gpu: Allow fences to check whether a flush has occurred

ui/gl/gl_context.cc

Index: ui/gl/gl_context.cc
diff --git a/ui/gl/gl_context.cc b/ui/gl/gl_context.cc
index cd9a28c387dcfabd66c18b7ccf7bbd3b88c3ff44..d7e6695bf98570b8611e77d25dd68bea867176e0 100644
--- a/ui/gl/gl_context.cc
+++ b/ui/gl/gl_context.cc
@@ -26,6 +26,20 @@ 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;
@@ -40,6 +54,13 @@ GLContext::~GLContext() {
   }
 }
 
+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;
@@ -172,6 +193,12 @@ 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) {}