Process pending delayed tasks in kMsgHaveWork

base/message_loop/message_pump_win.cc

Index: base/message_loop/message_pump_win.cc
diff --git a/base/message_loop/message_pump_win.cc b/base/message_loop/message_pump_win.cc
index 27b47e1a0f878cfceef3c04b2364116ca64ac4c8..f3faccfee810c0e6e2ac91db75f0f791304a87cd 100644
--- a/base/message_loop/message_pump_win.cc
+++ b/base/message_loop/message_pump_win.cc
@@ -146,20 +146,24 @@ void MessagePumpForUI::ScheduleDelayedWork(const TimeTicks& delayed_work_time) {
 
   int delay_msec = GetCurrentDelay();
   DCHECK_GE(delay_msec, 0);
-  if (delay_msec < USER_TIMER_MINIMUM)
-    delay_msec = USER_TIMER_MINIMUM;
-
-  // Create a WM_TIMER event that will wake us up to check for any pending
-  // timers (in case we are running within a nested, external sub-pump).
-  BOOL ret = SetTimer(message_hwnd_, reinterpret_cast<UINT_PTR>(this),
-                      delay_msec, NULL);
-  if (ret)
-    return;
-  // If we can't set timers, we are in big trouble... but cross our fingers for
-  // now.
-  // TODO(jar): If we don't see this error, use a CHECK() here instead.
-  UMA_HISTOGRAM_ENUMERATION("Chrome.MessageLoopProblem", SET_TIMER_ERROR,
-                            MESSAGE_LOOP_PROBLEM_MAX);
+  if (delay_msec == 0) {
+    ScheduleWork();
+  } else {
+    if (delay_msec < USER_TIMER_MINIMUM)
+      delay_msec = USER_TIMER_MINIMUM;
+
+    // Create a WM_TIMER event that will wake us up to check for any pending
+    // timers (in case we are running within a nested, external sub-pump).
+    BOOL ret = SetTimer(message_hwnd_, reinterpret_cast<UINT_PTR>(this),
+                        delay_msec, NULL);
+    if (ret)
+      return;
+    // If we can't set timers, we are in big trouble... but cross our fingers
+    // for now.
+    // TODO(jar): If we don't see this error, use a CHECK() here instead.
+    UMA_HISTOGRAM_ENUMERATION("Chrome.MessageLoopProblem", SET_TIMER_ERROR,
+                              MESSAGE_LOOP_PROBLEM_MAX);
+  }
 }
 
 //-----------------------------------------------------------------------------
@@ -318,6 +322,11 @@ void MessagePumpForUI::HandleWorkMessage() {
   // needs to do more work.
   if (state_->delegate->DoWork())
     ScheduleWork();
+  state_->delegate->DoDelayedWork(&delayed_work_time_);

[jar (doing other things), 2015/05/13 20:01:21]

Note that you *might* effectively double the amount of work (number of tasks)
done during each HandleWorkMessage.  Worse yet, it might actually swell up the
regular task queue during an "overload," rather than "do less work" when we fall
behind.  The cases where this is crucial are indeed very sensitive to resulting
jank (due to CPU usage).

The only reason (I think) for this HandleWorkMessage method to run is that we're
in a nested (native?) message loop, and not getting to run our traditional list
of chores (which do include both a shot at regular tasks, as well as delayed
tasks).  In that nested-loop situation, it is commonly the case that the OS
really wants to tightly control responsiveness (which is why they ran a tight
native loop)... so we only very intermittently run a Chrome Task.  We
deliberately allow them to get progressively more cycles (proportionately) if
they are processing a pile of native queue messages.

Perhaps we should change lines 323/324 to:

 if (state_->delegate->DoWork()) {
   ScheduleWork();
   return;  // We did absolutely minimal amount of work.
  }
  // Fallthrough to see if DelayedWork needs to be done.


You could argue that we should randomly try DoDelayedWork vs DoWork... and
perhaps that could be crafted in here.

IMO, a more common case would be that a delayed task fires, and it posts a bunch
of tasks (or tasks that post tasks), and it is probably better to handle most
all of those "first" (or at least ASAP), rather than doing some more delayed
tasks "sooner" and perhaps REALLY growing our regular task queue.

+  if (!delayed_work_time_.is_null()) {
+    // A bit gratuitous to set delayed_work_time_ again, but oh well.
+    ScheduleDelayedWork(delayed_work_time_);
+  }
 }
 
 void MessagePumpForUI::HandleTimerMessage() {