatched and no sources at a higher (numerically smaller) priority are ready to be dispatched.

A child source always has the same priority as its parent. It is not permitted to change the priority of a source once it has been added as a child of another source.

Parameters

source

a GSource

 

priority

the new priority.

 

g_source_get_priority ()

gint
g_source_get_priority (GSource *source);

Gets the priority of a source.

Parameters

source

a GSource

 

Returns

the priority of the source


g_source_set_can_recurse ()

void
g_source_set_can_recurse (GSource *source,
                          gboolean can_recurse);

Sets whether a source can be called recursively. If can_recurse is TRUE, then while the source is being dispatched then this source will be processed normally. Otherwise, all processing of this source is blocked until the dispatch function returns.

Parameters

source

a GSource

 

can_recurse

whether recursion is allowed for this source

 

g_source_get_can_recurse ()

gboolean
g_source_get_can_recurse (GSource *source);

Checks whether a source is allowed to be called recursively. see g_source_set_can_recurse().

Parameters

source

a GSource

 

Returns

whether recursion is allowed.


g_source_get_id ()

guint
g_source_get_id (GSource *source);

Returns the numeric ID for a particular source. The ID of a source is a positive integer which is unique within a particular main loop context. The reverse mapping from ID to source is done by g_main_context_find_source_by_id().

Parameters

source

a GSource

 

Returns

the ID (greater than 0) for the source


g_source_get_name ()

const char *
g_source_get_name (GSource *source);

Gets a name for the source, used in debugging and profiling. The name may be NULL if it has never been set with g_source_set_name().

Parameters

source

a GSource

 

Returns

the name of the source

Since: 2.26


g_source_set_name ()

void
g_source_set_name (GSource *source,
                   const char *name);

Sets a name for the source, used in debugging and profiling. The name defaults to NULL.

The source name should describe in a human-readable way what the source does. For example, "X11 event queue" or "GTK+ repaint idle handler" or whatever it is.

It is permitted to call this function multiple times, but is not recommended due to the potential performance impact. For example, one could change the name in the "check" function of a GSourceFuncs to include details like the event type in the source name.

Use caution if changing the name while another thread may be accessing it with g_source_get_name(); that function does not copy the value, and changing the value will free it while the other thread may be attempting to use it.

Parameters

source

a GSource

 

name

debug name for the source

 

Since: 2.26


g_source_set_name_by_id ()

void
g_source_set_name_by_id (guint tag,
                         const char *name);

Sets the name of a source using its ID.

This is a convenience utility to set source names from the return value of g_idle_add(), g_timeout_add(), etc.

It is a programmer error to attempt to set the name of a non-existent source.

More specifically: source IDs can be reissued after a source has been destroyed and therefore it is never valid to use this function with a source ID which may have already been removed. An example is when scheduling an idle to run in another thread with g_idle_add(): the idle may already have run and been removed by the time this function is called on its (now invalid) source ID. This source ID may have been reissued, leading to the operation being performed against the wrong source.

Parameters

tag

a GSource ID

 

name

debug name for the source

 

Since: 2.26


g_source_get_context ()

GMainContext *
g_source_get_context (GSource *source);

Gets the GMainContext with which the source is associated.

You can call this on a source that has been destroyed, provided that the GMainContext it was attached to still exists (in which case it will return that GMainContext). In particular, you can always call this function on the source returned from g_main_current_source(). But calling this function on a source whose GMainContext has been destroyed is an error.

Parameters

source

a GSource

 

Returns

the GMainContext with which the source is associated, or NULL if the context has not yet been added to a source.

[transfer none][nullable]


g_source_set_callback ()

void
g_source_set_callback (GSource *source,
                       GSourceFunc func,
                       gpointer data,
                       GDestroyNotify notify);

Sets the callback function for a source. The callback for a source is called from the source's dispatch function.

The exact type of func depends on the type of source; ie. you should not count on func being called with data as its first parameter.

See memory management of sources for details on how to handle memory management of data .

Typically, you won't use this function. Instead use functions specific to the type of source you are using.

