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1 /*
2  * Copyright (C) 2011 Apple Inc. All rights reserved.
3  *
4  * Redistribution and use in source and binary forms, with or without
5  * modification, are permitted provided that the following conditions
6  * are met:
7  * 1. Redistributions of source code must retain the above copyright
8  *    notice, this list of conditions and the following disclaimer.
9  * 2. Redistributions in binary form must reproduce the above copyright
10  *    notice, this list of conditions and the following disclaimer in the
11  *    documentation and/or other materials provided with the distribution.
12  *
13  * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
14  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
15  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
16  * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
17  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
18  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
19  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
20  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
21  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
22  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
23  * THE POSSIBILITY OF SUCH DAMAGE.
24  */
25 
26 #ifndef Handle_h
27 #define Handle_h
28 
29 #include "WriteBarrier.h"
30 #include <wtf/Assertions.h>
31 
32 namespace JSC {
33 
34 /*
35     A Handle is a smart pointer that updates automatically when the garbage
36     collector moves the object to which it points.
37 
38     The base Handle class represents a temporary reference to a pointer whose
39     lifetime is guaranteed by something else.
40 */
41 
42 template <class T> class Handle;
43 
44 // Creating a JSValue Handle is invalid
45 template <> class Handle<JSValue>;
46 
47 // Forward declare WeakGCMap
48 template<typename KeyType, typename MappedType, typename FinalizerCallback, typename HashArg, typename KeyTraitsArg> class WeakGCMap;
49 
50 class HandleBase {
51     friend class HandleHeap;
52     friend struct JSCallbackObjectData;
53     template <typename KeyType, typename MappedType, typename FinalizerCallback, typename HashArg, typename KeyTraitsArg> friend class WeakGCMap;
54 
55 public:
56     bool operator!() const { return !m_slot || !*m_slot; }
57 
58     // This conversion operator allows implicit conversion to bool but not to other integer types.
59     typedef JSValue (HandleBase::*UnspecifiedBoolType);
60     operator UnspecifiedBoolType*() const { return (m_slot && *m_slot) ? reinterpret_cast<UnspecifiedBoolType*>(1) : 0; }
61 
62 protected:
HandleBase(HandleSlot slot)63     HandleBase(HandleSlot slot)
64         : m_slot(slot)
65     {
66     }
67 
swap(HandleBase & other)68     void swap(HandleBase& other) { std::swap(m_slot, other.m_slot); }
69 
slot()70     HandleSlot slot() const { return m_slot; }
setSlot(HandleSlot slot)71     void setSlot(HandleSlot slot)
72     {
73         m_slot = slot;
74     }
75 
76 private:
77     HandleSlot m_slot;
78 };
79 
80 template <typename T> struct HandleTypes {
81     typedef T* ExternalType;
getFromSlotHandleTypes82     static ExternalType getFromSlot(HandleSlot slot) { return (slot && *slot) ? reinterpret_cast<ExternalType>(slot->asCell()) : 0; }
toJSValueHandleTypes83     static JSValue toJSValue(T* cell) { return reinterpret_cast<JSCell*>(cell); }
validateUpcastHandleTypes84     template <typename U> static void validateUpcast() { T* temp; temp = (U*)0; }
85 };
86 
87 template <> struct HandleTypes<Unknown> {
88     typedef JSValue ExternalType;
89     static ExternalType getFromSlot(HandleSlot slot) { return slot ? *slot : JSValue(); }
90     static JSValue toJSValue(const JSValue& v) { return v; }
91     template <typename U> static void validateUpcast() {}
92 };
93 
94 template <typename Base, typename T> struct HandleConverter {
95     T* operator->()
