Index: base/synchronization/read_write_lock.h |
diff --git a/base/synchronization/read_write_lock.h b/base/synchronization/read_write_lock.h |
new file mode 100644 |
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+++ b/base/synchronization/read_write_lock.h |
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+// Copyright 2016 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_READ_WRITE_LOCK_H_ |
+#define BASE_SYNCHRONIZATION_READ_WRITE_LOCK_H_ |
+ |
+#include "base/base_export.h" |
+#include "base/macros.h" |
+#include "build/build_config.h" |
+ |
+#if defined(OS_NACL) |
+#include "base/synchronization/lock.h" |
+#endif |
+ |
+#if defined(OS_WIN) |
+#include <windows.h> |
+#elif defined(OS_POSIX) |
+#include <pthread.h> |
+#else |
+# error No reader-writer lock defined for this platform. |
+#endif |
+ |
+namespace base { |
+namespace subtle { |
+ |
+// An OS-independent wrapper around reader-writer locks. There's no magic here. |
+// |
+// You are strongly encouraged to use base::Lock instead of this, unless you |
+// can demonstrate contention and show that this would lead to an improvement. |
+// This lock does not make any guarantees of fairness, which can lead to writer |
+// starvation under certain access patterns. You should carefully consider your |
+// writer access patterns before using this lock. |
+class BASE_EXPORT ReadWriteLock { |
+ public: |
+ ReadWriteLock(); |
+ ~ReadWriteLock(); |
+ |
+ // Reader lock functions. |
+ void ReadAcquire(); |
+ void ReadRelease(); |
+ |
+ // Writer lock functions. |
+ void WriteAcquire(); |
+ void WriteRelease(); |
+ |
+ private: |
+#if defined(OS_WIN) |
+ using NativeHandle = SRWLOCK; |
+#elif defined(OS_NACL) |
+ using NativeHandle = Lock; |
+#elif defined(OS_POSIX) |
+ using NativeHandle = pthread_rwlock_t; |
+#endif |
+ |
+ NativeHandle native_handle_; |
+ |
+#if defined(OS_NACL) |
+ // Even though NaCl has a pthread_rwlock implementation, the build rules don't |
+ // make it universally available. So instead, implement a slower and trivial |
+ // reader-writer lock using a regular mutex. |
+ // TODO(amistry): Remove this and use the posix implementation when it's |
+ // available in all build configurations. |
+ uint32_t readers_ = 0; |
+ // base::Lock does checking to ensure the lock is acquired and released on the |
+ // same thread. This is not the case for this lock, so use pthread mutexes |
+ // directly here. |
+ pthread_mutex_t writer_lock_ = PTHREAD_MUTEX_INITIALIZER; |
+#endif |
+ |
+ DISALLOW_COPY_AND_ASSIGN(ReadWriteLock); |
+}; |
+ |
+class AutoReadLock { |
+ public: |
+ explicit AutoReadLock(ReadWriteLock& lock) : lock_(lock) { |
+ lock_.ReadAcquire(); |
+ } |
+ ~AutoReadLock() { |
+ lock_.ReadRelease(); |
+ } |
+ |
+ private: |
+ ReadWriteLock& lock_; |
+ DISALLOW_COPY_AND_ASSIGN(AutoReadLock); |
+}; |
+ |
+class AutoWriteLock { |
+ public: |
+ explicit AutoWriteLock(ReadWriteLock& lock) : lock_(lock) { |
+ lock_.WriteAcquire(); |
+ } |
+ ~AutoWriteLock() { |
+ lock_.WriteRelease(); |
+ } |
+ |
+ private: |
+ ReadWriteLock& lock_; |
+ DISALLOW_COPY_AND_ASSIGN(AutoWriteLock); |
+}; |
+ |
+} // namespace subtle |
+} // namespace base |
+ |
+#endif // BASE_SYNCHRONIZATION_READ_WRITE_LOCK_H_ |