JavaScriptCore-903.tar.gz

[apple/javascriptcore.git] / heap / Weak.h

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+/*
+ * 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 Weak_h
+#define Weak_h
+
+#include "Assertions.h"
+#include "Handle.h"
+#include "HandleHeap.h"
+#include "JSGlobalData.h"
+
+namespace JSC {
+
+// A weakly referenced handle that becomes 0 when the value it points to is garbage collected.
+template <typename T> class Weak : public Handle<T> {
+    using Handle<T>::slot;
+    using Handle<T>::setSlot;
+
+public:
+    typedef typename Handle<T>::ExternalType ExternalType;
+
+    Weak()
+        : Handle<T>()
+    {
+    }
+
+    Weak(JSGlobalData& globalData, ExternalType value = ExternalType(), WeakHandleOwner* weakOwner = 0, void* context = 0)
+        : Handle<T>(globalData.allocateGlobalHandle())
+    {
+        HandleHeap::heapFor(slot())->makeWeak(slot(), weakOwner, context);
+        set(value);
+    }
+
+    enum AdoptTag { Adopt };
+    template<typename U> Weak(AdoptTag, Handle<U> handle)
+        : Handle<T>(handle.slot())
+    {
+        validateCell(get());
+    }
+    
+    Weak(const Weak& other)
+        : Handle<T>()
+    {
+        if (!other.slot())
+            return;
+        setSlot(HandleHeap::heapFor(other.slot())->copyWeak(other.slot()));
+    }
+
+    template <typename U> Weak(const Weak<U>& other)
+        : Handle<T>()
+    {
+        if (!other.slot())
+            return;
+        setSlot(HandleHeap::heapFor(other.slot())->copyWeak(other.slot()));
+    }
+    
+    enum HashTableDeletedValueTag { HashTableDeletedValue };
+    bool isHashTableDeletedValue() const { return slot() == hashTableDeletedValue(); }
+    Weak(HashTableDeletedValueTag)
+        : Handle<T>(hashTableDeletedValue())
+    {
+    }
+
+    ~Weak()
+    {
+        clear();
+    }
+
+    void swap(Weak& other)
+    {
+        Handle<T>::swap(other);
+    }
+
+    ExternalType get() const { return  HandleTypes<T>::getFromSlot(slot()); }
+    
+    void clear()
+    {
+        if (!slot())
+            return;
+        HandleHeap::heapFor(slot())->deallocate(slot());
+        setSlot(0);
+    }
+    
+    void set(JSGlobalData& globalData, ExternalType value, WeakHandleOwner* weakOwner = 0, void* context = 0)
+    {
+        if (!slot()) {
+            setSlot(globalData.allocateGlobalHandle());
+            HandleHeap::heapFor(slot())->makeWeak(slot(), weakOwner, context);
+        }
+        ASSERT(HandleHeap::heapFor(slot())->hasWeakOwner(slot(), weakOwner));
+        set(value);
+    }
+
+    template <typename U> Weak& operator=(const Weak<U>& other)
+    {
+        clear();
+        if (other.slot())
+            setSlot(HandleHeap::heapFor(other.slot())->copyWeak(other.slot()));
+        return *this;
+    }
+
+    Weak& operator=(const Weak& other)
+    {
+        clear();
+        if (other.slot())
+            setSlot(HandleHeap::heapFor(other.slot())->copyWeak(other.slot()));
+        return *this;
+    }
+    
+    HandleSlot leakHandle()
+    {
+        ASSERT(HandleHeap::heapFor(slot())->hasFinalizer(slot()));
+        HandleSlot result = slot();
+        setSlot(0);
+        return result;
+    }
+
+private:
+    static HandleSlot hashTableDeletedValue() { return reinterpret_cast<HandleSlot>(-1); }
+
+    void set(ExternalType externalType)
+    {
+        ASSERT(slot());
+        JSValue value = HandleTypes<T>::toJSValue(externalType);
+        ASSERT(!value || !value.isCell() || Heap::isMarked(value.asCell()));
+        HandleHeap::heapFor(slot())->writeBarrier(slot(), value);
+        *slot() = value;
+    }
+};
+
+template<class T> inline void swap(Weak<T>& a, Weak<T>& b)
+{
+    a.swap(b);
+}
+
+} // namespace JSC
+
+namespace WTF {
+
+template<typename T> struct VectorTraits<JSC::Weak<T> > : SimpleClassVectorTraits {
+    static const bool canCompareWithMemcmp = false;
+};
+
+template<typename P> struct HashTraits<JSC::Weak<P> > : SimpleClassHashTraits<JSC::Weak<P> > { };
+
+}
+
+#endif // Weak_h