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 #pragma once 8 9 #include "base/base_api.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_API Lock { 19 public: 20 #if defined(NDEBUG) // Optimized wrapper implementation Lock()21 Lock() : lock_() {} ~Lock()22 ~Lock() {} Acquire()23 void Acquire() { lock_.Lock(); } Release()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). Try()30 bool Try() { return lock_.Try(); } 31 32 // Null implementation if not debug. AssertAcquired()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 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 // Windows doesn't need to do this as it calls the Lock::* methods. 66 friend class ConditionVariable; 67 #endif 68 69 private: 70 #if !defined(NDEBUG) 71 // Members and routines taking care of locks assertions. 72 // Note that this checks for recursive locks and allows them 73 // if the variable is set. This is allowed by the underlying implementation 74 // on windows but not on Posix, so we're doing unneeded checks on Posix. 75 // It's worth it to share the code. 76 void CheckHeldAndUnmark(); 77 void CheckUnheldAndMark(); 78 79 // All private data is implicitly protected by lock_. 80 // Be VERY careful to only access members under that lock. 81 82 // Determines validity of owning_thread_id_. Needed as we don't have 83 // a null owning_thread_id_ value. 84 bool owned_by_thread_; 85 base::PlatformThreadId owning_thread_id_; 86 #endif // NDEBUG 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: AutoLock(Lock & lock)97 explicit AutoLock(Lock& lock) : lock_(lock) { 98 lock_.Acquire(); 99 } 100 ~AutoLock()101 ~AutoLock() { 102 lock_.AssertAcquired(); 103 lock_.Release(); 104 } 105 106 private: 107 Lock& lock_; 108 DISALLOW_COPY_AND_ASSIGN(AutoLock); 109 }; 110 111 // AutoUnlock is a helper that will Release() the |lock| argument in the 112 // constructor, and re-Acquire() it in the destructor. 113 class AutoUnlock { 114 public: AutoUnlock(Lock & lock)115 explicit AutoUnlock(Lock& lock) : lock_(lock) { 116 // We require our caller to have the lock. 117 lock_.AssertAcquired(); 118 lock_.Release(); 119 } 120 ~AutoUnlock()121 ~AutoUnlock() { 122 lock_.Acquire(); 123 } 124 125 private: 126 Lock& lock_; 127 DISALLOW_COPY_AND_ASSIGN(AutoUnlock); 128 }; 129 130 } // namespace base 131 132 #endif // BASE_SYNCHRONIZATION_LOCK_H_ 133