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+// Copyright (c) 2011 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_SYNCHRONIZATION_LOCK_H_
+#define BASE_SYNCHRONIZATION_LOCK_H_
+#pragma once
+
+#include "base/base_export.h"
+#include "base/synchronization/lock_impl.h"
+#include "base/threading/platform_thread.h"
+
+namespace base {
+
+// A convenient wrapper for an OS specific critical section. The only real
+// intelligence in this class is in debug mode for the support for the
+// AssertAcquired() method.
+class BASE_EXPORT Lock {
+ public:
+#if defined(NDEBUG) // Optimized wrapper implementation
+ Lock() : lock_() {}
+ ~Lock() {}
+ void Acquire() { lock_.Lock(); }
+ void Release() { lock_.Unlock(); }
+
+ // If the lock is not held, take it and return true. If the lock is already
+ // held by another thread, immediately return false. This must not be called
+ // by a thread already holding the lock (what happens is undefined and an
+ // assertion may fail).
+ bool Try() { return lock_.Try(); }
+
+ // Null implementation if not debug.
+ void AssertAcquired() const {}
+#else
+ Lock();
+ ~Lock() {}
+
+ // NOTE: Although windows critical sections support recursive locks, we do not
+ // allow this, and we will commonly fire a DCHECK() if a thread attempts to
+ // acquire the lock a second time (while already holding it).
+ void Acquire() {
+ lock_.Lock();
+ CheckUnheldAndMark();
+ }
+ void Release() {
+ CheckHeldAndUnmark();
+ lock_.Unlock();
+ }
+
+ bool Try() {
+ bool rv = lock_.Try();
+ if (rv) {
+ CheckUnheldAndMark();
+ }
+ return rv;
+ }
+
+ void AssertAcquired() const;
+#endif // NDEBUG
+
+#if defined(OS_POSIX)
+ // The posix implementation of ConditionVariable needs to be able
+ // to see our lock and tweak our debugging counters, as it releases
+ // and acquires locks inside of pthread_cond_{timed,}wait.
+ // Windows doesn't need to do this as it calls the Lock::* methods.
+ friend class ConditionVariable;
+#endif
+
+ private:
+#if !defined(NDEBUG)
+ // Members and routines taking care of locks assertions.
+ // Note that this checks for recursive locks and allows them
+ // if the variable is set. This is allowed by the underlying implementation
+ // on windows but not on Posix, so we're doing unneeded checks on Posix.
+ // It's worth it to share the code.
+ void CheckHeldAndUnmark();
+ void CheckUnheldAndMark();
+
+ // All private data is implicitly protected by lock_.
+ // Be VERY careful to only access members under that lock.
+
+ // Determines validity of owning_thread_id_. Needed as we don't have
+ // a null owning_thread_id_ value.
+ bool owned_by_thread_;
+ base::PlatformThreadId owning_thread_id_;
+#endif // NDEBUG
+
+ // Platform specific underlying lock implementation.
+ internal::LockImpl lock_;
+
+ DISALLOW_COPY_AND_ASSIGN(Lock);
+};
+
+// A helper class that acquires the given Lock while the AutoLock is in scope.
+class AutoLock {
+ public:
+ explicit AutoLock(Lock& lock) : lock_(lock) {
+ lock_.Acquire();
+ }
+
+ ~AutoLock() {
+ lock_.AssertAcquired();
+ lock_.Release();
+ }
+
+ private:
+ Lock& lock_;
+ DISALLOW_COPY_AND_ASSIGN(AutoLock);
+};
+
+// AutoUnlock is a helper that will Release() the |lock| argument in the
+// constructor, and re-Acquire() it in the destructor.
+class AutoUnlock {
+ public:
+ explicit AutoUnlock(Lock& lock) : lock_(lock) {
+ // We require our caller to have the lock.
+ lock_.AssertAcquired();
+ lock_.Release();
+ }
+
+ ~AutoUnlock() {
+ lock_.Acquire();
+ }
+
+ private:
+ Lock& lock_;
+ DISALLOW_COPY_AND_ASSIGN(AutoUnlock);
+};
+
+} // namespace base
+
+#endif // BASE_SYNCHRONIZATION_LOCK_H_