Switch wtf/SpinLock to std::atomic

third_party/WebKit/Source/wtf/SpinLock.h

Index: third_party/WebKit/Source/wtf/SpinLock.h
diff --git a/third_party/WebKit/Source/wtf/SpinLock.h b/third_party/WebKit/Source/wtf/SpinLock.h
index 08724a370abb4bb6e4d861dfa267c3ea7ab89f91..b8d6b9c65ed1188e8abae37f2fed0e69d833bf8f 100644
--- a/third_party/WebKit/Source/wtf/SpinLock.h
+++ b/third_party/WebKit/Source/wtf/SpinLock.h
@@ -31,36 +31,48 @@
 #ifndef WTF_SpinLock_h
 #define WTF_SpinLock_h
 
-// 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/Compiler.h"
+#include "wtf/WTFExport.h"
+#include <atomic>
+#include <memory>
+#include <mutex>
 
-#include "wtf/Atomics.h"
+// 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.
 
 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 lock()
+    {
+        static_assert(sizeof(m_lock) == sizeof(int), "int and m_lock are different sizes");
+        if (LIKELY(!m_lock.exchange(true, std::memory_order_acq_rel)))
+            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();
 
-ALWAYS_INLINE void spinLockLock(int volatile* lock)
-{
-    if (LIKELY(!atomicTestAndSetToOne(lock)))
-        return;
-    slowSpinLockLock(lock);
-}
+    std::atomic<int> m_lock;
+};
 
-ALWAYS_INLINE void spinLockUnlock(int volatile* lock)
-{
-    atomicSetOneToZero(lock);
-}
 
 } // namespace WTF
 
-using WTF::spinLockLock;
-using WTF::spinLockUnlock;
+using WTF::SpinLock;
 
 #endif // WTF_SpinLock_h