Source#

class Source(*args, **kwargs)#

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

Constructors#

class Source
classmethod new(source_funcs: SourceFuncs, struct_size: int) → Source#

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

The source will not initially be associated with any MainContext and must be added to one with attach before it will be executed.

Parameters:

  • source_funcs – structure containing functions that implement the sources behavior.

  • struct_size – size of the Source structure to create.

Methods#

class Source
add_child_source(child_source: Source) → None#

Adds child_source to source as a “polled” source; when source is added to a MainContext, 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 Source. Do not call this API on a Source that you did not create.

Added in version 2.28.

Parameters:

child_source – a second Source that source should “poll”

add_poll(fd: PollFD) → None#

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

This API is only intended to be used by implementations of Source. Do not call this API on a Source 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:

fd – a PollFD structure holding information about a file descriptor to watch.

add_unix_fd(fd: int, events: IOCondition) → Any#

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 remove_unix_fd or 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 Source. Do not call this API on a Source that you did not create.

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

Added in version 2.36.

Parameters:

  • fd – the fd to monitor

  • events – an event mask

attach(context: MainContext | None = None) → int#

Adds a Source to a context so that it will be executed within that context. Remove it by calling destroy.

This function is safe to call from any thread, regardless of which thread the context is running in.

Parameters:

context – a MainContext (if None, the global-default main context will be used)

destroy() → None#

Removes a source from its MainContext, 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.

This does not unref the Source: if you still hold a reference, use unref to drop it.

This function is safe to call from any thread, regardless of which thread the MainContext is running in.

If the source is currently attached to a MainContext, destroying it will effectively unset the callback similar to calling set_callback. This can mean, that the data’s DestroyNotify gets called right away.

finalize()#
get_can_recurse() → bool#

Checks whether a source is allowed to be called recursively. see set_can_recurse.

get_context() → MainContext | None#

Gets the MainContext with which the source is associated.

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

get_current_time()#

This function ignores source and is otherwise the same as get_current_time.

Deprecated since version 2.28: use get_time instead

get_id() → int#

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 find_source_by_id.

You can only call this function while the source is associated to a MainContext instance; calling this function before attach or after destroy yields undefined behavior. The ID returned is unique within the MainContext instance passed to attach.

get_name() → str | None#

Gets a name for the source, used in debugging and profiling. The name may be None if it has never been set with set_name.

Added in version 2.26.

get_priority() → int#

Gets the priority of a source.

get_ready_time() → int#

Gets the “ready time” of source, as set by set_ready_time.

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

get_time() → int#

Gets the time to be used when checking this source. The advantage of calling this function over calling 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 get_monotonic_time.

Added in version 2.28.

is_destroyed() → bool#

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.

static gboolean
idle_callback (gpointer data)
{
  SomeWidget *self = data;

  g_mutex_lock (&self->idle_id_mutex);
  // do stuff with self
  self->idle_id = 0;
  g_mutex_unlock (&self->idle_id_mutex);

  return G_SOURCE_REMOVE;
}

static void
some_widget_do_stuff_later (SomeWidget *self)
{
  g_mutex_lock (&self->idle_id_mutex);
  self->idle_id = g_idle_add (idle_callback, self);
  g_mutex_unlock (&self->idle_id_mutex);
}

static void
some_widget_init (SomeWidget *self)
{
  g_mutex_init (&self->idle_id_mutex);

  // ...
}

static void
some_widget_finalize (GObject *object)
{
  SomeWidget *self = SOME_WIDGET (object);

  if (self->idle_id)
    g_source_remove (self->idle_id);

  g_mutex_clear (&self->idle_id_mutex);

  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.

static gboolean
idle_callback (gpointer data)
{
  SomeWidget *self = data;

  g_mutex_lock (&self->idle_id_mutex);
  if (!g_source_is_destroyed (g_main_current_source ()))
    {
      // do stuff with self
    }
  g_mutex_unlock (&self->idle_id_mutex);

  return FALSE;
}

Calls to this function from a thread other than the one acquired by the MainContext the Source 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.

