Call MaybeScheduleNestingDeferredWork at the top of each loop iteration from

a kCFRunLoopBeforeSources observer.  A busy loop that's driven with a nonzero
duration might not go to sleep or exit soon after a nested loop exits, so
calling MaybeScheduleNestingDeferredWork from the existing
kCFRunLoopBeforeWaiting and kCFRunLoopExit observers may not be sufficient to
guarantee processing of nesting-deferred work in all situations.

BUG=24968
TEST=All of the test cases listed in the commit message from r29749.
     No new test cases; this change addresses a purely theoretical case.
Review URL: http://codereview.chromium.org/315010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@29775 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 10 insertions, 3 deletions

diff --git a/base/message_pump_mac.h b/base/message_pump_mac.h
index 9c24d8b..381acbf 100644
--- a/base/message_pump_mac.h
+++ b/base/message_pump_mac.h
@@ -97,9 +97,10 @@ class MessagePumpCFRunLoopBase : public MessagePump {
   bool RunNestingDeferredWork();
 
   // Schedules possible nesting-deferred work to be processed before the run
-  // loop goes to sleep or exits.  If this function detects that a nested loop
-  // had run since the previous attempt to schedule nesting-deferred work, it
-  // will schedule a call to RunNestingDeferredWorkSource.
+  // loop goes to sleep, exits, or begins processing sources at the top of its
+  // loop.  If this function detects that a nested loop had run since the
+  // previous attempt to schedule nesting-deferred work, it will schedule a
+  // call to RunNestingDeferredWorkSource.
   void MaybeScheduleNestingDeferredWork();
 
   // Observer callback responsible for performing idle-priority work, before
@@ -107,6 +108,11 @@ class MessagePumpCFRunLoopBase : public MessagePump {
   static void PreWaitObserver(CFRunLoopObserverRef observer,
                               CFRunLoopActivity activity, void* info);
 
+  // Observer callback called before the run loop processes any sources.
+  // Associated with pre_source_observer_.
+  static void PreSourceObserver(CFRunLoopObserverRef observer,
+                                CFRunLoopActivity activity, void* info);
+
   // Observer callback called when the run loop starts and stops, at the
   // beginning and end of calls to CFRunLoopRun.  This is used to maintain
   // nesting_level_.  Associated with enter_exit_observer_.
@@ -129,6 +135,7 @@ class MessagePumpCFRunLoopBase : public MessagePump {
   CFRunLoopSourceRef idle_work_source_;
   CFRunLoopSourceRef nesting_deferred_work_source_;
   CFRunLoopObserverRef pre_wait_observer_;
+  CFRunLoopObserverRef pre_source_observer_;
   CFRunLoopObserverRef enter_exit_observer_;
 
   // (weak) Delegate passed as an argument to the innermost Run call.