diff -r 000000000000 -r 4f2f89ce4247 JavaScriptCore/runtime/WeakGCMap.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/JavaScriptCore/runtime/WeakGCMap.h	Fri Sep 17 09:02:29 2010 +0300
@@ -0,0 +1,122 @@
+/*
+ * Copyright (C) 2009 Apple Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
+ * THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef WeakGCMap_h
+#define WeakGCMap_h
+
+#include "Collector.h"
+#include <wtf/HashMap.h>
+
+namespace JSC {
+
+class JSCell;
+
+// A HashMap whose get() function returns emptyValue() for cells awaiting destruction.
+template<typename KeyType, typename MappedType>
+class WeakGCMap : public FastAllocBase {
+    /*
+    Invariants:
+        * A value enters the WeakGCMap marked. (Guaranteed by set().)
+        * A value that becomes unmarked leaves the WeakGCMap before being recycled. (Guaranteed by the value's destructor removing it from the WeakGCMap.)
+        * A value that becomes unmarked leaves the WeakGCMap before becoming marked again. (Guaranteed by all destructors running before the mark phase begins.)
+        * During the mark phase, all values in the WeakGCMap are valid. (Guaranteed by all destructors running before the mark phase begins.)
+    */
+
+public:
+    typedef typename HashMap<KeyType, MappedType>::iterator iterator;
+    typedef typename HashMap<KeyType, MappedType>::const_iterator const_iterator;
+    
+    bool isEmpty() { return m_map.isEmpty(); }
+
+    MappedType get(const KeyType& key) const;
+    pair<iterator, bool> set(const KeyType&, const MappedType&); 
+    MappedType take(const KeyType& key);
+
+    // These unchecked functions provide access to a value even if the value's
+    // mark bit is not set. This is used, among other things, to retrieve values
+    // during the GC mark phase, which begins by clearing all mark bits.
+
+    MappedType uncheckedGet(const KeyType& key) const { return m_map.get(key); }
+    bool uncheckedRemove(const KeyType&, const MappedType&);
+
+    iterator uncheckedBegin() { return m_map.begin(); }
+    iterator uncheckedEnd() { return m_map.end(); }
+
+    const_iterator uncheckedBegin() const { return m_map.begin(); }
+    const_iterator uncheckedEnd() const { return m_map.end(); }
+
+private:
+    HashMap<KeyType, MappedType> m_map;
+};
+
+template<typename KeyType, typename MappedType>
+inline MappedType WeakGCMap<KeyType, MappedType>::get(const KeyType& key) const
+{
+    MappedType result = m_map.get(key);
+    if (result == HashTraits<MappedType>::emptyValue())
+        return result;
+    if (!Heap::isCellMarked(result))
+        return HashTraits<MappedType>::emptyValue();
+    return result;
+}
+
+template<typename KeyType, typename MappedType>
+MappedType WeakGCMap<KeyType, MappedType>::take(const KeyType& key)
+{
+    MappedType result = m_map.take(key);
+    if (result == HashTraits<MappedType>::emptyValue())
+        return result;
+    if (!Heap::isCellMarked(result))
+        return HashTraits<MappedType>::emptyValue();
+    return result;
+}
+
+template<typename KeyType, typename MappedType>
+pair<typename HashMap<KeyType, MappedType>::iterator, bool> WeakGCMap<KeyType, MappedType>::set(const KeyType& key, const MappedType& value)
+{
+    Heap::markCell(value); // If value is newly allocated, it's not marked, so mark it now.
+    pair<iterator, bool> result = m_map.add(key, value);
+    if (!result.second) { // pre-existing entry
+        result.second = !Heap::isCellMarked(result.first->second);
+        result.first->second = value;
+    }
+    return result;
+}
+
+template<typename KeyType, typename MappedType>
+bool WeakGCMap<KeyType, MappedType>::uncheckedRemove(const KeyType& key, const MappedType& value)
+{
+    iterator it = m_map.find(key);
+    if (it == m_map.end())
+        return false;
+    if (it->second != value)
+        return false;
+    m_map.remove(it);
+    return true;
+}
+
+} // namespace JSC
+
+#endif // WeakGCMap_h