gpu: Allow fences to check whether a flush has occurred

ui/gl/gl_context.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 <string>
 
 #include "base/command_line.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/threading/thread_local.h"
 #include "ui/gl/gl_bindings.h"
 #include "ui/gl/gl_context.h"
 #include "ui/gl/gl_gl_api_implementation.h"
 #include "ui/gl/gl_implementation.h"
 #include "ui/gl/gl_surface.h"
 #include "ui/gl/gl_switches.h"
 #include "ui/gl/gl_version_info.h"
 
 namespace gfx {
 
 namespace {
 base::LazyInstance<base::ThreadLocalPointer<GLContext> >::Leaky
     current_context_ = LAZY_INSTANCE_INITIALIZER;
 
 base::LazyInstance<base::ThreadLocalPointer<GLContext> >::Leaky
     current_real_context_ = LAZY_INSTANCE_INITIALIZER;
 }  // namespace
 
+GLContext::FlushEvent::FlushEvent() : state_(0) {
+}
+
+GLContext::FlushEvent::~FlushEvent() {
+}
+
+void GLContext::FlushEvent::Signal() {
+  base::subtle::NoBarrier_AtomicExchange(&state_, 1);

[piman, 2014/03/15 00:18:40]

I'm not convinced whether this is correct or not.
Maybe we can reuse base::CancellationFlag that has the same semantics, but is
well tested?

[no sievers, 2014/03/19 01:25:21]

Done.

+}
+
+bool GLContext::FlushEvent::IsSignaled() {
+  return base::subtle::NoBarrier_CompareAndSwap(&state_, 1, 1) != 0;
+}
+
 GLContext::GLContext(GLShareGroup* share_group) : share_group_(share_group) {
   if (!share_group_.get())
     share_group_ = new GLShareGroup;
 
   share_group_->AddContext(this);
 }
 
 GLContext::~GLContext() {
   share_group_->RemoveContext(this);
   if (GetCurrent() == this) {
     SetCurrent(NULL);
   }
 }
 
+scoped_refptr<GLContext::FlushEvent>
+GLContext::SignalFlush() {
+  scoped_refptr<FlushEvent> flush_event = new FlushEvent();
+  flush_events_.push_back(flush_event);
+  return flush_event;
+}
+
 bool GLContext::GetTotalGpuMemory(size_t* bytes) {
   DCHECK(bytes);
   *bytes = 0;
   return false;
 }
 
 void GLContext::SetSafeToForceGpuSwitch() {
 }
 
 void GLContext::SetUnbindFboOnMakeCurrent() {
@@ skipping 112 matching lines @@
 
 void GLContext::OnReleaseVirtuallyCurrent(GLContext* virtual_context) {
   if (virtual_gl_api_)
     virtual_gl_api_->OnReleaseVirtuallyCurrent(virtual_context);
 }
 
 void GLContext::SetRealGLApi() {
   SetGLToRealGLApi();
 }
 
+void GLContext::OnFlush() {
+  for (size_t n = 0; n < flush_events_.size(); n++)
+    flush_events_[n]->Signal();
+  flush_events_.clear();
+}
+
 GLContextReal::GLContextReal(GLShareGroup* share_group)
     : GLContext(share_group) {}
 
 GLContextReal::~GLContextReal() {}
 
 void GLContextReal::SetCurrent(GLSurface* surface) {
   GLContext::SetCurrent(surface);
   current_real_context_.Pointer()->Set(surface ? this : NULL);
 }
 
 }  // namespace gfx