Make ShareGroup thread safe

gpu/command_buffer/client/atomicops.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 GPU_COMMAND_BUFFER_CLIENT_ATOMICOPS_H_
 #define GPU_COMMAND_BUFFER_CLIENT_ATOMICOPS_H_
 
+#include "../../gpu_export.h"
+#include "../common/scoped_ptr.h"
+#include "../common/types.h"
+
 namespace gpu {
 
 void MemoryBarrier();
 
+class LockImpl;
+class GPU_EXPORT Lock {
+ public:
+  Lock();
+  ~Lock();
+  void Acquire();
+  void Release();
+  bool Try();
+  void AssertAcquired() const;
+
+ private:
+  scoped_ptr<LockImpl> lock_;
+
+  DISALLOW_COPY_AND_ASSIGN(Lock);
+};
+
+// A helper class that acquires the given Lock while the AutoLock is in scope.
+class GPU_EXPORT AutoLock {
+ public:
+  explicit AutoLock(Lock& lock) : lock_(lock) {
+    lock_.Acquire();
+  }
+
+  ~AutoLock() {
+    lock_.AssertAcquired();

[apatrick_chromium, 2012/03/29 21:03:58]

What if another thread has the lock?

+    lock_.Release();
+  }
+
+ private:
+  Lock& lock_;
+  DISALLOW_COPY_AND_ASSIGN(AutoLock);
+};
+
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_CLIENT_ATOMICOPS_H_