Parameters

source

the source

 

func

a callback function

 

data

the data to pass to callback function

 

notify

a function to call when data is no longer in use, or NULL.

[nullable]

GSourceFunc ()

gboolean
(*GSourceFunc) (gpointer user_data);

Specifies the type of function passed to g_timeout_add(), g_timeout_add_full(), g_idle_add(), and g_idle_add_full().

Parameters

user_data

data passed to the function, set when the source was created with one of the above functions

 

Returns

FALSE if the source should be removed. G_SOURCE_CONTINUE and G_SOURCE_REMOVE are more memorable names for the return value.


g_source_set_callback_indirect ()

void
g_source_set_callback_indirect (GSource *source,
                                gpointer callback_data,
                                GSourceCallbackFuncs *callback_funcs);

Sets the callback function storing the data as a refcounted callback "object". This is used internally. Note that calling g_source_set_callback_indirect() assumes an initial reference count on callback_data , and thus callback_funcs->unref will eventually be called once more than callback_funcs->ref .

Parameters

source

the source

 

callback_data

pointer to callback data "object"

 

callback_funcs

functions for reference counting callback_data and getting the callback and data

 

g_source_set_ready_time ()

void
g_source_set_ready_time (GSource *source,
                         gint64 ready_time);

Sets a GSource to be dispatched when the given monotonic time is reached (or passed). If the monotonic time is in the past (as it always will be if ready_time is 0) then the source will be dispatched immediately.

If ready_time is -1 then the source is never woken up on the basis of the passage of time.

Dispatching the source does not reset the ready time. You should do so yourself, from the source dispatch function.

Note that if you have a pair of sources where the ready time of one suggests that it will be delivered first but the priority for the other suggests that it would be delivered first, and the ready time for both sources is reached during the same main context iteration then the order of dispatch is undefined.

It is a no-op to call this function on a GSource which has already been destroyed with g_source_destroy().

This API is only intended to be used by implementations of GSource. Do not call this API on a GSource that you did not create.

Parameters

source

a GSource

 

ready_time

the monotonic time at which the source will be ready, 0 for "immediately", -1 for "never"

 

Since: 2.36


g_source_get_ready_time ()

gint64
g_source_get_ready_time (GSource *source);

Gets the "ready time" of source , as set by g_source_set_ready_time().

Any time before the current monotonic time (including 0) is an indication that the source will fire immediately.

Parameters

source

a GSource

 

Returns

the monotonic ready time, -1 for "never"


g_source_add_unix_fd ()

gpointer
g_source_add_unix_fd (GSource *source,
                      gint fd,
                      GIOCondition events);

Monitors fd for the IO events in events .

The tag returned by this function can be used to remove or modify the monitoring of the fd using g_source_remove_unix_fd() or g_source_modify_unix_fd().

It is not necessary to remove the fd before destroying the source; it will be cleaned up automatically.

This API is only intended to be used by implementations of GSource. Do not call this API on a GSource that you did not create.

As the name suggests, this function is not available on Windows.

Parameters

source

a GSource

 

fd

the fd to monitor

 

events

an event mask

 

Returns

an opaque tag.

[not nullable]

Since: 2.36


g_source_remove_unix_fd ()

void
g_source_remove_unix_fd (GSource *source,
                         gpointer tag);

Reverses the effect of a previous call to g_source_add_unix_fd().

You only need to call this if you want to remove an fd from being watched while keeping the same source around. In the normal case you will just want to destroy the source.

This API is only intended to be used by implementations of GSource. Do not call this API on a GSource that you did not create.

As the name suggests, this function is not available on Windows.

Parameters

source

a GSource

 

tag

the tag from g_source_add_unix_fd().

[not nullable]

Since: 2.36


g_source_modify_unix_fd ()

void
g_source_modify_unix_fd (GSource *source,
                         gpointer tag,
                         GIOCondition new_events);

Updates the event mask to watch for the fd identified by tag .

tag is the tag returned from g_source_add_unix_fd().

