content/gpu: Simplify stub scheduling.

gpu/command_buffer/service/gpu_scheduler.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "gpu/command_buffer/service/gpu_scheduler.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/compiler_specific.h"
 #include "base/message_loop/message_loop.h"
@@ skipping 16 matching lines @@
 const int64 kRescheduleTimeOutDelay = 1000;
 #endif
 
 GpuScheduler::GpuScheduler(CommandBufferServiceBase* command_buffer,
                            AsyncAPIInterface* handler,
                            gles2::GLES2Decoder* decoder)
     : command_buffer_(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(
      "gpu", "GpuScheduler:PutChanged",
      "decoder", decoder_ ? decoder_->GetLogger()->GetLogPrefix() : "None");
 
   CommandBuffer::State state = command_buffer_->GetLastState();
 
   // If there is no parser, exit.
   if (!parser_.get()) {
@@ skipping 52 matching lines @@
     decoder_->EndDecoding();
     decoder_->AddProcessingCommandsTime(base::TimeTicks::Now() - begin_time);
   }
 }
 
 void GpuScheduler::SetScheduled(bool scheduled) {
   TRACE_EVENT2("gpu", "GpuScheduler:SetScheduled", "this", this,
                "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() {
   return unscheduled_count_ == 0;
 }
 
 bool GpuScheduler::HasMoreWork() {
   return (decoder_ && decoder_->ProcessPendingQueries(false)) ||
          HasMoreIdleWork();
 }
@@ skipping 64 matching lines @@
 bool GpuScheduler::HasMoreIdleWork() {
   return (decoder_ && decoder_->HasMoreIdleWork());
 }
 
 void GpuScheduler::PerformIdleWork() {
   if (!decoder_)
     return;
   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