--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/JavaScriptCore/wtf/CrossThreadRefCounted.h	Fri Sep 17 09:02:29 2010 +0300
@@ -0,0 +1,174 @@
+/*
+ * Copyright (C) 2009 Google Inc. All rights reserved.
+ * Copyright (C) 2010 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:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * 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.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND 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 THE COPYRIGHT
+ * OWNER OR 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 CrossThreadRefCounted_h
+#define CrossThreadRefCounted_h
+
+#include "PassRefPtr.h"
+#include "RefCounted.h"
+#include "Threading.h"
+
+namespace WTF {
+
+    // Used to allowing sharing data across classes and threads (like ThreadedSafeShared).
+    //
+    // Why not just use ThreadSafeShared?
+    // ThreadSafeShared can have a significant perf impact when used in low level classes
+    // (like UString) that get ref/deref'ed a lot. This class has the benefit of doing fast ref
+    // counts like RefPtr whenever possible, but it has the downside that you need to copy it
+    // to use it on another thread.
+    //
+    // Is this class threadsafe?
+    // While each instance of the class is not threadsafe, the copied instance is threadsafe
+    // with respect to the original and any other copies.  The underlying m_data is jointly
+    // owned by the original instance and all copies.
+    template<class T>
+    class CrossThreadRefCounted : public Noncopyable {
+    public:
+        static PassRefPtr<CrossThreadRefCounted<T> > create(T* data)
+        {
+            return adoptRef(new CrossThreadRefCounted<T>(data, 0));
+        }
+
+        // Used to make an instance that can be used on another thread.
+        PassRefPtr<CrossThreadRefCounted<T> > crossThreadCopy();
+
+        void ref();
+        void deref();
+        T* release();
+
+        bool isShared() const
+        {
+            return !m_refCounter.hasOneRef() || (m_threadSafeRefCounter && !m_threadSafeRefCounter->hasOneRef());
+        }
+
+    private:
+        CrossThreadRefCounted(T* data, ThreadSafeSharedBase* threadedCounter)
+            : m_threadSafeRefCounter(threadedCounter)
+            , m_data(data)
+#ifndef NDEBUG
+            , m_threadId(0)
+#endif
+        {
+            // We use RefCountedBase in an unusual way here, so get rid of the requirement
+            // that adoptRef be called on it.
+            m_refCounter.relaxAdoptionRequirement();
+        }
+
+        ~CrossThreadRefCounted()
+        {
+            if (!m_threadSafeRefCounter)
+                delete m_data;
+        }
+
+        void threadSafeDeref();
+
+#ifndef NDEBUG
+        bool isOwnedByCurrentThread() const { return !m_threadId || m_threadId == currentThread(); }
+#endif
+
+        RefCountedBase m_refCounter;
+        ThreadSafeSharedBase* m_threadSafeRefCounter;
+        T* m_data;
+#ifndef NDEBUG
+        ThreadIdentifier m_threadId;
+#endif
+    };
+
+    template<class T>
+    void CrossThreadRefCounted<T>::ref()
+    {
+        ASSERT(isOwnedByCurrentThread());
+        m_refCounter.ref();
+#ifndef NDEBUG
+        // Store the threadId as soon as the ref count gets to 2.
+        // The class gets created with a ref count of 1 and then passed
+        // to another thread where to ref count get increased.  This
+        // is a heuristic but it seems to always work and has helped
+        // find some bugs.
+        if (!m_threadId && m_refCounter.refCount() == 2)
+            m_threadId = currentThread();
+#endif
+    }
+
+    template<class T>
+    void CrossThreadRefCounted<T>::deref()
+    {
+        ASSERT(isOwnedByCurrentThread());
+        if (m_refCounter.derefBase()) {
+            threadSafeDeref();
+            delete this;
+        } else {
+#ifndef NDEBUG
+            // Clear the threadId when the ref goes to 1 because it
+            // is safe to be passed to another thread at this point.
+            if (m_threadId && m_refCounter.refCount() == 1)
+                m_threadId = 0;
+#endif
+        }
+    }
+
+    template<class T>
+    T* CrossThreadRefCounted<T>::release()
+    {
+        ASSERT(!isShared());
+
+        T* data = m_data;
+        m_data = 0;
+        return data;
+    }
+
+    template<class T>
+    PassRefPtr<CrossThreadRefCounted<T> > CrossThreadRefCounted<T>::crossThreadCopy()
+    {
+        ASSERT(isOwnedByCurrentThread());
+        if (m_threadSafeRefCounter)
+            m_threadSafeRefCounter->ref();
+        else
+            m_threadSafeRefCounter = new ThreadSafeSharedBase(2);
+
+        return adoptRef(new CrossThreadRefCounted<T>(m_data, m_threadSafeRefCounter));
+    }
+
+
+    template<class T>
+    void CrossThreadRefCounted<T>::threadSafeDeref()
+    {
+        if (m_threadSafeRefCounter && m_threadSafeRefCounter->derefBase()) {
+            delete m_threadSafeRefCounter;
+            m_threadSafeRefCounter = 0;
+        }
+    }
+} // namespace WTF
+
+using WTF::CrossThreadRefCounted;
+
+#endif // CrossThreadRefCounted_h