Switch wtf/SpinLock to std::atomic

third_party/WebKit/Source/wtf/SpinLock.cpp

Index: third_party/WebKit/Source/wtf/SpinLock.cpp
diff --git a/third_party/WebKit/Source/wtf/SpinLock.cpp b/third_party/WebKit/Source/wtf/SpinLock.cpp
index 542f97be672d9daa58242adadf775ff4bf0491a8..5971c50a566e0554c3902084009c3884c0fe4ea1 100644
--- a/third_party/WebKit/Source/wtf/SpinLock.cpp
+++ b/third_party/WebKit/Source/wtf/SpinLock.cpp
@@ -53,7 +53,7 @@
 
 namespace WTF {
 
-void slowSpinLockLock(int volatile* lock)
+void SpinLock::SlowLock()
 {
     // The value of kYieldProcessorTries is cargo culted from TCMalloc, Windows
     // critical section defaults, and various other recommendations.
@@ -64,14 +64,14 @@ void slowSpinLockLock(int volatile* lock)
             for (int count = 0; count < kYieldProcessorTries; ++count) {
                 // Let the Processor know we're spinning.
                 YIELD_PROCESSOR;
-                if (!*lock && LIKELY(!atomicTestAndSetToOne(lock)))
+                if (!m_lock.load() && LIKELY(!m_lock.exchange(true)))

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

load() can be made memory_order_relaxed, and exchange() - memory_order_acq_rel.

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

Done.

                     return;
             }
 
             // Give the OS a chance to schedule something on this core.
             YIELD_THREAD;
-        } while (*lock);
-    } while (UNLIKELY(atomicTestAndSetToOne(lock)));
+        } while (m_lock.exchange(true));

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

memory_order_acq_rel

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

Actually, this was a mistake on my part and should just be a load with
memory_order_relaxed.

+    } while (UNLIKELY(m_lock.exchange(true)));

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

ditto.

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

Done.

 }
 
 } // namespace WTF