Move WTF::SpinLock to base::SpinLock.

base/spin_lock.h

 /*

[kinuko, 2016/11/08 05:15:42]

drive-by.  Should these files be maybe put under base/synchronization ?

Also could we use short copyright format?

  * 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.
  */
 
-#ifndef WTF_SpinLock_h
-#define WTF_SpinLock_h
+#ifndef BASE_OPTIONAL_H
+#define BASE_OPTIONAL_H
 
-#include "wtf/Compiler.h"
-#include "wtf/WTFExport.h"
 #include <atomic>
 #include <memory>
 #include <mutex>
 
-// DESCRIPTION
+#include "base/base_export.h"
+#include "base/compiler_specific.h"
+
 // 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.
 
-namespace WTF {
+namespace base {
 
 class SpinLock {
  public:
   using Guard = std::lock_guard<SpinLock>;
 
+  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)))
+    static_assert(sizeof(lock_) == sizeof(int),
+                  "int and lock_ are different sizes");
+    if (LIKELY(!lock_.exchange(true, std::memory_order_acquire)))
       return;
-    lockSlow();
+    LockSlow();
   }
 
-  ALWAYS_INLINE void unlock() {
-    m_lock.store(false, std::memory_order_release);
-  }
+  ALWAYS_INLINE void unlock() { 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();
+  BASE_EXPORT void LockSlow();
 
-  std::atomic_int m_lock;
+  std::atomic_int lock_;
 };
 
-}  // namespace WTF
+}  // namespace base
 
-using WTF::SpinLock;
-
-#endif  // WTF_SpinLock_h
+#endif  // BASE_OPTIONAL_H