1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
5 #ifndef BASE_SYNCHRONIZATION_LOCK_H_
6 #define BASE_SYNCHRONIZATION_LOCK_H_
8 #include "base/base_export.h"
9 #include "base/synchronization/lock_impl.h"
10 #include "base/threading/platform_thread.h"
14 // A convenient wrapper for an OS specific critical section. The only real
15 // intelligence in this class is in debug mode for the support for the
16 // AssertAcquired() method.
17 class BASE_EXPORT Lock {
19 #if defined(NDEBUG) && !defined(DCHECK_ALWAYS_ON)
20 // Optimized wrapper implementation
23 void Acquire() { lock_.Lock(); }
24 void Release() { lock_.Unlock(); }
26 // If the lock is not held, take it and return true. If the lock is already
27 // held by another thread, immediately return false. This must not be called
28 // by a thread already holding the lock (what happens is undefined and an
29 // assertion may fail).
30 bool Try() { return lock_.Try(); }
32 // Null implementation if not debug.
33 void AssertAcquired() const {}
38 // NOTE: Although windows critical sections support recursive locks, we do not
39 // allow this, and we will commonly fire a DCHECK() if a thread attempts to
40 // acquire the lock a second time (while already holding it).
51 bool rv = lock_.Try();
58 void AssertAcquired() const;
59 #endif // NDEBUG && !DCHECK_ALWAYS_ON
62 // The posix implementation of ConditionVariable needs to be able
63 // to see our lock and tweak our debugging counters, as it releases
64 // and acquires locks inside of pthread_cond_{timed,}wait.
65 friend class ConditionVariable;
67 // The Windows Vista implementation of ConditionVariable needs the
68 // native handle of the critical section.
69 friend class WinVistaCondVar;
73 #if !defined(NDEBUG) || defined(DCHECK_ALWAYS_ON)
74 // Members and routines taking care of locks assertions.
75 // Note that this checks for recursive locks and allows them
76 // if the variable is set. This is allowed by the underlying implementation
77 // on windows but not on Posix, so we're doing unneeded checks on Posix.
78 // It's worth it to share the code.
79 void CheckHeldAndUnmark();
80 void CheckUnheldAndMark();
82 // All private data is implicitly protected by lock_.
83 // Be VERY careful to only access members under that lock.
84 base::PlatformThreadRef owning_thread_ref_;
85 #endif // !NDEBUG || DCHECK_ALWAYS_ON
87 // Platform specific underlying lock implementation.
88 internal::LockImpl lock_;
90 DISALLOW_COPY_AND_ASSIGN(Lock);
93 // A helper class that acquires the given Lock while the AutoLock is in scope.
96 struct AlreadyAcquired {};
98 explicit AutoLock(Lock& lock) : lock_(lock) {
102 AutoLock(Lock& lock, const AlreadyAcquired&) : lock_(lock) {
103 lock_.AssertAcquired();
107 lock_.AssertAcquired();
113 DISALLOW_COPY_AND_ASSIGN(AutoLock);
116 // AutoUnlock is a helper that will Release() the |lock| argument in the
117 // constructor, and re-Acquire() it in the destructor.
120 explicit AutoUnlock(Lock& lock) : lock_(lock) {
121 // We require our caller to have the lock.
122 lock_.AssertAcquired();
132 DISALLOW_COPY_AND_ASSIGN(AutoUnlock);
137 #endif // BASE_SYNCHRONIZATION_LOCK_H_