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diff --git a/Source/WTF/wtf/ParallelVectorIterator.h b/Source/WTF/wtf/ParallelVectorIterator.h
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+/*
+ * Copyright (C) 2015 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. ``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
+ * 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 ParallelVectorIterator_h
+#define ParallelVectorIterator_h
+
+#include <wtf/FastMalloc.h>
+#include <wtf/Lock.h>
+#include <wtf/Noncopyable.h>
+
+namespace WTF {
+
+template<typename VectorType>
+class ParallelVectorIterator {
+    WTF_MAKE_NONCOPYABLE(ParallelVectorIterator);
+    WTF_MAKE_FAST_ALLOCATED;
+public:
+    ParallelVectorIterator(VectorType& vector, size_t shardSize)
+        : m_vector(vector)
+        , m_shardSize(shardSize)
+    {
+    }
+
+    template<typename Functor>
+    ALWAYS_INLINE void iterate(const Functor& functor)
+    {
+        for (;;) {
+            size_t begin;
+            size_t end;
+            {
+                LockHolder locker(m_lock);
+                begin = m_next;
+                if (begin == m_vector.size())
+                    return;
+                if (m_vector.size() - begin < m_shardSize)
+                    end = m_vector.size();
+                else
+                    end = begin + m_shardSize;
+                RELEASE_ASSERT(end <= m_vector.size());
+                RELEASE_ASSERT(begin < end);
+                m_next = end;
+            }
+
+            for (size_t i = begin; i < end; ++i)
+                functor(m_vector[i]);
+        }
+    }
+private:
+    VectorType& m_vector;
+    Lock m_lock;
+    size_t m_shardSize;
+    size_t m_next { 0 };
+};
+
+} // namespace WTF
+
+using WTF::ParallelVectorIterator;
+
+#endif // ParallelVectorIterator_h
+