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diff --git a/Source/JavaScriptCore/heap/MarkingConstraintSet.h b/Source/JavaScriptCore/heap/MarkingConstraintSet.h
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+++ b/Source/JavaScriptCore/heap/MarkingConstraintSet.h
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+/*
+ * Copyright (C) 2017 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.
+ */
+
+#pragma once
+
+#include "MarkingConstraint.h"
+#include <wtf/BitVector.h>
+#include <wtf/Vector.h>
+
+namespace JSC {
+
+class MarkingConstraintSet {
+public:
+    MarkingConstraintSet();
+    ~MarkingConstraintSet();
+    
+    void didStartMarking();
+    
+    void add(
+        CString abbreviatedName,
+        CString name,
+        ::Function<void(SlotVisitor&, const VisitingTimeout&)>,
+        ConstraintVolatility);
+    
+    void add(
+        CString abbreviatedName,
+        CString name,
+        ::Function<void(SlotVisitor&, const VisitingTimeout&)>,
+        ::Function<double(SlotVisitor&)>,
+        ConstraintVolatility);
+    
+    void add(std::unique_ptr<MarkingConstraint>);
+    
+    // Assuming that the mark stacks are all empty, this will give you a guess as to whether or
+    // not the wavefront is advancing.
+    bool isWavefrontAdvancing(SlotVisitor&);
+    bool isWavefrontRetreating(SlotVisitor& visitor) { return !isWavefrontAdvancing(visitor); }
+    
+    // Returns true if this executed all constraints and none of them produced new work. This
+    // assumes that you've alraedy visited roots and drained from there.
+    bool executeConvergence(
+        SlotVisitor&,
+        MonotonicTime timeout = MonotonicTime::infinity());
+    
+    // Simply runs all constraints without any shenanigans.
+    void executeAll(SlotVisitor&);
+    
+private:
+    class ExecutionContext;
+    friend class ExecutionContext;
+    
+    bool executeConvergenceImpl(SlotVisitor&, MonotonicTime timeout);
+    
+    bool drain(SlotVisitor&, MonotonicTime, BitVector& unexecuted, BitVector& executed, bool& didVisitSomething);
+    
+    BitVector m_unexecutedRoots;
+    BitVector m_unexecutedOutgrowths;
+    Vector<std::unique_ptr<MarkingConstraint>> m_set;
+    Vector<MarkingConstraint*> m_ordered;
+    Vector<MarkingConstraint*> m_outgrowths;
+    unsigned m_iteration { 1 };
+};
+
+} // namespace JSC
+