content/gpu: Simplify stub scheduling.

gpu/command_buffer/service/gpu_scheduler.cc

Index: gpu/command_buffer/service/gpu_scheduler.cc
diff --git a/gpu/command_buffer/service/gpu_scheduler.cc b/gpu/command_buffer/service/gpu_scheduler.cc
index 2a15dc76f9c06d14914f5b2470a5c758f8eeeb4e..75ce9c4f6cea7fa83ec1571c8a52350734d203a4 100644
--- a/gpu/command_buffer/service/gpu_scheduler.cc
+++ b/gpu/command_buffer/service/gpu_scheduler.cc
@@ -34,12 +34,9 @@ GpuScheduler::GpuScheduler(CommandBufferServiceBase* command_buffer,
       handler_(handler),
       decoder_(decoder),
       unscheduled_count_(0),
-      rescheduled_count_(0),
-      was_preempted_(false),
-      reschedule_task_factory_(this) {}
+      was_preempted_(false) {}
 
-GpuScheduler::~GpuScheduler() {
-}
+GpuScheduler::~GpuScheduler() {}
 
 void GpuScheduler::PutChanged() {
   TRACE_EVENT1(
@@ -112,49 +109,15 @@ void GpuScheduler::SetScheduled(bool scheduled) {
                "new unscheduled_count_",
                unscheduled_count_ + (scheduled? -1 : 1));
   if (scheduled) {
-    // If the scheduler was rescheduled after a timeout, ignore the subsequent
-    // calls to SetScheduled when they eventually arrive until they are all
-    // accounted for.
-    if (rescheduled_count_ > 0) {
-      --rescheduled_count_;
-      return;
-    } else {
-      --unscheduled_count_;
-    }
-
-    DCHECK_GE(unscheduled_count_, 0);
-
-    if (unscheduled_count_ == 0) {
-      TRACE_EVENT_ASYNC_END1("gpu", "ProcessingSwap", this,
-                             "GpuScheduler", this);
-      // When the scheduler transitions from the unscheduled to the scheduled
-      // state, cancel the task that would reschedule it after a timeout.
-      reschedule_task_factory_.InvalidateWeakPtrs();
-
-      if (!scheduling_changed_callback_.is_null())
+    --unscheduled_count_;
+    if (unscheduled_count_ == 0 && !scheduling_changed_callback_.is_null())
         scheduling_changed_callback_.Run(true);
-    }
   } else {
     ++unscheduled_count_;
-    if (unscheduled_count_ == 1) {
-      TRACE_EVENT_ASYNC_BEGIN1("gpu", "ProcessingSwap", this,
-                               "GpuScheduler", this);
-#if defined(OS_WIN)
-      if (base::win::GetVersion() < base::win::VERSION_VISTA) {
-        // When the scheduler transitions from scheduled to unscheduled, post a
-        // delayed task that it will force it back into a scheduled state after
-        // a timeout. This should only be necessary on pre-Vista.
-        base::MessageLoop::current()->PostDelayedTask(
-            FROM_HERE,
-            base::Bind(&GpuScheduler::RescheduleTimeOut,
-                       reschedule_task_factory_.GetWeakPtr()),
-            base::TimeDelta::FromMilliseconds(kRescheduleTimeOutDelay));
-      }
-#endif

[piman, 2015/09/16 21:46:29]

What is the reason this is not needed any more? Is it because NPAPI is gone?
Not that I'm in love with this hack, but unless I'm confused, we still use the
browser's HWND, so we have synchronous win32 messages between this thread and
the browser's UI thread. Are we guaranteed cycles are gone?

[sunnyps, 2015/09/16 23:08:31]

I do not know what everything else looked like when this code was added but:
1. SetScheduled is *only* called by GpuCommandBufferStub when it waits for a
sync point and that use case certainly doesn't need a reschedule timeout.
2. When this code was added it was for all windows versions - in fact the
original bug was a crash when closing the page while youtube was running on
windows 7. crbug.com/111514
3. After some time it was found that this code was inconvenient for debugging
because a DCHECK triggers if you pause in the debugger so it was made XP only
because no developers use XP. crrev.com/12315112

-      if (!scheduling_changed_callback_.is_null())
+    if (unscheduled_count_ == 1 && !scheduling_changed_callback_.is_null())
         scheduling_changed_callback_.Run(false);
-    }
   }
+  DCHECK_GE(unscheduled_count_, 0);
 }
 
 bool GpuScheduler::IsScheduled() {
@@ -239,15 +202,4 @@ void GpuScheduler::PerformIdleWork() {
   decoder_->PerformIdleWork();
 }
 
-void GpuScheduler::RescheduleTimeOut() {
-  int new_count = unscheduled_count_ + rescheduled_count_;
-
-  rescheduled_count_ = 0;
-
-  while (unscheduled_count_)
-    SetScheduled(true);
-
-  rescheduled_count_ = new_count;
-}
-
 }  // namespace gpu