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glocalfilemonitor: Skip event handling if the source has been destroyed

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This should prevent unbounded growth of the `event_queue` in the
unlikely case that the `GSource` is removed from its `GMainContext` and
destroyed separately from the `GFileMonitor`.

I’m not sure if that can currently happen, but it could with future
refactoring, so it’s best to address the possibility now while we’re
thinking about this bit of code.

Signed-off-by: Philip Withnall <pwithnall@endlessos.org>

Helps: #1941
This commit is contained in:
Philip Withnall 2022-05-30 17:54:18 +01:00
parent ee4d93c6fd
commit 8e9f238667
1 changed files with 23 additions and 6 deletions
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29
gio/glocalfilemonitor.c
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@ -360,11 +360,28 @@ g_file_monitor_source_handle_event (GFileMonitorSource *fms,
g_mutex_lock (&fms->lock);
/* NOTE: We process events even if the file monitor has already been disposed.
* The reason is that we must not take a reference to the instance here
* as destroying it from the event handling thread will lead to a
* deadlock when taking the lock in _ih_sub_cancel.
/* NOTE:
*
* We process events even if the file monitor has already been disposed.
* The reason is that we must not take a reference to the instance here as
* destroying it from the event handling thread will lead to a deadlock when
* taking the lock in _ih_sub_cancel.
*
* This results in seemingly-unbounded growth of the `event_queue` with the
* calls to `g_file_monitor_source_queue_event()`. However, each of those sets
* the ready time on the #GSource, which means that it will be dispatched in
* a subsequent iteration of the #GMainContext it’s attached to. At that
* point, `g_file_monitor_source_dispatch()` will return %FALSE, and this will
* trigger finalisation of the source. That will clear the `event_queue`.
*
* If the source is no longer attached, this will return early to prevent
* unbounded queueing.
*/
if (g_source_is_destroyed ((GSource *) fms))
{
g_mutex_unlock (&fms->lock);
return TRUE;
}
switch (event_type)
{
@ -597,9 +614,9 @@ g_file_monitor_source_dispose (GFileMonitorSource *fms)
g_file_monitor_source_update_ready_time (fms);
g_mutex_unlock (&fms->lock);
g_source_destroy ((GSource *) fms);
g_mutex_unlock (&fms->lock);
}
static void