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+/*
+ * Copyright (C) 2011 Apple Inc. All rights reserved.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ *
+ */
+
+#ifndef StringRecursionChecker_h
+#define StringRecursionChecker_h
+
+#include "Interpreter.h"
+#include <wtf/StackStats.h>
+#include <wtf/WTFThreadData.h>
+
+namespace JSC {
+
+class StringRecursionChecker {
+ WTF_MAKE_NONCOPYABLE(StringRecursionChecker);
+
+public:
+ StringRecursionChecker(ExecState*, JSObject* thisObject);
+ ~StringRecursionChecker();
+
+ JSValue earlyReturnValue() const; // 0 if everything is OK, value to return for failure cases
+
+private:
+ JSValue throwStackOverflowError();
+ JSValue emptyString();
+ JSValue performCheck();
+
+ ExecState* m_exec;
+ JSObject* m_thisObject;
+ JSValue m_earlyReturnValue;
+
+ StackStats::CheckPoint stackCheckpoint;
+};
+
+inline JSValue StringRecursionChecker::performCheck()
+{
+ VM& vm = m_exec->vm();
+ if (!vm.isSafeToRecurse())
+ return throwStackOverflowError();
+
+ bool alreadyVisited = false;
+ if (!vm.stringRecursionCheckFirstObject)
+ vm.stringRecursionCheckFirstObject = m_thisObject;
+ else if (vm.stringRecursionCheckFirstObject == m_thisObject)
+ alreadyVisited = true;
+ else
+ alreadyVisited = !vm.stringRecursionCheckVisitedObjects.add(m_thisObject).isNewEntry;
+
+ if (alreadyVisited)
+ return emptyString(); // Return empty string to avoid infinite recursion.
+ return JSValue(); // Indicate success.
+}
+
+inline StringRecursionChecker::StringRecursionChecker(ExecState* exec, JSObject* thisObject)
+ : m_exec(exec)
+ , m_thisObject(thisObject)
+ , m_earlyReturnValue(performCheck())
+{
+}
+
+inline JSValue StringRecursionChecker::earlyReturnValue() const
+{
+ return m_earlyReturnValue;
+}
+
+inline StringRecursionChecker::~StringRecursionChecker()
+{
+ if (m_earlyReturnValue)
+ return;
+
+ VM& vm = m_exec->vm();
+ if (vm.stringRecursionCheckFirstObject == m_thisObject)
+ vm.stringRecursionCheckFirstObject = nullptr;
+ else {
+ ASSERT(vm.stringRecursionCheckVisitedObjects.contains(m_thisObject));
+ vm.stringRecursionCheckVisitedObjects.remove(m_thisObject);
+ }
+}
+
+}
+
+#endif