runtime/StringRecursionChecker.h

   1 /*
   2  *  Copyright (C) 2011 Apple Inc. All rights reserved.
   3  *
   4  *  This library is free software; you can redistribute it and/or
   5  *  modify it under the terms of the GNU Lesser General Public
   6  *  License as published by the Free Software Foundation; either
   7  *  version 2 of the License, or (at your option) any later version.
   8  *
   9  *  This library is distributed in the hope that it will be useful,
  10  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  *  Lesser General Public License for more details.
  13  *
  14  *  You should have received a copy of the GNU Lesser General Public
  15  *  License along with this library; if not, write to the Free Software
  16  *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  17  *
  18  */
  19
  20 #ifndef StringRecursionChecker_h
  21 #define StringRecursionChecker_h
  22
  23 #include "Interpreter.h"
  24 #include <wtf/StackStats.h>
  25 #include <wtf/WTFThreadData.h>
  26
  27 namespace JSC {
  28
  29 class StringRecursionChecker {
  30     WTF_MAKE_NONCOPYABLE(StringRecursionChecker);
  31
  32 public:
  33     StringRecursionChecker(ExecState*, JSObject* thisObject);
  34     ~StringRecursionChecker();
  35
  36     JSValue earlyReturnValue() const; // 0 if everything is OK, value to return for failure cases
  37
  38 private:
  39     JSValue throwStackOverflowError();
  40     JSValue emptyString();
  41     JSValue performCheck();
  42
  43     ExecState* m_exec;
  44     JSObject* m_thisObject;
  45     JSValue m_earlyReturnValue;
  46
  47     StackStats::CheckPoint stackCheckpoint;
  48 };
  49
  50 inline JSValue StringRecursionChecker::performCheck()
  51 {
  52     VM& vm = m_exec->vm();
  53     if (!vm.isSafeToRecurse())
  54         return throwStackOverflowError();
  55     bool alreadyVisited = !vm.stringRecursionCheckVisitedObjects.add(m_thisObject).isNewEntry;
  56     if (alreadyVisited)
  57         return emptyString(); // Return empty string to avoid infinite recursion.
  58     return JSValue(); // Indicate success.
  59 }
  60
  61 inline StringRecursionChecker::StringRecursionChecker(ExecState* exec, JSObject* thisObject)
  62     : m_exec(exec)
  63     , m_thisObject(thisObject)
  64     , m_earlyReturnValue(performCheck())
  65 {
  66 }
  67
  68 inline JSValue StringRecursionChecker::earlyReturnValue() const
  69 {
  70     return m_earlyReturnValue;
  71 }
  72
  73 inline StringRecursionChecker::~StringRecursionChecker()
  74 {
  75     if (m_earlyReturnValue)
  76         return;
  77     ASSERT(m_exec->vm().stringRecursionCheckVisitedObjects.contains(m_thisObject));
  78     m_exec->vm().stringRecursionCheckVisitedObjects.remove(m_thisObject);
  79 }
  80
  81 }
  82
  83 #endif