[glib/wip/pwithnall/local-file-monitor-deadlock] glocalfilemonitor: Avoid a deadlock on finalization

[Philip Withnall <pwithnall src gnome org>]

commit 838dc04c7674a197d3085ff785e13cd440324002
Author: Philip Withnall <pwithnall endlessos org>
Date:   Mon Jun 14 15:02:59 2021 +0100

    glocalfilemonitor: Avoid a deadlock on finalization
    
    If `g_file_monitor_source_dispatch()` drops the last reference to its
    `GLocalFileMonitor`, a deadlock will occur, because disposing the
    `GLocalFileMonitor` causes synchronous disposal of the
    `GFileMonitorSource`, and hence an attempt to re-lock the already-locked
    mutex in the `GFileMonitorSource`.
    
    Fix that by dropping the reference to the `GLocalFileMonitor` after
    unlocking.
    
    Diagnosed by Ting-Wei Lan. The bug was originally introduced by me in
    commit 592a13b483.
    
    Signed-off-by: Philip Withnall <pwithnall endlessos org>

 gio/glocalfilemonitor.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/gio/glocalfilemonitor.c b/gio/glocalfilemonitor.c
index eccab231c..dc32fb660 100644
--- a/gio/glocalfilemonitor.c
+++ b/gio/glocalfilemonitor.c
@@ -555,8 +555,8 @@ g_file_monitor_source_dispatch (GSource     *source,
 
   g_file_monitor_source_update_ready_time (fms);
 
-  g_clear_object (&instance);
   g_mutex_unlock (&fms->lock);
+  g_clear_object (&instance);
 
   /* We now have our list of events to deliver */
   while ((event = g_queue_pop_head (&event_queue)))