Move WTF::SpinLock to base::SpinLock.

third_party/WebKit/Source/wtf/SpinLock.h

-/*
- * Copyright (C) 2013 Google Inc. All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions are
- * met:
- *
- *     * Redistributions of source code must retain the above copyright
- * notice, this list of conditions and the following disclaimer.
- *     * Redistributions in binary form must reproduce the above
- * copyright notice, this list of conditions and the following disclaimer
- * in the documentation and/or other materials provided with the
- * distribution.
- *     * Neither the name of Google Inc. nor the names of its
- * contributors may be used to endorse or promote products derived from
- * this software without specific prior written permission.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
- * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
- * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
- * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
- * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
- * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
- * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
- * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
- * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
- */
+// 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 WTF_SpinLock_h
 #define WTF_SpinLock_h
 
-#include "wtf/Compiler.h"
-#include "wtf/WTFExport.h"
-#include <atomic>
-#include <memory>
-#include <mutex>
-
-// DESCRIPTION
-// Spinlock is a simple spinlock class based on the standard CPU primitive of
-// atomic increment and decrement of an int at a given memory address. These are
-// intended only for very short duration locks and assume a system with multiple
-// cores. For any potentially longer wait you should be using a real lock.
+#include "base/macros.h"
+#include "base/synchronization/spin_lock.h"
 
 namespace WTF {
 
-class SpinLock {
- public:
-  using Guard = std::lock_guard<SpinLock>;
-
-  ALWAYS_INLINE void lock() {
-    static_assert(sizeof(m_lock) == sizeof(int),
-                  "int and m_lock are different sizes");
-    if (LIKELY(!m_lock.exchange(true, std::memory_order_acquire)))
-      return;
-    lockSlow();
-  }
-
-  ALWAYS_INLINE void unlock() {
-    m_lock.store(false, std::memory_order_release);
-  }
-
- private:
-  // This is called if the initial attempt to acquire the lock fails. It's
-  // slower, but has a much better scheduling and power consumption behavior.
-  WTF_EXPORT void lockSlow();
-
-  std::atomic_int m_lock;
-};
+// WTF::SpinLock is base::SpinLock. See base/synchronization/spin_lock.h for
+// documentation.
+using SpinLock = base::subtle::SpinLock;
 
 }  // namespace WTF
 
 using WTF::SpinLock;
 
 #endif  // WTF_SpinLock_h