SyncPointManager never returns 0.

content/common/gpu/sync_point_manager.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 "content/common/gpu/sync_point_manager.h"
 
 #include <climits>
 
 #include "base/logging.h"
 #include "base/rand_util.h"
 
 namespace content {
 
 static const int kMaxSyncBase = INT_MAX;
 
 SyncPointManager::SyncPointManager()
     : next_sync_point_(base::RandInt(1, kMaxSyncBase)) {
   // To reduce the risk that a sync point created in a previous GPU process
   // will be in flight in the next GPU process, randomize the starting sync
   // point number. http://crbug.com/373452
 }
 
 SyncPointManager::~SyncPointManager() {
 }
 
 uint32 SyncPointManager::GenerateSyncPoint() {
   base::AutoLock lock(lock_);
   uint32 sync_point = next_sync_point_++;
+  // When an integer overflow occurs, don't return 0.
+  if (!sync_point)
+    sync_point = next_sync_point_++;
 
   // Note: wrapping would take days for a buggy/compromized renderer that would
   // insert sync points in a loop, but if that were to happen, better explicitly
   // crash the GPU process than risk worse.
   // For normal operation (at most a few per frame), it would take ~a year to
   // wrap.
   CHECK(sync_point_map_.find(sync_point) == sync_point_map_.end());
   sync_point_map_.insert(std::make_pair(sync_point, ClosureList()));
   return sync_point;
 }
@@ skipping 29 matching lines @@
 bool SyncPointManager::IsSyncPointRetired(uint32 sync_point) {
   DCHECK(thread_checker_.CalledOnValidThread());
   {
     base::AutoLock lock(lock_);
     SyncPointMap::iterator it = sync_point_map_.find(sync_point);
     return it == sync_point_map_.end();
   }
 }
 
 }  // namespace content