If you want to remove a fd, don't set its event mask to zero. Instead, call g_source_remove_unix_fd().

This API is only intended to be used by implementations of GSource. Do not call this API on a GSource that you did not create.

As the name suggests, this function is not available on Windows.

Parameters

source

a GSource

 

tag

the tag from g_source_add_unix_fd().

[not nullable]

new_events

the new event mask to watch

 

Since: 2.36


g_source_query_unix_fd ()

GIOCondition
g_source_query_unix_fd (GSource *source,
                        gpointer tag);

Queries the events reported for the fd corresponding to tag on source during the last poll.

The return value of this function is only defined when the function is called from the check or dispatch functions for source .

This API is only intended to be used by implementations of GSource. Do not call this API on a GSource that you did not create.

As the name suggests, this function is not available on Windows.

Parameters

source

a GSource

 

tag

the tag from g_source_add_unix_fd().

[not nullable]

Returns

the conditions reported on the fd

Since: 2.36


g_source_add_poll ()

void
g_source_add_poll (GSource *source,
                   GPollFD *fd);

Adds a file descriptor to the set of file descriptors polled for this source. This is usually combined with g_source_new() to add an event source. The event source's check function will typically test the revents field in the GPollFD struct and return TRUE if events need to be processed.

This API is only intended to be used by implementations of GSource. Do not call this API on a GSource that you did not create.

Using this API forces the linear scanning of event sources on each main loop iteration. Newly-written event sources should try to use g_source_add_unix_fd() instead of this API.

Parameters

source

a GSource

 

fd

a GPollFD structure holding information about a file descriptor to watch.

 

g_source_remove_poll ()

void
g_source_remove_poll (GSource *source,
                      GPollFD *fd);

Removes a file descriptor from the set of file descriptors polled for this source.

This API is only intended to be used by implementations of GSource. Do not call this API on a GSource that you did not create.

Parameters

source

a GSource

 

fd

a GPollFD structure previously passed to g_source_add_poll().

 

g_source_add_child_source ()

void
g_source_add_child_source (GSource *source,
                           GSource *child_source);

Adds child_source to source as a "polled" source; when source is added to a GMainContext, child_source will be automatically added with the same priority, when child_source is triggered, it will cause source to dispatch (in addition to calling its own callback), and when source is destroyed, it will destroy child_source as well. (source will also still be dispatched if its own prepare/check functions indicate that it is ready.)

If you don't need child_source to do anything on its own when it triggers, you can call g_source_set_dummy_callback() on it to set a callback that does nothing (except return TRUE if appropriate).

source will hold a reference on child_source while child_source is attached to it.

This API is only intended to be used by implementations of GSource. Do not call this API on a GSource that you did not create.

Parameters

source

a GSource

 

child_source

a second GSource that source should "poll"

 

Since: 2.28


g_source_remove_child_source ()

void
g_source_remove_child_source (GSource *source,
                              GSource *child_source);

Detaches child_source from source and destroys it.

This API is only intended to be used by implementations of GSource. Do not call this API on a GSource that you did not create.

Parameters

source

a GSource

 

child_source

a GSource previously passed to g_source_add_child_source().

 

Since: 2.28


g_source_get_time ()

gint64
g_source_get_time (GSource *source);

Gets the time to be used when checking this source. The advantage of calling this function over calling g_get_monotonic_time() directly is that when checking multiple sources, GLib can cache a single value instead of having to repeatedly get the system monotonic time.

The time here is the system monotonic time, if available, or some other reasonable alternative otherwise. See g_get_monotonic_time().

Parameters

source

a GSource

 

Returns

the monotonic time in microseconds

Since: 2.28


g_source_get_current_time ()

void
g_source_get_current_time (GSource *source,
                           GTimeVal *timeval);

g_source_get_current_time has been deprecated since version 2.28 and should not be used in newly-written code.

use g_source_get_time() instead

This function ignores source and is otherwise the same as g_get_current_time().

Parameters

source

a GSource

 

timeval

GTimeVal structure in which to store current time.

