gpu: Use explicit atomics instead of assuming that 32bit read/writes are atomic.

gpu/command_buffer/client/query_tracker.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/client/query_tracker.h"
 
 #include <GLES2/gl2.h>
 #include <GLES2/gl2ext.h>
 #include <GLES2/gl2extchromium.h>
 
+#include "base/atomicops.h"
 #include "gpu/command_buffer/client/gles2_cmd_helper.h"
 #include "gpu/command_buffer/client/gles2_implementation.h"
 #include "gpu/command_buffer/client/mapped_memory.h"
 #include "gpu/command_buffer/common/time.h"
 
 namespace gpu {
 namespace gles2 {
 
 QuerySyncManager::QuerySyncManager(MappedMemoryManager* manager)
     : mapped_memory_(manager) {
@@ skipping 118 matching lines @@
       }
     }
   }
   gl->helper()->EndQueryEXT(target(), submit_count());
   MarkAsPending(gl->helper()->InsertToken());
 }
 
 bool QueryTracker::Query::CheckResultsAvailable(
     CommandBufferHelper* helper) {
   if (Pending()) {
-    if (info_.sync->process_count == submit_count_ ||
+    if (base::subtle::Acquire_Load(&info_.sync->process_count) ==
+            submit_count_ ||
         helper->IsContextLost()) {
-      // Need a MemoryBarrier here so that sync->result read after
-      // sync->process_count.
-      base::subtle::MemoryBarrier();
       switch (target()) {
         case GL_COMMANDS_ISSUED_CHROMIUM:
           result_ = std::min(info_.sync->result,
                              static_cast<uint64>(0xFFFFFFFFL));
           break;
         case GL_LATENCY_QUERY_CHROMIUM:
           DCHECK(info_.sync->result >= client_begin_time_us_);
           result_ = std::min(info_.sync->result - client_begin_time_us_,
                              static_cast<uint64>(0xFFFFFFFFL));
           break;
@@ skipping 78 matching lines @@
 void QueryTracker::Shrink() {
   FreeCompletedQueries();
   query_sync_manager_.Shrink();
 }
 
 void QueryTracker::FreeCompletedQueries() {
   QueryList::iterator it = removed_queries_.begin();
   while (it != removed_queries_.end()) {
     Query* query = *it;
     if (query->Pending() &&
-        query->info_.sync->process_count != query->submit_count()) {
+        base::subtle::Acquire_Load(&query->info_.sync->process_count) !=
+            query->submit_count()) {
       ++it;
       continue;
     }
 
     query_sync_manager_.Free(query->info_);
     it = removed_queries_.erase(it);
     delete query;
   }
 }
 
 }  // namespace gles2
 }  // namespace gpu