High resolution timer fix for Windows

base/message_loop/incoming_task_queue.cc

Index: base/message_loop/incoming_task_queue.cc
diff --git a/base/message_loop/incoming_task_queue.cc b/base/message_loop/incoming_task_queue.cc
index bcc712b4a5d981b222b7a5ae4cbe84f9b67493e8..2049f491323a853784a8952c805a95494c894876 100644
--- a/base/message_loop/incoming_task_queue.cc
+++ b/base/message_loop/incoming_task_queue.cc
@@ -8,12 +8,14 @@
 #include "base/location.h"
 #include "base/message_loop/message_loop.h"
 #include "base/synchronization/waitable_event.h"
+#include "base/time/time.h"
 
 namespace base {
 namespace internal {
 
 IncomingTaskQueue::IncomingTaskQueue(MessageLoop* message_loop)
-    : message_loop_(message_loop),
+    : high_res_task_count_(0),
+      message_loop_(message_loop),
       next_sequence_num_(0) {
 }
 
@@ -25,15 +27,21 @@ bool IncomingTaskQueue::AddToIncomingQueue(
   AutoLock locked(incoming_queue_lock_);
   PendingTask pending_task(
       from_here, task, CalculateDelayedRuntime(delay), nestable);
+#if defined(OS_WIN)
+  // We consider the task needs a high resolution timer if the delay is
+  // more than 0 and less than 32ms.

[darin (slow to review), 2014/07/18 04:07:58]

why 32ms?

[jamesr, 2014/07/18 04:45:37]

the old comment justified this by saying that this caps the relative error of
the sleep to <50% (i.e. want a sleep of 33 but get one of 33+15=48 ms).  I'm not
super sure about that but this preserves the intended behavior - it'll be a lot
easier to figure out if and how to tweak this number when the logic works

[cpu_(ooo_6.6-7.5), 2014/07/18 22:53:10]

Added the math example to the comment.

This is an interesting knob to tweak, if we can get appropriate / reliable power
metrics. Audio tight audio timelines are around 6ms and thigh video timelines
are 16ms.

+  if (delay > TimeDelta() &&
+      delay.InMilliseconds() < (2 * Time::kMinLowResolutionThresholdMs)) {
+    ++high_res_task_count_;
+    pending_task.is_high_res = true;
+  }
+#endif
   return PostPendingTask(&pending_task);
 }
 
-bool IncomingTaskQueue::IsHighResolutionTimerEnabledForTesting() {
-#if defined(OS_WIN)
-  return !high_resolution_timer_expiration_.is_null();
-#else
-  return true;
-#endif
+bool IncomingTaskQueue::HasHighResolutionTasks() {
+  AutoLock lock(incoming_queue_lock_);
+  return (high_res_task_count_ > 0);

[darin (slow to review), 2014/07/18 04:07:58]

nit: unnecessary parens.

[cpu_(ooo_6.6-7.5), 2014/07/18 22:53:10]

Done.

 }
 
 bool IncomingTaskQueue::IsIdleForTesting() {
@@ -41,29 +49,22 @@ bool IncomingTaskQueue::IsIdleForTesting() {
   return incoming_queue_.empty();
 }
 
-void IncomingTaskQueue::ReloadWorkQueue(TaskQueue* work_queue) {
+int IncomingTaskQueue::ReloadWorkQueue(TaskQueue* work_queue) {
   // Make sure no tasks are lost.
   DCHECK(work_queue->empty());
 
   // Acquire all we can from the inter-thread queue with one lock acquisition.
   AutoLock lock(incoming_queue_lock_);
   if (!incoming_queue_.empty())
-    incoming_queue_.Swap(work_queue);  // Constant time
+    incoming_queue_.Swap(work_queue);
 
-  DCHECK(incoming_queue_.empty());
+  // Reset the count of high resolution tasks since our queue is now empty.
+  int high_res_tasks = high_res_task_count_;
+  high_res_task_count_ = 0;
+  return high_res_tasks;
 }
 
 void IncomingTaskQueue::WillDestroyCurrentMessageLoop() {
-#if defined(OS_WIN)
-  // If we left the high-resolution timer activated, deactivate it now.
-  // Doing this is not-critical, it is mainly to make sure we track
-  // the high resolution timer activations properly in our unit tests.
-  if (!high_resolution_timer_expiration_.is_null()) {
-    Time::ActivateHighResolutionTimer(false);
-    high_resolution_timer_expiration_ = TimeTicks();
-  }
-#endif
-
   AutoLock lock(incoming_queue_lock_);
   message_loop_ = NULL;
 }
@@ -75,40 +76,10 @@ IncomingTaskQueue::~IncomingTaskQueue() {
 
 TimeTicks IncomingTaskQueue::CalculateDelayedRuntime(TimeDelta delay) {
   TimeTicks delayed_run_time;
-  if (delay > TimeDelta()) {
+  if (delay > TimeDelta())
     delayed_run_time = TimeTicks::Now() + delay;
-
-#if defined(OS_WIN)
-    if (high_resolution_timer_expiration_.is_null()) {
-      // Windows timers are granular to 15.6ms.  If we only set high-res
-      // timers for those under 15.6ms, then a 18ms timer ticks at ~32ms,
-      // which as a percentage is pretty inaccurate.  So enable high
-      // res timers for any timer which is within 2x of the granularity.
-      // This is a tradeoff between accuracy and power management.
-      bool needs_high_res_timers = delay.InMilliseconds() <
-          (2 * Time::kMinLowResolutionThresholdMs);
-      if (needs_high_res_timers) {
-        if (Time::ActivateHighResolutionTimer(true)) {
-          high_resolution_timer_expiration_ = TimeTicks::Now() +
-              TimeDelta::FromMilliseconds(
-                  MessageLoop::kHighResolutionTimerModeLeaseTimeMs);
-        }
-      }
-    }
-#endif
-  } else {
+  else
     DCHECK_EQ(delay.InMilliseconds(), 0) << "delay should not be negative";
-  }
-
-#if defined(OS_WIN)
-  if (!high_resolution_timer_expiration_.is_null()) {
-    if (TimeTicks::Now() > high_resolution_timer_expiration_) {
-      Time::ActivateHighResolutionTimer(false);
-      high_resolution_timer_expiration_ = TimeTicks();
-    }
-  }
-#endif
-
   return delayed_run_time;
 }