 

g_source_remove ()

gboolean
g_source_remove (guint tag);

Removes the source with the given id from the default main context.

The id of a GSource is given by g_source_get_id(), or will be returned by the functions g_source_attach(), g_idle_add(), g_idle_add_full(), g_timeout_add(), g_timeout_add_full(), g_child_watch_add(), g_child_watch_add_full(), g_io_add_watch(), and g_io_add_watch_full().

See also g_source_destroy(). You must use g_source_destroy() for sources added to a non-default main context.

It is a programmer error to attempt to remove a non-existent source.

More specifically: source IDs can be reissued after a source has been destroyed and therefore it is never valid to use this function with a source ID which may have already been removed. An example is when scheduling an idle to run in another thread with g_idle_add(): the idle may already have run and been removed by the time this function is called on its (now invalid) source ID. This source ID may have been reissued, leading to the operation being performed against the wrong source.

Parameters

tag

the ID of the source to remove.

 

Returns

For historical reasons, this function always returns TRUE


g_source_remove_by_funcs_user_data ()

gboolean
g_source_remove_by_funcs_user_data (GSourceFuncs *funcs,
                                    gpointer user_data);

Removes a source from the default main loop context given the source functions and user data. If multiple sources exist with the same source functions and user data, only one will be destroyed.

Parameters

funcs

The source_funcs passed to g_source_new()

 

user_data

the user data for the callback

 

Returns

TRUE if a source was found and removed.


g_source_remove_by_user_data ()

gboolean
g_source_remove_by_user_data (gpointer user_data);

Removes a source from the default main loop context given the user data for the callback. If multiple sources exist with the same user data, only one will be destroyed.

Parameters

user_data

the user_data for the callback.

 

Returns

TRUE if a source was found and removed.

Types and Values

GMainLoop

typedef struct _GMainLoop GMainLoop;

The GMainLoop struct is an opaque data type representing the main event loop of a GLib or GTK+ application.


G_PRIORITY_HIGH

#define G_PRIORITY_HIGH            -100

Use this for high priority event sources.

It is not used within GLib or GTK+.


G_PRIORITY_DEFAULT

#define G_PRIORITY_DEFAULT          0

Use this for default priority event sources.

In GLib this priority is used when adding timeout functions with g_timeout_add(). In GDK this priority is used for events from the X server.


G_PRIORITY_HIGH_IDLE

#define G_PRIORITY_HIGH_IDLE        100

Use this for high priority idle functions.

GTK+ uses G_PRIORITY_HIGH_IDLE + 10 for resizing operations, and G_PRIORITY_HIGH_IDLE + 20 for redrawing operations. (This is done to ensure that any pending resizes are processed before any pending redraws, so that widgets are not redrawn twice unnecessarily.)


G_PRIORITY_DEFAULT_IDLE

#define G_PRIORITY_DEFAULT_IDLE     200

Use this for default priority idle functions.

In GLib this priority is used when adding idle functions with g_idle_add().


G_PRIORITY_LOW

#define G_PRIORITY_LOW              300

Use this for very low priority background tasks.

It is not used within GLib or GTK+.


G_SOURCE_CONTINUE

#define G_SOURCE_CONTINUE       TRUE

Use this macro as the return value of a GSourceFunc to leave the GSource in the main loop.

Since: 2.32


G_SOURCE_REMOVE

#define G_SOURCE_REMOVE         FALSE

Use this macro as the return value of a GSourceFunc to remove the GSource from the main loop.

Since: 2.32


GMainContext

typedef struct _GMainContext GMainContext;

The GMainContext struct is an opaque data type representing a set of sources to be handled in a main loop.


GPid

typedef int GPid;

A type which is used to hold a process identification.

On UNIX, processes are identified by a process id (an integer), while Windows uses process handles (which are pointers).

GPid is used in GLib only for descendant processes spawned with the g_spawn functions.


G_PID_FORMAT

#define G_PID_FORMAT "i"

A format specifier that can be used in printf()-style format strings when printing a GPid.

