Struct glib::Source

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#[repr(transparent)]
pub struct Source { /* private fields */ }

Expand description

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

Implementations

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impl Source

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pub fn add_child_source(&self, child_source: &Source)

Adds child_source to self as a “polled” source; when self is added to a MainContext, child_source will be automatically added with the same priority, when child_source is triggered, it will cause self to dispatch (in addition to calling its own callback), and when self is destroyed, it will destroy child_source as well. (self 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).

self 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.

`child_source`

a second Source that self should “poll”

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pub fn destroy(&self)

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pub fn can_recurse(&self) -> bool

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

Returns

whether recursion is allowed.

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pub fn context(&self) -> Option<MainContext>

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.

Returns

the MainContext with which the source is associated, or None if the context has not yet been added to a source.

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pub fn name(&self) -> Option<GString>

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

Returns

the name of the source

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pub fn priority(&self) -> i32

Gets the priority of a source.

Returns

the priority of the source

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pub fn ready_time(&self) -> i64

Gets the “ready time” of self, 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.

Returns

the monotonic ready time, -1 for “never”

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pub fn time(&self) -> i64

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

Returns

the monotonic time in microseconds

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pub fn is_destroyed(&self) -> bool

Returns whether self 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.

⚠️ The following code is in C ⚠️

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.

⚠️ The following code is in C ⚠️

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.