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.
4
5#ifndef BASE_SYNCHRONIZATION_LOCK_H_
6#define BASE_SYNCHRONIZATION_LOCK_H_
7
8#include "base/base_export.h"
9#include "base/synchronization/lock_impl.h"
10#include "base/threading/platform_thread.h"
11
12namespace base {
13
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.
17class BASE_EXPORT Lock {
18 public:
19#if defined(NDEBUG) && !defined(DCHECK_ALWAYS_ON)
20   // Optimized wrapper implementation
21  Lock() : lock_() {}
22  ~Lock() {}
23  void Acquire() { lock_.Lock(); }
24  void Release() { lock_.Unlock(); }
25
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(); }
31
32  // Null implementation if not debug.
33  void AssertAcquired() const {}
34#else
35  Lock();
36  ~Lock();
37
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).
41  void Acquire() {
42    lock_.Lock();
43    CheckUnheldAndMark();
44  }
45  void Release() {
46    CheckHeldAndUnmark();
47    lock_.Unlock();
48  }
49
50  bool Try() {
51    bool rv = lock_.Try();
52    if (rv) {
53      CheckUnheldAndMark();
54    }
55    return rv;
56  }
57
58  void AssertAcquired() const;
59#endif  // NDEBUG && !DCHECK_ALWAYS_ON
60
61#if defined(OS_POSIX)
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;
66#elif defined(OS_WIN)
67  // The Windows Vista implementation of ConditionVariable needs the
68  // native handle of the critical section.
69  friend class WinVistaCondVar;
70#endif
71
72 private:
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();
81
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
86
87  // Platform specific underlying lock implementation.
88  internal::LockImpl lock_;
89
90  DISALLOW_COPY_AND_ASSIGN(Lock);
91};
92
93// A helper class that acquires the given Lock while the AutoLock is in scope.
94class AutoLock {
95 public:
96  struct AlreadyAcquired {};
97
98  explicit AutoLock(Lock& lock) : lock_(lock) {
99    lock_.Acquire();
100  }
101
102  AutoLock(Lock& lock, const AlreadyAcquired&) : lock_(lock) {
103    lock_.AssertAcquired();
104  }
105
106  ~AutoLock() {
107    lock_.AssertAcquired();
108    lock_.Release();
109  }
110
111 private:
112  Lock& lock_;
113  DISALLOW_COPY_AND_ASSIGN(AutoLock);
114};
115
116// AutoUnlock is a helper that will Release() the |lock| argument in the
117// constructor, and re-Acquire() it in the destructor.
118class AutoUnlock {
119 public:
120  explicit AutoUnlock(Lock& lock) : lock_(lock) {
121    // We require our caller to have the lock.
122    lock_.AssertAcquired();
123    lock_.Release();
124  }
125
126  ~AutoUnlock() {
127    lock_.Acquire();
128  }
129
130 private:
131  Lock& lock_;
132  DISALLOW_COPY_AND_ASSIGN(AutoUnlock);
133};
134
135}  // namespace base
136
137#endif  // BASE_SYNCHRONIZATION_LOCK_H_
138