Switch wtf/SpinLock to std::atomic

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
@@ skipping 13 matching lines @@
  * 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
 
+#include "wtf/Compiler.h"
+#include "wtf/WTFExport.h"
+#include <atomic>
+#include <memory>
+#include <mutex>
+
 // DESCRIPTION
-// spinLockLock() and spinLockUnlock() are simple spinlock primitives 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 "wtf/Atomics.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 {
 
-// This is called if the initial attempt to acquire the lock fails. It's a bit
-// slower, but has a much better scheduling and power consumption behavior.
-WTF_EXPORT void slowSpinLockLock(int volatile* lock);
+class SpinLock {
+public:
+    using Guard = std::lock_guard<SpinLock>;
 
-ALWAYS_INLINE void spinLockLock(int volatile* lock)
-{
-    if (LIKELY(!atomicTestAndSetToOne(lock)))
-        return;
-    slowSpinLockLock(lock);
-}
+    ALWAYS_INLINE void lock()
+    {
+        static_assert(sizeof(m_lock) == sizeof(int), "int and m_lock are different sizes");
+        if (LIKELY(!m_lock.exchange(true)))

[Alexander Potapenko, 2015/12/04 12:17:34]

I suppose it's enough to have memory_order_acq_rel here.

[jschuh, 2015/12/04 20:45:13]

Done.

+            return;
+        SlowLock();
+    }
 
-ALWAYS_INLINE void spinLockUnlock(int volatile* lock)
-{
-    atomicSetOneToZero(lock);
-}
+    ALWAYS_INLINE void unlock()
+    {
+        m_lock.store(false);

[Alexander Potapenko, 2015/12/04 12:17:34]

Should be enough to store with memory_order_release.

[jschuh, 2015/12/04 20:45:13]

Done.

+    }
+
+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 SlowLock();

[Yuta Kitamura, 2015/12/04 03:36:28]

Follow Blink's naming convention.

[jschuh, 2015/12/04 20:45:13]

Done.

+
+    std::atomic<int> m_lock;
+};
+
 
 } // namespace WTF
 
-using WTF::spinLockLock;
-using WTF::spinLockUnlock;
+using WTF::SpinLock;
 
 #endif // WTF_SpinLock_h