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+// Copyright 2008, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//    * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//    * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//    * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef BASE_LOCK_H__
+#define BASE_LOCK_H__
+
+#include "base/lock_impl.h"
+
+// A convenient wrapper for a critical section.
+//
+// NOTE: A thread may acquire the same lock multiple times, but it must call
+// Release for each call to Acquire in order to finally release the lock.
+//
+// Complication: UnitTest for DeathTests catch DCHECK exceptions, so we need
+// to write code assuming DCHECK will throw.  This means we need to save any
+// assertable value in a local until we can safely throw.
+class Lock {
+ public:
+  Lock();
+  ~Lock();
+  void Acquire();
+  void Release();
+  // If the lock is not held, take it and return true. If the lock is already
+  // held by something else, immediately return false.
+  bool Try();
+
+ private:
+  LockImpl lock_;  // User-supplied underlying lock implementation.
+
+  // All private data is implicitly protected by spin_lock_.
+  // Be VERY careful to only access under that lock.
+  int32 recursion_count_shadow_;
+
+  // Allow access to GetCurrentThreadRecursionCount()
+  friend class AutoUnlock;
+  int32 GetCurrentThreadRecursionCount();
+
+#ifndef NDEBUG
+  // Even in Debug mode, the expensive tallies won't be calculated by default.
+  bool recursion_used_;
+  int32 acquisition_count_;
+
+  int32 contention_count_;
+#endif  // NDEBUG
+
+  DISALLOW_EVIL_CONSTRUCTORS(Lock);
+};
+
+// A helper class that acquires the given Lock while the AutoLock is in scope.
+class AutoLock {
+ public:
+  AutoLock(Lock& lock) : lock_(lock) {
+    lock_.Acquire();
+  }
+
+  ~AutoLock() {
+    lock_.Release();
+  }
+
+ private:
+  Lock& lock_;
+  DISALLOW_EVIL_CONSTRUCTORS(AutoLock);
+};
+
+// A helper macro to perform a single operation (expressed by expr)
+// in a lock
+#define LOCKED_EXPRESSION(lock, expr) \
+  do { \
+    AutoLock _auto_lock(lock);  \
+    (expr); \
+  } while (0)
+
+// AutoUnlock is a helper class for ConditionVariable instances
+// that is analogous to AutoLock.  It provides for nested Releases
+// of a lock for the Wait functionality of a ConditionVariable class.
+// The destructor automatically does the corresponding Acquire
+// calls (to return to the initial nested lock state).
+
+// Instances of AutoUnlock can ***ONLY*** validly be constructed if the
+// caller currently holds the lock provided as the constructor's argument.
+// If that ***REQUIREMENT*** is violated in debug mode, a DCHECK will
+// be generated in the Lock class.  In production (non-debug),
+// the results are undefined (and probably bad) if the caller
+// is not already holding the indicated lock.
+class ConditionVariable;
+class AutoUnlock {
+ private:  // Everything is private, so only our friend can use us.
+  friend class ConditionVariable;  // The only user of this class.
+  explicit AutoUnlock(Lock& lock);
+  ~AutoUnlock();
+
+  Lock* lock_;
+  int release_count_;
+};
+
+#endif  // BASE_LOCK_H__