CL for perf tryjob ThreadSafeRefCountedStringImpl Linux blink_perf.dom

Source/wtf/text/StringImpl.h

Index: Source/wtf/text/StringImpl.h
diff --git a/Source/wtf/text/StringImpl.h b/Source/wtf/text/StringImpl.h
index 4c5fb01607778ad77ea6c7e7dec8cba0de257cd2..1682171712bf672c9520d02193ebcdee0ec5c3eb 100644
--- a/Source/wtf/text/StringImpl.h
+++ b/Source/wtf/text/StringImpl.h
@@ -25,6 +25,7 @@
 
 #include <limits.h>
 #include "wtf/ASCIICType.h"
+#include "wtf/DynamicAnnotations.h"
 #include "wtf/Forward.h"
 #include "wtf/HashMap.h"
 #include "wtf/StringHasher.h"
@@ -283,24 +284,28 @@ public:
         return hashSlowCase();
     }
 
+    ALWAYS_INLINE unsigned refCount() const
+    {
+        return static_cast<int const volatile &>(m_refCount);
+    }
+
     ALWAYS_INLINE bool hasOneRef() const
     {
-        return m_refCount == 1;
+        return refCount() == 1;
     }
 
     ALWAYS_INLINE void ref()
     {
-        ++m_refCount;
+        atomicIncrement(&m_refCount);
     }
 
     ALWAYS_INLINE void deref()
     {
-        if (hasOneRef()) {
+        WTF_ANNOTATE_HAPPENS_BEFORE(&m_refCount);
+        if (atomicDecrement(&m_refCount) <= 0) {
+            WTF_ANNOTATE_HAPPENS_AFTER(&m_refCount);

[Alexander Potapenko, 2014/12/08 11:46:57]

Please do not use WTF_ANNOTATE_HAPPENS_AFTER.
They were intended to aid TSan v1, which couldn't comprehend atomics, and which
is retired now.
TSan v2 is able to understand atomic-based synchronization, and adding excessive
happens-before annotations may mask actual errors in the implementation.
I think we should plan removing all WTF_ANNOTATE_HAPPENS_{BEFORE,AFTER} from
Blink at some point.

             destroyIfNotStatic();
-            return;
         }
-
-        --m_refCount;
     }
 
     static StringImpl* empty();
@@ -448,7 +453,7 @@ private:
 #endif
 
 private:
-    unsigned m_refCount;
+    int m_refCount;
     unsigned m_length;
     mutable unsigned m_hash : 24;
     unsigned m_isAtomic : 1;