Make |Heap::findGCInfo()| threadsafe.

Source/platform/heap/Heap.cpp

Index: Source/platform/heap/Heap.cpp
diff --git a/Source/platform/heap/Heap.cpp b/Source/platform/heap/Heap.cpp
index f055df916d27a153d4ccc00a1fa90cbafe0dbb5b..b7c72bfaf0ec1c37d67f278b500a0809b3e3d194 100644
--- a/Source/platform/heap/Heap.cpp
+++ b/Source/platform/heap/Heap.cpp
@@ -1600,12 +1600,20 @@ Address Heap::checkAndMarkPointer(Visitor* visitor, Address address)
 #if ENABLE(GC_TRACING)
 const GCInfo* Heap::findGCInfo(Address address)
 {
+    bool needLockForIteration = !ThreadState::current()->isAtSafePoint();

[haraken, 2014/06/05 09:11:23]

I guess what matters is not whether we're at a safe point but whether we're in a
GC. If so, we should check ThreadState::isAnyThreadInGC() instead of
isAtSafePoint().

[kouhei (in TOK), 2014/06/05 09:26:22]

Done.

+    if (needLockForIteration)
+        ThreadState::threadAttachMutex().lock();
+
     ThreadState::AttachedThreadStateSet& threads = ThreadState::attachedThreads();
     for (ThreadState::AttachedThreadStateSet::iterator it = threads.begin(), end = threads.end(); it != end; ++it) {
         if (const GCInfo* gcInfo = (*it)->findGCInfo(address)) {
+            if (needLockForIteration)
+                ThreadState::threadAttachMutex().unlock();
             return gcInfo;
         }
     }
+    if (needLockForIteration)
+        ThreadState::threadAttachMutex().unlock();
     return 0;
 }