Source/JavaScriptCore/bytecode/VariableWatchpointSet.h

/*
 * Copyright (C) 2012, 2013 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
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 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
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 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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#ifndef VariableWatchpointSet_h
#define VariableWatchpointSet_h

#include "Watchpoint.h"
#include "WriteBarrier.h"

namespace JSC {

class VariableWatchpointSet : public WatchpointSet {
    friend class LLIntOffsetsExtractor;
public:
    VariableWatchpointSet()
        : WatchpointSet(ClearWatchpoint)
    {
    }
    
    ~VariableWatchpointSet() { }
    
    // For the purpose of deciding whether or not to watch this variable, you only need
    // to inspect inferredValue(). If this returns something other than the empty
    // value, then it means that at all future safepoints, this watchpoint set will be
    // in one of these states:
    //
    //    IsWatched: in this case, the variable's value must still be the
    //        inferredValue.
    //
    //    IsInvalidated: in this case the variable's value may be anything but you'll
    //        either notice that it's invalidated and not install the watchpoint, or
    //        you will have been notified that the watchpoint was fired.
    JSValue inferredValue() const { return m_inferredValue; }
    
    void notifyWrite(JSValue value)
    {
        ASSERT(!!value);
        switch (state()) {
        case ClearWatchpoint:
            m_inferredValue = value;
            startWatching();
            return;

        case IsWatched:
            ASSERT(!!m_inferredValue);
            if (value == m_inferredValue)
                return;
            invalidate();
            return;
            
        case IsInvalidated:
            ASSERT(!m_inferredValue);
            return;
        }
        
        ASSERT_NOT_REACHED();
    }
    
    void invalidate()
    {
        m_inferredValue = JSValue();
        WatchpointSet::invalidate();
    }
    
    void finalizeUnconditionally()
    {
        ASSERT(!!m_inferredValue == (state() == IsWatched));
        if (!m_inferredValue)
            return;
        if (!m_inferredValue.isCell())
            return;
        JSCell* cell = m_inferredValue.asCell();
        if (Heap::isMarked(cell))
            return;
        invalidate();
    }
    
    JSValue* addressOfInferredValue() { return &m_inferredValue; }

private:
    JSValue m_inferredValue;
};

} // namespace JSC

#endif // VariableWatchpointSet_h