Switch wtf/SpinLock to std::atomic

third_party/WebKit/Source/wtf/SpinLock.cpp

 // Copyright 2015 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.
 
 #include "config.h"
 #include "wtf/SpinLock.h"
 
 #include "wtf/Atomics.h"
 #include "wtf/CPU.h"
 #include "wtf/Compiler.h"
@@ skipping 35 matching lines @@
 #if OS(POSIX)
 #define YIELD_THREAD sched_yield()
 #else
 #warning "Thread yield not supported on this OS."
 #define YIELD_THREAD ((void)0)
 #endif
 #endif
 
 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.
     // TODO(jschuh): Further tuning may be warranted.
     static const int kYieldProcessorTries = 1000;
     do {
         do {
             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