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 // 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 BASE_SEQUENCE_CHECKER_IMPL_H_

 #define BASE_SEQUENCE_CHECKER_IMPL_H_

 #include "base/base_export.h"

 #include "base/basictypes.h"

 #include "base/synchronization/lock.h"

 #include "base/threading/sequenced_worker_pool.h"

 #include "base/threading/thread_checker_impl.h"

 namespace base {

 // SequenceCheckerImpl is used to help verify that some methods of a

 // class are called in sequence -- that is, called from the same

 // SequencedTaskRunner. It is a generalization of ThreadChecker; in

 // particular, it behaves exactly like ThreadChecker if constructed

 // on a thread that is not part of a SequencedWorkerPool.

 class BASE_EXPORT SequenceCheckerImpl {

  public:

   SequenceCheckerImpl();

   ~SequenceCheckerImpl();

   // Returns whether the we are being called on the same sequence token

   // as previous calls. If there is no associated sequence, then returns

   // whether we are being called on the underlying ThreadChecker's thread.

   bool CalledOnValidSequencedThread() const;

   // Unbinds the checker from the currently associated sequence. The

   // checker will be re-bound on the next call to CalledOnValidSequence().

   void DetachFromSequence();

  private:

   void EnsureSequenceTokenAssigned() const;

   // Guards all variables below.

   mutable Lock lock_;

   // Used if |sequence_token_| is not valid.

   ThreadCheckerImpl thread_checker_;

   mutable bool sequence_token_assigned_;

   mutable SequencedWorkerPool::SequenceToken sequence_token_;

   DISALLOW_COPY_AND_ASSIGN(SequenceCheckerImpl);

 };

 }  // namespace base

 #endif  // BASE_SEQUENCE_CHECKER_IMPL_H_