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