MetaIdleMonitor: fire immediately watches that are already expired

The XSync semantics mandate that alarms already expired will not
fire until the counter is reset and the alarm triggered again, so
clients traditionally called get_idle_time() first to see if they
should install the alarm.
This is inherently racy, as by the time the call is handled by
mutter and the reply received the idle time could be different.
Instead, if we see that the watch would have fired in the past,
fire it immediately.

This is a behavior change, but it's a compatible one, as all legacy
clients are calling get_idle_time() first, and it was perfectly
possible for the idle time counter to trigger the alarm right
after the get_idle_time() call.

https://bugzilla.gnome.org/show_bug.cgi?id=707302

1 files changed, 28 insertions, 1 deletions

diff --git a/src/core/meta-idle-monitor.c b/src/core/meta-idle-monitor.c
index 00b6ddb8e..d351e65a9 100644
--- a/src/core/meta-idle-monitor.c
+++ b/src/core/meta-idle-monitor.c
@@ -74,7 +74,8 @@ typedef struct
   guint64                   timeout_msec;
 
   /* x11 */
-  XSyncAlarm	            xalarm;
+  XSyncAlarm                xalarm;
+  int                       idle_source_id;
 } MetaIdleMonitorWatch;
 
 enum
@@ -110,6 +111,12 @@ fire_watch (MetaIdleMonitorWatch *watch)
   monitor = watch->monitor;
   g_object_ref (monitor);
 
+  if (watch->idle_source_id)
+    {
+      g_source_remove (watch->idle_source_id);
+      watch->idle_source_id = 0;
+    }
+
   id = watch->id;
   is_user_active_watch = (watch->timeout_msec == 0);
 
@@ -281,6 +288,12 @@ idle_monitor_watch_free (MetaIdleMonitorWatch *watch)
 
   monitor = watch->monitor;
 
+  if (watch->idle_source_id)
+    {
+      g_source_remove (watch->idle_source_id);
+      watch->idle_source_id = 0;
+    }
+
   if (watch->notify != NULL)
     watch->notify (watch->user_data);
 
@@ -449,6 +462,17 @@ meta_idle_monitor_get_for_device (int device_id)
   return device_monitors[device_id];
 }
 
+static gboolean
+fire_watch_idle (gpointer data)
+{
+  MetaIdleMonitorWatch *watch = data;
+
+  watch->idle_source_id = 0;
+  fire_watch (watch);
+
+  return FALSE;
+}
+
 static MetaIdleMonitorWatch *
 make_watch (MetaIdleMonitor           *monitor,
             guint64                    timeout_msec,
@@ -471,6 +495,9 @@ make_watch (MetaIdleMonitor           *monitor,
       watch->xalarm = _xsync_alarm_set (monitor, XSyncPositiveTransition, timeout_msec, TRUE);
 
       g_hash_table_add (monitor->alarms, (gpointer) watch->xalarm);
+
+      if (meta_idle_monitor_get_idletime (monitor) > (gint64)timeout_msec)
+        watch->idle_source_id = g_idle_add (fire_watch_idle, watch);
     }
   else
     {