systemclock: fix multi-thread entry status issue

Running two threads, one executing the timer and one unscheduling it, the
unscheduled status set by the second thread is sometimes overwritten by the
first one.

https://bugzilla.gnome.org/show_bug.cgi?id=737999

diff --git a/gst/gstsystemclock.c b/gst/gstsystemclock.c
index dabce1d..3071926 100644 (file)
--- a/gst/gstsystemclock.c
+++ b/gst/gstsystemclock.c
@@ -637,7 +637,8 @@ gst_system_clock_id_wait_jitter_unlocked (GstClock * clock,
   GstClockTimeDiff diff;
   GstClockReturn status;
 
-  if (G_UNLIKELY (GET_ENTRY_STATUS (entry) == GST_CLOCK_UNSCHEDULED))
+  status = GET_ENTRY_STATUS (entry);
+  if (G_UNLIKELY (status == GST_CLOCK_UNSCHEDULED))
     return GST_CLOCK_UNSCHEDULED;
 
   /* need to call the overridden method because we want to sync against the time
@@ -737,8 +738,13 @@ gst_system_clock_id_wait_jitter_unlocked (GstClock * clock,
 
         if (diff <= 0) {
           /* timeout, this is fine, we can report success now */
-          status = GST_CLOCK_OK;
-          SET_ENTRY_STATUS (entry, status);
+          if (G_UNLIKELY (!CAS_ENTRY_STATUS (entry, GST_CLOCK_DONE, GST_CLOCK_OK))) {
+            GST_CAT_DEBUG (GST_CAT_CLOCK, "unexpected status for entry %p", entry);
+            status = GET_ENTRY_STATUS (entry);
+            goto done;
+          } else {
+            status = GST_CLOCK_OK;
+          }
 
           GST_CAT_DEBUG (GST_CAT_CLOCK,
               "entry %p finished, diff %" G_GINT64_FORMAT, entry, diff);
@@ -762,12 +768,21 @@ gst_system_clock_id_wait_jitter_unlocked (GstClock * clock,
     }
   } else {
     /* we are right on time or too late */
-    if (G_UNLIKELY (diff == 0))
-      status = GST_CLOCK_OK;
-    else
-      status = GST_CLOCK_EARLY;
-
-    SET_ENTRY_STATUS (entry, status);
+    if (G_UNLIKELY (diff == 0)) {
+      if (G_UNLIKELY (!CAS_ENTRY_STATUS (entry, status, GST_CLOCK_OK))) {
+        GST_CAT_DEBUG (GST_CAT_CLOCK, "unexpected status for entry %p", entry);
+        status = GET_ENTRY_STATUS (entry);
+      } else {
+        status = GST_CLOCK_OK;
+      }
+    } else {
+      if (G_UNLIKELY (!CAS_ENTRY_STATUS (entry, status, GST_CLOCK_EARLY))) {
+        GST_CAT_DEBUG (GST_CAT_CLOCK, "unexpected status for entry %p", entry);
+        status = GET_ENTRY_STATUS (entry);
+      } else {
+        status = GST_CLOCK_EARLY;
+      }
+    }
   }
 done:
   return status;