SyncPointManager never returns 0.

content/common/gpu/sync_point_manager.h

 // 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.
 
 #ifndef CONTENT_COMMON_GPU_SYNC_POINT_MANAGER_H_
 #define CONTENT_COMMON_GPU_SYNC_POINT_MANAGER_H_
 
 #include <vector>
 
 #include "base/callback.h"
 #include "base/containers/hash_tables.h"
 #include "base/memory/ref_counted.h"
 #include "base/synchronization/lock.h"
 #include "base/threading/thread_checker.h"
 
 namespace content {
 
 // This class manages the sync points, which allow cross-channel
 // synchronization.
 class SyncPointManager : public base::RefCountedThreadSafe<SyncPointManager> {
  public:
   SyncPointManager();
 
   // Generates a sync point, returning its ID. This can me called on any thread.
-  // IDs start at 1.
+  // IDs start at a random number. Never return 0.
   uint32 GenerateSyncPoint();
 
   // Retires a sync point. This will call all the registered callbacks for this
   // sync point. This can only be called on the main thread.
   void RetireSyncPoint(uint32 sync_point);
 
   // Adds a callback to the sync point. The callback will be called when the
   // sync point is retired, or immediately (from within that function) if the
   // sync point was already retired (or not created yet). This can only be
   // called on the main thread.
@@ skipping 15 matching lines @@
   base::Lock lock_;
   SyncPointMap sync_point_map_;
   uint32 next_sync_point_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncPointManager);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_COMMON_GPU_SYNC_POINT_MANAGER_H_