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diff --git a/Tools/DumpRenderTree/JavaScriptThreading.cpp b/Tools/DumpRenderTree/JavaScriptThreading.cpp
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+++ b/Tools/DumpRenderTree/JavaScriptThreading.cpp
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+/*
+ * Copyright (C) 2005, 2006, 2007 Apple Inc. All rights reserved.
+ *           (C) 2007 Graham Dennis (graham.dennis@gmail.com)
+ *           (C) 2007 Eric Seidel <eric@webkit.org>
+ *           (C) 2012 Patrick Ganstere <paroga@paroga.com>
+ *
+ * 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. 
+ * 3.  Neither the name of Apple Inc. ("Apple") 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 APPLE 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 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.
+ */
+ 
+#include "config.h"
+#include "JavaScriptThreading.h"
+
+#include <JavaScriptCore/JavaScriptCore.h>
+#include <stdlib.h>
+#include <wtf/Assertions.h>
+#include <wtf/HashSet.h>
+#include <wtf/Lock.h>
+#include <wtf/Threading.h>
+#include <wtf/ThreadingPrimitives.h>
+#include <wtf/Vector.h>
+
+static const size_t javaScriptThreadsCount = 4;
+static bool javaScriptThreadsShouldTerminate;
+static JSContextGroupRef javaScriptThreadsGroup;
+
+static Lock& javaScriptThreadsMutex()
+{
+    DEPRECATED_DEFINE_STATIC_LOCAL(Lock, staticMutex, ());
+    return staticMutex;
+}
+
+typedef HashSet<ThreadIdentifier> ThreadSet;
+static ThreadSet& javaScriptThreads()
+{
+    DEPRECATED_DEFINE_STATIC_LOCAL(ThreadSet, staticJavaScriptThreads, ());
+    ASSERT(!javaScriptThreadsMutex().tryLock());
+    return staticJavaScriptThreads;
+}
+
+// This function exercises JSC in a loop until javaScriptThreadsShouldTerminate
+// becomes true or it probabilistically decides to spawn a replacement thread and exit.
+void runJavaScriptThread(void*)
+{
+    static const char* const script =
+        "var array = [];"
+        "for (var i = 0; i < 1024; i++) {"
+        "    array.push(String(i));"
+        "}";
+
+    JSGlobalContextRef ctx;
+    {
+        LockHolder locker(javaScriptThreadsMutex());
+        ctx = JSGlobalContextCreateInGroup(javaScriptThreadsGroup, 0);
+    }
+
+    JSStringRef scriptRef;
+    {
+        LockHolder locker(javaScriptThreadsMutex());
+        scriptRef = JSStringCreateWithUTF8CString(script);
+    }
+
+    while (true) {
+        {
+            LockHolder locker(javaScriptThreadsMutex());
+            JSValueRef exception = 0;
+            JSEvaluateScript(ctx, scriptRef, 0, 0, 1, &exception);
+            ASSERT(!exception);
+        }
+
+        {
+            LockHolder locker(javaScriptThreadsMutex());
+            const size_t valuesCount = 1024;
+            JSValueRef values[valuesCount];
+            for (size_t i = 0; i < valuesCount; ++i)
+                values[i] = JSObjectMake(ctx, 0, 0);
+        }
+
+        {
+            LockHolder locker(javaScriptThreadsMutex());
+            if (javaScriptThreadsShouldTerminate)
+                break;
+        }
+
+        // Respawn probabilistically.
+        if (rand() % 5)
+            continue;
+
+        LockHolder locker(javaScriptThreadsMutex());
+        ThreadIdentifier thread = currentThread();
+        detachThread(thread);
+        javaScriptThreads().remove(thread);
+        javaScriptThreads().add(createThread(&runJavaScriptThread, 0, 0));
+        break;
+    }
+
+    LockHolder locker(javaScriptThreadsMutex());
+    JSStringRelease(scriptRef);
+    JSGarbageCollect(ctx);
+    JSGlobalContextRelease(ctx);
+}
+
+void startJavaScriptThreads()
+{
+    javaScriptThreadsGroup = JSContextGroupCreate();
+
+    LockHolder locker(javaScriptThreadsMutex());
+
+    for (size_t i = 0; i < javaScriptThreadsCount; ++i)
+        javaScriptThreads().add(createThread(&runJavaScriptThread, 0, 0));
+}
+
+void stopJavaScriptThreads()
+{
+    {
+        LockHolder locker(javaScriptThreadsMutex());
+        javaScriptThreadsShouldTerminate = true;
+    }
+
+    Vector<ThreadIdentifier, javaScriptThreadsCount> threads;
+    {
+        LockHolder locker(javaScriptThreadsMutex());
+        copyToVector(javaScriptThreads(), threads);
+        ASSERT(threads.size() == javaScriptThreadsCount);
+    }
+
+    for (size_t i = 0; i < javaScriptThreadsCount; ++i)
+        waitForThreadCompletion(threads[i]);
+
+    {
+        LockHolder locker(javaScriptThreadsMutex());
+        javaScriptThreads().clear();
+    }
+
+    JSContextGroupRelease(javaScriptThreadsGroup);
+}