Repo created

TMessagesProj/jni/voip/webrtc/base/synchronization/lock.h

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+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_SYNCHRONIZATION_LOCK_H_
+#define BASE_SYNCHRONIZATION_LOCK_H_
+
+#include "base/base_export.h"
+#include "base/logging.h"
+#include "base/macros.h"
+#include "base/synchronization/lock_impl.h"
+#include "base/thread_annotations.h"
+#include "base/threading/platform_thread.h"
+#include "build/build_config.h"
+
+namespace base {
+
+// A convenient wrapper for an OS specific critical section.  The only real
+// intelligence in this class is in debug mode for the support for the
+// AssertAcquired() method.
+class LOCKABLE BASE_EXPORT Lock {
+ public:
+#if !DCHECK_IS_ON()
+  // Optimized wrapper implementation
+  Lock() : lock_() {}
+  ~Lock() {}
+
+  void Acquire() EXCLUSIVE_LOCK_FUNCTION() { lock_.Lock(); }
+  void Release() UNLOCK_FUNCTION() { lock_.Unlock(); }
+
+  // If the lock is not held, take it and return true. If the lock is already
+  // held by another thread, immediately return false. This must not be called
+  // by a thread already holding the lock (what happens is undefined and an
+  // assertion may fail).
+  bool Try() EXCLUSIVE_TRYLOCK_FUNCTION(true) { return lock_.Try(); }
+
+  // Null implementation if not debug.
+  void AssertAcquired() const ASSERT_EXCLUSIVE_LOCK() {}
+#else
+  Lock();
+  ~Lock();
+
+  // NOTE: We do not permit recursive locks and will commonly fire a DCHECK() if
+  // a thread attempts to acquire the lock a second time (while already holding
+  // it).
+  void Acquire() EXCLUSIVE_LOCK_FUNCTION() {
+    lock_.Lock();
+    CheckUnheldAndMark();
+  }
+  void Release() UNLOCK_FUNCTION() {
+    CheckHeldAndUnmark();
+    lock_.Unlock();
+  }
+
+  bool Try() EXCLUSIVE_TRYLOCK_FUNCTION(true) {
+    bool rv = lock_.Try();
+    if (rv) {
+      CheckUnheldAndMark();
+    }
+    return rv;
+  }
+
+  void AssertAcquired() const ASSERT_EXCLUSIVE_LOCK();
+#endif  // DCHECK_IS_ON()
+
+  // Whether Lock mitigates priority inversion when used from different thread
+  // priorities.
+  static bool HandlesMultipleThreadPriorities() {
+#if defined(OS_WIN)
+    // Windows mitigates priority inversion by randomly boosting the priority of
+    // ready threads.
+    // https://msdn.microsoft.com/library/windows/desktop/ms684831.aspx
+    return true;
+#elif defined(OS_POSIX) || defined(OS_FUCHSIA)
+    // POSIX mitigates priority inversion by setting the priority of a thread
+    // holding a Lock to the maximum priority of any other thread waiting on it.
+    return internal::LockImpl::PriorityInheritanceAvailable();
+#else
+#error Unsupported platform
+#endif
+  }
+
+  // Both Windows and POSIX implementations of ConditionVariable need to be
+  // able to see our lock and tweak our debugging counters, as they release and
+  // acquire locks inside of their condition variable APIs.
+  friend class ConditionVariable;
+
+ private:
+#if DCHECK_IS_ON()
+  // Members and routines taking care of locks assertions.
+  // Note that this checks for recursive locks and allows them
+  // if the variable is set.  This is allowed by the underlying implementation
+  // on windows but not on Posix, so we're doing unneeded checks on Posix.
+  // It's worth it to share the code.
+  void CheckHeldAndUnmark();
+  void CheckUnheldAndMark();
+
+  // All private data is implicitly protected by lock_.
+  // Be VERY careful to only access members under that lock.
+  base::PlatformThreadRef owning_thread_ref_;
+#endif  // DCHECK_IS_ON()
+
+  // Platform specific underlying lock implementation.
+  internal::LockImpl lock_;
+
+  DISALLOW_COPY_AND_ASSIGN(Lock);
+};
+
+// A helper class that acquires the given Lock while the AutoLock is in scope.
+using AutoLock = internal::BasicAutoLock<Lock>;
+
+// AutoUnlock is a helper that will Release() the |lock| argument in the
+// constructor, and re-Acquire() it in the destructor.
+using AutoUnlock = internal::BasicAutoUnlock<Lock>;
+
+// Like AutoLock but is a no-op when the provided Lock* is null. Inspired from
+// absl::MutexLockMaybe. Use this instead of base::Optional<base::AutoLock> to
+// get around -Wthread-safety-analysis warnings for conditional locking.
+using AutoLockMaybe = internal::BasicAutoLockMaybe<Lock>;
+
+// Like AutoLock but permits Release() of its mutex before destruction.
+// Release() may be called at most once. Inspired from
+// absl::ReleasableMutexLock. Use this instead of base::Optional<base::AutoLock>
+// to get around -Wthread-safety-analysis warnings for AutoLocks that are
+// explicitly released early (prefer proper scoping to this).
+using ReleasableAutoLock = internal::BasicReleasableAutoLock<Lock>;
+
+}  // namespace base
+
+#endif  // BASE_SYNCHRONIZATION_LOCK_H_