Merge r181461 - Change WTF::ByteSpinLock to use std::atomic.

<https://webkit.org/b/142644> Reviewed by Filip Pizlo. * wtf/ByteSpinLock.h: (WTF::ByteSpinLock::ByteSpinLock): (WTF::ByteSpinLock::lock): (WTF::ByteSpinLock::unlock): (WTF::ByteSpinLock::isHeld):
WebKit · Mar 16, 2015 · 669f200 · 669f200
1 parent 30f7ca1
commit 669f200
Show file tree

Hide file tree

Showing 2 changed files with 22 additions and 8 deletions.
diff --git a/Source/WTF/ChangeLog b/Source/WTF/ChangeLog
@@ -1,3 +1,16 @@
+2015-03-12  Mark Lam  <mark.lam@apple.com>
+
+        Change WTF::ByteSpinLock to use std::atomic.
+        <https://webkit.org/b/142644>
+
+        Reviewed by Filip Pizlo.
+
+        * wtf/ByteSpinLock.h:
+        (WTF::ByteSpinLock::ByteSpinLock):
+        (WTF::ByteSpinLock::lock):
+        (WTF::ByteSpinLock::unlock):
+        (WTF::ByteSpinLock::isHeld):
+
 2015-03-12  Csaba Osztrogonác  <ossy@webkit.org>
 
         [ARM][Linux] GC sometimes stuck in an infinite loop if parallel GC is enabled

diff --git a/Source/WTF/wtf/ByteSpinLock.h b/Source/WTF/wtf/ByteSpinLock.h
@@ -26,9 +26,9 @@
 #ifndef ByteSpinLock_h
 #define ByteSpinLock_h
 
+#include <atomic>
 #include <thread>
 #include <wtf/Assertions.h>
-#include <wtf/Atomics.h>
 #include <wtf/Locker.h>
 #include <wtf/Noncopyable.h>
 
@@ -38,27 +38,28 @@ class ByteSpinLock {
     WTF_MAKE_NONCOPYABLE(ByteSpinLock);
 public:
     ByteSpinLock()
-        : m_lock(0)
+        : m_lock(false)
     {
     }
 
     void lock()
     {
-        while (!weakCompareAndSwap(&m_lock, 0, 1))
+        bool expected = false;
+        while (!m_lock.compare_exchange_weak(expected, true, std::memory_order_acquire)) {
             std::this_thread::yield();
-        memoryBarrierAfterLock();
+            expected = false;
+        }
     }
 
     void unlock()
     {
-        memoryBarrierBeforeUnlock();
-        m_lock = 0;
+        m_lock.store(false, std::memory_order_release);
     }
 
-    bool isHeld() const { return !!m_lock; }
+    bool isHeld() const { return m_lock.load(std::memory_order_acquire); }
 
 private:
-    uint8_t m_lock;
+    std::atomic<bool> m_lock;
 };
 
 typedef Locker<ByteSpinLock> ByteSpinLocker;