base/synchronization/lock.h

   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/logging.h"
  10 #include "base/synchronization/lock_impl.h"
  11 #include "base/threading/platform_thread.h"
  12
  13 namespace base {
  14
  15 // A convenient wrapper for an OS specific critical section.  The only real
  16 // intelligence in this class is in debug mode for the support for the
  17 // AssertAcquired() method.
  18 class BASE_EXPORT Lock {
  19  public:
  20 #if !DCHECK_IS_ON()
  21    // Optimized wrapper implementation
  22   Lock() : lock_() {}
  23   ~Lock() {}
  24   void Acquire() { lock_.Lock(); }
  25   void Release() { lock_.Unlock(); }
  26
  27   // If the lock is not held, take it and return true. If the lock is already
  28   // held by another thread, immediately return false. This must not be called
  29   // by a thread already holding the lock (what happens is undefined and an
  30   // assertion may fail).
  31   bool Try() { return lock_.Try(); }
  32
  33   // Null implementation if not debug.
  34   void AssertAcquired() const {}
  35 #else
  36   Lock();
  37   ~Lock();
  38
  39   // NOTE: Although windows critical sections support recursive locks, we do not
  40   // allow this, and we will commonly fire a DCHECK() if a thread attempts to
  41   // acquire the lock a second time (while already holding it).
  42   void Acquire() {
  43     lock_.Lock();
  44     CheckUnheldAndMark();
  45   }
  46   void Release() {
  47     CheckHeldAndUnmark();
  48     lock_.Unlock();
  49   }
  50
  51   bool Try() {
  52     bool rv = lock_.Try();
  53     if (rv) {
  54       CheckUnheldAndMark();
  55     }
  56     return rv;
  57   }
  58
  59   void AssertAcquired() const;
  60 #endif  // DCHECK_IS_ON()
  61
  62 #if defined(OS_POSIX)
  63   // The posix implementation of ConditionVariable needs to be able
  64   // to see our lock and tweak our debugging counters, as it releases
  65   // and acquires locks inside of pthread_cond_{timed,}wait.
  66   friend class ConditionVariable;
  67 #elif defined(OS_WIN)
  68   // The Windows Vista implementation of ConditionVariable needs the
  69   // native handle of the critical section.
  70   friend class WinVistaCondVar;
  71 #endif
  72
  73  private:
  74 #if DCHECK_IS_ON()
  75   // Members and routines taking care of locks assertions.
  76   // Note that this checks for recursive locks and allows them
  77   // if the variable is set.  This is allowed by the underlying implementation
  78   // on windows but not on Posix, so we're doing unneeded checks on Posix.
  79   // It's worth it to share the code.
  80   void CheckHeldAndUnmark();
  81   void CheckUnheldAndMark();
  82
  83   // All private data is implicitly protected by lock_.
  84   // Be VERY careful to only access members under that lock.
  85   base::PlatformThreadRef owning_thread_ref_;
  86 #endif  // DCHECK_IS_ON()
  87
  88   // Platform specific underlying lock implementation.
  89   internal::LockImpl lock_;
  90
  91   DISALLOW_COPY_AND_ASSIGN(Lock);
  92 };
  93
  94 // A helper class that acquires the given Lock while the AutoLock is in scope.
  95 class AutoLock {
  96  public:
  97   struct AlreadyAcquired {};
  98
  99   explicit AutoLock(Lock& lock) : lock_(lock) {
 100     lock_.Acquire();
 101   }
 102
 103   AutoLock(Lock& lock, const AlreadyAcquired&) : lock_(lock) {
 104     lock_.AssertAcquired();
 105   }
 106
 107   ~AutoLock() {
 108     lock_.AssertAcquired();
 109     lock_.Release();
 110   }
 111
 112  private:
 113   Lock& lock_;
 114   DISALLOW_COPY_AND_ASSIGN(AutoLock);
 115 };
 116
 117 // AutoUnlock is a helper that will Release() the |lock| argument in the
 118 // constructor, and re-Acquire() it in the destructor.
 119 class AutoUnlock {
 120  public:
 121   explicit AutoUnlock(Lock& lock) : lock_(lock) {
 122     // We require our caller to have the lock.
 123     lock_.AssertAcquired();
 124     lock_.Release();
 125   }
 126
 127   ~AutoUnlock() {
 128     lock_.Acquire();
 129   }
 130
 131  private:
 132   Lock& lock_;
 133   DISALLOW_COPY_AND_ASSIGN(AutoUnlock);
 134 };
 135
 136 }  // namespace base
 137
 138 #endif  // BASE_SYNCHRONIZATION_LOCK_H_