Create a reader-writer lock implementaiton in base.

base/synchronization/read_write_lock_nacl.cc

Index: base/synchronization/read_write_lock_nacl.cc
diff --git a/base/synchronization/read_write_lock_nacl.cc b/base/synchronization/read_write_lock_nacl.cc
new file mode 100644
index 0000000000000000000000000000000000000000..7278b1f52cdee3f7b9a8a7d1666923f8c214409f
--- /dev/null
+++ b/base/synchronization/read_write_lock_nacl.cc
@@ -0,0 +1,49 @@
+// 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.
+
+#include "base/synchronization/read_write_lock.h"
+
+#include "base/logging.h"
+
+namespace base {
+namespace subtle {
+
+ReadWriteLock::ReadWriteLock() {}
+
+ReadWriteLock::~ReadWriteLock() {
+  DCHECK_EQ(0u, readers_);
+  int result = pthread_mutex_destroy(&writer_lock_);
+  DCHECK_EQ(result, 0) << ". " << strerror(result);
+}
+
+void ReadWriteLock::ReadAcquire() {
+  AutoLock hold(native_handle_);
+  readers_++;
+  if (readers_ == 1) {
+    int result = pthread_mutex_lock(&writer_lock_);
+    DCHECK_EQ(result, 0) << ". " << strerror(result);
+  }
+}
+
+void ReadWriteLock::ReadRelease() {
+  AutoLock hold(native_handle_);
+  readers_--;
+  if (readers_ == 0) {
+    int result = pthread_mutex_unlock(&writer_lock_);
+    DCHECK_EQ(result, 0) << ". " << strerror(result);
+  }
+}
+
+void ReadWriteLock::WriteAcquire() {
+  int result = pthread_mutex_lock(&writer_lock_);
+  DCHECK_EQ(result, 0) << ". " << strerror(result);
+}
+
+void ReadWriteLock::WriteRelease() {
+  int result = pthread_mutex_unlock(&writer_lock_);
+  DCHECK_EQ(result, 0) << ". " << strerror(result);
+}
+
+}  // namespace subtle
+}  // namespace base