JavaScriptCore/runtime/WeakGCPtr.h

/*
 * Copyright (C) 2009 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.
 */

#ifndef WeakGCPtr_h
#define WeakGCPtr_h

#include "Collector.h"
#include "GCHandle.h"
#include <wtf/Noncopyable.h>

namespace JSC {

// A smart pointer whose get() function returns 0 for cells awaiting destruction.
template <typename T> class WeakGCPtr : Noncopyable {
public:
    WeakGCPtr()
        : m_ptr(0)
    {
    }

    WeakGCPtr(T* ptr) { assign(ptr); }

    ~WeakGCPtr()
    {
        if (m_ptr)
            m_ptr->pool()->free(m_ptr);
    }

    T* get() const
    {
        if (m_ptr && m_ptr->isValidPtr())
            return static_cast<T*>(m_ptr->get());
        return 0;
    }
    
    bool clear(JSCell* p)
    {
        if (!m_ptr || m_ptr->get() != p)
            return false;

        m_ptr->pool()->free(m_ptr);
        m_ptr = 0;
        return true;
    }

    T& operator*() const { return *get(); }
    T* operator->() const { return get(); }
    
    bool operator!() const { return !get(); }

    // This conversion operator allows implicit conversion to bool but not to other integer types.
#if COMPILER(WINSCW)
    operator bool() const { return m_ptr; }
#else
    typedef WeakGCHandle* WeakGCPtr::*UnspecifiedBoolType;
    operator UnspecifiedBoolType() const { return get() ? &WeakGCPtr::m_ptr : 0; }
#endif

    WeakGCPtr& operator=(T*);

#if !ASSERT_DISABLED
    bool hasDeadObject() const { return !!m_ptr; }
#endif

private:
    void assign(JSCell* ptr)
    {
        ASSERT(ptr);
        if (m_ptr)
            m_ptr->set(ptr);
        else
            m_ptr = Heap::heap(ptr)->addWeakGCHandle(ptr);
    }

    WeakGCHandle* m_ptr;
};

template <typename T> inline WeakGCPtr<T>& WeakGCPtr<T>::operator=(T* optr)
{
    assign(optr);
    return *this;
}

template <typename T, typename U> inline bool operator==(const WeakGCPtr<T>& a, const WeakGCPtr<U>& b)
{ 
    return a.get() == b.get(); 
}

template <typename T, typename U> inline bool operator==(const WeakGCPtr<T>& a, U* b)
{ 
    return a.get() == b; 
}

template <typename T, typename U> inline bool operator==(T* a, const WeakGCPtr<U>& b) 
{
    return a == b.get(); 
}

template <typename T, typename U> inline bool operator!=(const WeakGCPtr<T>& a, const WeakGCPtr<U>& b)
{ 
    return a.get() != b.get(); 
}

template <typename T, typename U> inline bool operator!=(const WeakGCPtr<T>& a, U* b)
{
    return a.get() != b; 
}

template <typename T, typename U> inline bool operator!=(T* a, const WeakGCPtr<U>& b)
{ 
    return a != b.get(); 
}

template <typename T, typename U> inline WeakGCPtr<T> static_pointer_cast(const WeakGCPtr<U>& p)
{ 
    return WeakGCPtr<T>(static_cast<T*>(p.get())); 
}

template <typename T, typename U> inline WeakGCPtr<T> const_pointer_cast(const WeakGCPtr<U>& p)
{ 
    return WeakGCPtr<T>(const_cast<T*>(p.get())); 
}

template <typename T> inline T* get(const WeakGCPtr<T>& p)
{
    return p.get();
}

} // namespace JSC

#endif // WeakGCPtr_h