Since: 2.50


struct GPollFD

struct GPollFD {
#if defined (G_OS_WIN32) && GLIB_SIZEOF_VOID_P == 8
#endif
#else
  gint		fd;
#endif
  gushort 	events;
  gushort 	revents;
};

Represents a file descriptor, which events to poll for, and which events occurred.

Members

gint fd;

the file descriptor to poll (or a HANDLE on Win32)

 

gushort events;

a bitwise combination from GIOCondition, specifying which events should be polled for. Typically for reading from a file descriptor you would use G_IO_IN | G_IO_HUP | G_IO_ERR, and for writing you would use G_IO_OUT | G_IO_ERR.

 

gushort revents;

a bitwise combination of flags from GIOCondition, returned from the poll() function to indicate which events occurred.

 

G_POLLFD_FORMAT

#define G_POLLFD_FORMAT "%d"

A format specifier that can be used in printf()-style format strings when printing the fd member of a GPollFD.


struct GSource

struct GSource {
};

The GSource struct is an opaque data type representing an event source.


struct GSourceFuncs

struct GSourceFuncs {
  gboolean (*prepare)  (GSource    *source,
                        gint       *timeout_);
  gboolean (*check)    (GSource    *source);
  gboolean (*dispatch) (GSource    *source,
                        GSourceFunc callback,
                        gpointer    user_data);
  void     (*finalize) (GSource    *source); /* Can be NULL */
};

The GSourceFuncs struct contains a table of functions used to handle event sources in a generic manner.

For idle sources, the prepare and check functions always return TRUE to indicate that the source is always ready to be processed. The prepare function also returns a timeout value of 0 to ensure that the poll() call doesn't block (since that would be time wasted which could have been spent running the idle function).

For timeout sources, the prepare and check functions both return TRUE if the timeout interval has expired. The prepare function also returns a timeout value to ensure that the poll() call doesn't block too long and miss the next timeout.

For file descriptor sources, the prepare function typically returns FALSE, since it must wait until poll() has been called before it knows whether any events need to be processed. It sets the returned timeout to -1 to indicate that it doesn't mind how long the poll() call blocks. In the check function, it tests the results of the poll() call to see if the required condition has been met, and returns TRUE if so.

Members

prepare ()

Called before all the file descriptors are polled. If the source can determine that it is ready here (without waiting for the results of the poll() call) it should return TRUE. It can also return a timeout_ value which should be the maximum timeout (in milliseconds) which should be passed to the poll() call. The actual timeout used will be -1 if all sources returned -1, or it will be the minimum of all the timeout_ values returned which were >= 0. Since 2.36 this may be NULL, in which case the effect is as if the function always returns FALSE with a timeout of -1. If prepare returns a timeout and the source also has a 'ready time' set then the nearer of the two will be used.

 

check ()

Called after all the file descriptors are polled. The source should return TRUE if it is ready to be dispatched. Note that some time may have passed since the previous prepare function was called, so the source should be checked again here. Since 2.36 this may be NULL, in which case the effect is as if the function always returns FALSE.

 

dispatch ()

Called to dispatch the event source, after it has returned TRUE in either its prepare or its check function. The dispatch function is passed in a callback function and data. The callback function may be NULL if the source was never connected to a callback using g_source_set_callback(). The dispatch function should call the callback function with user_data and whatever additional parameters are needed for this type of event source. The return value of the dispatch function should be G_SOURCE_REMOVE if the source should be removed or G_SOURCE_CONTINUE to keep it.

 

finalize ()

Called when the source is finalized.

 

struct GSourceCallbackFuncs

struct GSourceCallbackFuncs {
  void (*ref)   (gpointer     cb_data);
  void (*unref) (gpointer     cb_data);
  void (*get)   (gpointer     cb_data,
                 GSource     *source, 
                 GSourceFunc *func,
                 gpointer    *data);
};

The GSourceCallbackFuncs struct contains functions for managing callback objects.

Members

ref ()

Called when a reference is added to the callback object

 

unref ()

Called when a reference to the callback object is dropped

 

get ()

Called to extract the callback function and data from the callback object.