96     {
97 #if ENABLE(JSC_ZOMBIES)
98         ASSERT(!static_cast<const Base*>(this)->get() || !static_cast<const Base*>(this)->get()->isZombie());
99 #endif
100         return static_cast<Base*>(this)->get();
101     }
102     const T* operator->() const
103     {
104 #if ENABLE(JSC_ZOMBIES)
105         ASSERT(!static_cast<const Base*>(this)->get() || !static_cast<const Base*>(this)->get()->isZombie());
106 #endif
107         return static_cast<const Base*>(this)->get();
108     }
109 
110     T* operator*()
111     {
112 #if ENABLE(JSC_ZOMBIES)
113         ASSERT(!static_cast<const Base*>(this)->get() || !static_cast<const Base*>(this)->get()->isZombie());
114 #endif
115         return static_cast<Base*>(this)->get();
116     }
117     const T* operator*() const
118     {
119 #if ENABLE(JSC_ZOMBIES)
120         ASSERT(!static_cast<const Base*>(this)->get() || !static_cast<const Base*>(this)->get()->isZombie());
121 #endif
122         return static_cast<const Base*>(this)->get();
123     }
124 };
125 
126 template <typename Base> struct HandleConverter<Base, Unknown> {
127     Handle<JSObject> asObject() const;
128     bool isObject() const { return jsValue().isObject(); }
129     bool getNumber(double number) const { return jsValue().getNumber(number); }
130     UString getString(ExecState*) const;
131     bool isUndefinedOrNull() const { return jsValue().isUndefinedOrNull(); }
132 
133 private:
134     JSValue jsValue() const
135     {
136 #if ENABLE(JSC_ZOMBIES)
137         ASSERT(!static_cast<const Base*>(this)->get() || !static_cast<const Base*>(this)->get().isZombie());
138 #endif
139         return static_cast<const Base*>(this)->get();
140     }
141 };
142 
143 template <typename T> class Handle : public HandleBase, public HandleConverter<Handle<T>, T> {
144 public:
145     template <typename A, typename B> friend class HandleConverter;
146     typedef typename HandleTypes<T>::ExternalType ExternalType;
147     template <typename U> Handle(Handle<U> o)
148     {
149         typename HandleTypes<T>::template validateUpcast<U>();
150         setSlot(o.slot());
151     }
152 
153     void swap(Handle& other) { HandleBase::swap(other); }
154 
155     ExternalType get() const { return HandleTypes<T>::getFromSlot(this->slot()); }
156 
157 protected:
158     Handle(HandleSlot slot = 0)
159         : HandleBase(slot)
160     {
161     }
162 
163 private:
164     friend class HandleHeap;
165 
166     static Handle<T> wrapSlot(HandleSlot slot)
167     {
168         return Handle<T>(slot);
169     }
170 };
171 
172 template <typename Base> Handle<JSObject> HandleConverter<Base, Unknown>::asObject() const
173 {
174     return Handle<JSObject>::wrapSlot(static_cast<const Base*>(this)->slot());
175 }
176 
177 template <typename T, typename U> inline bool operator==(const Handle<T>& a, const Handle<U>& b)
178 {
179     return a.get() == b.get();
180 }
181 
182 template <typename T, typename U> inline bool operator==(const Handle<T>& a, U* b)
183 {
184     return a.get() == b;
185 }
186 
187 template <typename T, typename U> inline bool operator==(T* a, const Handle<U>& b)
188 {
189     return a == b.get();
190 }
191 
192 template <typename T, typename U> inline bool operator!=(const Handle<T>& a, const Handle<U>& b)
193 {
194     return a.get() != b.get();
195 }
196 
197 template <typename T, typename U> inline bool operator!=(const Handle<T>& a, U* b)
198 {
199     return a.get() != b;
200 }
201 
202 template <typename T, typename U> inline bool operator!=(T* a, const Handle<U>& b)
203 {
204     return a != b.get();
205 }
206 
207 template <typename T, typename U> inline bool operator!=(const Handle<T>& a, JSValue b)
208 {
209     return a.get() != b;
210 }
211 
212 template <typename T, typename U> inline bool operator!=(JSValue a, const Handle<U>& b)
213 {
214     return a != b.get();
215 }
216 
217 }
218 
219 #endif
220