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