Added in version 2.12.

modify_unix_fd(tag: Any, new_events: IOCondition) → None#

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

tag is the tag returned from add_unix_fd.

If you want to remove a fd, don’t set its event mask to zero. Instead, call remove_unix_fd.

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

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

Added in version 2.36.

Parameters:

  • tag – the tag from add_unix_fd

  • new_events – the new event mask to watch

query_unix_fd(tag: Any) → IOCondition#

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 Source. Do not call this API on a Source that you did not create.

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

Added in version 2.36.

Parameters:

tag – the tag from add_unix_fd

classmethod remove() → bool#

Removes the source with the given ID from the default main context. You must use destroy for sources added to a non-default main context.

The ID of a Source is given by get_id, or will be returned by the functions attach, idle_add, idle_add_full, timeout_add, timeout_add_full, child_watch_add, child_watch_add_full, io_add_watch, and io_add_watch_full.

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 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.

Returns:

0 if the file was successfully removed, -1 if an error occurred

classmethod remove_by_funcs_user_data(user_data: Any = None) → bool#

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:

user_data – the user data for the callback

classmethod remove_by_user_data() → bool#

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.

remove_child_source(child_source: Source) → None#

Detaches child_source from source and destroys it.

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

Added in version 2.28.

Parameters:

child_source – a Source previously passed to add_child_source.

remove_poll(fd: PollFD) → None#

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 Source. Do not call this API on a Source that you did not create.

Parameters:

fd – a PollFD structure previously passed to add_poll.

remove_unix_fd(tag: Any) → None#

Reverses the effect of a previous call to 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 Source. Do not call this API on a Source that you did not create.

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

Added in version 2.36.

Parameters:

tag – the tag from add_unix_fd

set_callback(fn, user_data=None)#

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. Cast func with SOURCE_FUNC to avoid warnings about incompatible function types.

See mainloop memory management 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, such as idle_add or timeout_add.

It is safe to call this function multiple times on a source which has already been attached to a context. The changes will take effect for the next time the source is dispatched after this call returns.

Note that destroy for a currently attached source has the effect of also unsetting the callback.

Parameters:

  • fn

  • user_data

set_callback_indirect(callback_data: Any, callback_funcs: SourceCallbackFuncs) → None#

Sets the callback function storing the data as a refcounted callback “object”. This is used internally. Note that calling 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.

It is safe to call this function multiple times on a source which has already been attached to a context. The changes will take effect for the next time the source is dispatched after this call returns.

Parameters:

  • callback_data – pointer to callback data “object”

  • callback_funcs – functions for reference counting callback_data and getting the callback and data

set_can_recurse(can_recurse: bool) → None#

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:

can_recurse – whether recursion is allowed for this source

set_funcs(funcs: SourceFuncs) → None#

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

Added in version 2.12.

Parameters:

funcs – the new SourceFuncs

set_name(name: str) → None#

Sets a name for the source, used in debugging and profiling. The name defaults to None.

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 SourceFuncs 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 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.

Also see set_static_name.

Added in version 2.26.

Parameters:

name – debug name for the source

classmethod set_name_by_id(name: str) → None#

Sets the name of a source using its ID.

This is a convenience utility to set source names from the return value of idle_add, 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 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.

Added in version 2.26.

Parameters:

name – debug name for the source

set_priority(priority: int) → None#

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:

priority – the new priority.

set_ready_time(ready_time: int) → None#

Sets a Source 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 Source which has already been destroyed with destroy.

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

Added in version 2.36.

Parameters:

ready_time – the monotonic time at which the source will be ready, 0 for “immediately”, -1 for “never”

set_static_name(name: str) → None#

A variant of set_name that does not duplicate the name, and can only be used with string literals.

Added in version 2.70.

Parameters:

name – debug name for the source

Fields#

class Source
callback_data#
callback_funcs#
can_recurse#
context#
flags#
name#
next#
poll_fds#
prev#
priority#
priv#
ref_count#
source_funcs#
source_id#