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/thread_annotations.h" 13 #include "base/threading/platform_thread.h" 14 #include "build/build_config.h" 15 16 namespace base { 17 18 // A convenient wrapper for an OS specific critical section. The only real 19 // intelligence in this class is in debug mode for the support for the 20 // AssertAcquired() method. 21 class LOCKABLE BASE_EXPORT Lock { 22 public: 23 #if !DCHECK_IS_ON() 24 // Optimized wrapper implementation Lock()25 Lock() : lock_() {} ~Lock()26 ~Lock() {} 27 Acquire()28 void Acquire() EXCLUSIVE_LOCK_FUNCTION() { lock_.Lock(); } Release()29 void Release() UNLOCK_FUNCTION() { lock_.Unlock(); } 30 31 // If the lock is not held, take it and return true. If the lock is already 32 // held by another thread, immediately return false. This must not be called 33 // by a thread already holding the lock (what happens is undefined and an 34 // assertion may fail). Try()35 bool Try() EXCLUSIVE_TRYLOCK_FUNCTION(true) { return lock_.Try(); } 36 37 // Null implementation if not debug. AssertAcquired()38 void AssertAcquired() const ASSERT_EXCLUSIVE_LOCK() {} 39 #else 40 Lock(); 41 ~Lock(); 42 43 // NOTE: We do not permit recursive locks and will commonly fire a DCHECK() if 44 // a thread attempts to acquire the lock a second time (while already holding 45 // it). 46 void Acquire() EXCLUSIVE_LOCK_FUNCTION() { 47 lock_.Lock(); 48 CheckUnheldAndMark(); 49 } 50 void Release() UNLOCK_FUNCTION() { 51 CheckHeldAndUnmark(); 52 lock_.Unlock(); 53 } 54 55 bool Try() EXCLUSIVE_TRYLOCK_FUNCTION(true) { 56 bool rv = lock_.Try(); 57 if (rv) { 58 CheckUnheldAndMark(); 59 } 60 return rv; 61 } 62 63 void AssertAcquired() const ASSERT_EXCLUSIVE_LOCK(); 64 #endif // DCHECK_IS_ON() 65 66 // Whether Lock mitigates priority inversion when used from different thread 67 // priorities. HandlesMultipleThreadPriorities()68 static bool HandlesMultipleThreadPriorities() { 69 #if defined(OS_WIN) 70 // Windows mitigates priority inversion by randomly boosting the priority of 71 // ready threads. 72 // https://msdn.microsoft.com/library/windows/desktop/ms684831.aspx 73 return true; 74 #elif defined(OS_POSIX) || defined(OS_FUCHSIA) 75 // POSIX mitigates priority inversion by setting the priority of a thread 76 // holding a Lock to the maximum priority of any other thread waiting on it. 77 return internal::LockImpl::PriorityInheritanceAvailable(); 78 #else 79 #error Unsupported platform 80 #endif 81 } 82 83 // Both Windows and POSIX implementations of ConditionVariable need to be 84 // able to see our lock and tweak our debugging counters, as they release and 85 // acquire locks inside of their condition variable APIs. 86 friend class ConditionVariable; 87 88 private: 89 #if DCHECK_IS_ON() 90 // Members and routines taking care of locks assertions. 91 // Note that this checks for recursive locks and allows them 92 // if the variable is set. This is allowed by the underlying implementation 93 // on windows but not on Posix, so we're doing unneeded checks on Posix. 94 // It's worth it to share the code. 95 void CheckHeldAndUnmark(); 96 void CheckUnheldAndMark(); 97 98 // All private data is implicitly protected by lock_. 99 // Be VERY careful to only access members under that lock. 100 base::PlatformThreadRef owning_thread_ref_; 101 #endif // DCHECK_IS_ON() 102 103 // Platform specific underlying lock implementation. 104 internal::LockImpl lock_; 105 106 DISALLOW_COPY_AND_ASSIGN(Lock); 107 }; 108 109 // A helper class that acquires the given Lock while the AutoLock is in scope. 110 using AutoLock = internal::BasicAutoLock<Lock>; 111 112 // AutoUnlock is a helper that will Release() the |lock| argument in the 113 // constructor, and re-Acquire() it in the destructor. 114 using AutoUnlock = internal::BasicAutoUnlock<Lock>; 115 116 // Like AutoLock but is a no-op when the provided Lock* is null. Inspired from 117 // absl::MutexLockMaybe. Use this instead of base::Optional<base::AutoLock> to 118 // get around -Wthread-safety-analysis warnings for conditional locking. 119 using AutoLockMaybe = internal::BasicAutoLockMaybe<Lock>; 120 121 // Like AutoLock but permits Release() of its mutex before destruction. 122 // Release() may be called at most once. Inspired from 123 // absl::ReleasableMutexLock. Use this instead of base::Optional<base::AutoLock> 124 // to get around -Wthread-safety-analysis warnings for AutoLocks that are 125 // explicitly released early (prefer proper scoping to this). 126 using ReleasableAutoLock = internal::BasicReleasableAutoLock<Lock>; 127 128 } // namespace base 129 130 #endif // BASE_SYNCHRONIZATION_LOCK_H_ 131