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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 WriteBarrier_h
27 #define WriteBarrier_h
28
29 #include "GCAssertions.h"
30 #include "HandleTypes.h"
31 #include "Heap.h"
32 #include "SamplingCounter.h"
33 #include <wtf/TypeTraits.h>
34
35 namespace JSC {
36
37 class JSCell;
38 class VM;
39 class JSGlobalObject;
40
41 template<class T> class WriteBarrierBase;
42 template<> class WriteBarrierBase<JSValue>;
43
44 JS_EXPORT_PRIVATE void slowValidateCell(JSCell*);
45 JS_EXPORT_PRIVATE void slowValidateCell(JSGlobalObject*);
46
47 #if ENABLE(GC_VALIDATION)
48 template<class T> inline void validateCell(T cell)
49 {
50 ASSERT_GC_OBJECT_INHERITS(cell, &WTF::RemovePointer<T>::Type::s_info);
51 }
52
53 template<> inline void validateCell<JSCell*>(JSCell* cell)
54 {
55 slowValidateCell(cell);
56 }
57
58 template<> inline void validateCell<JSGlobalObject*>(JSGlobalObject* globalObject)
59 {
60 slowValidateCell(globalObject);
61 }
62 #else
63 template<class T> inline void validateCell(T)
64 {
65 }
66 #endif
67
68 // We have a separate base class with no constructors for use in Unions.
69 template <typename T> class WriteBarrierBase {
70 public:
71 void set(VM& vm, const JSCell* owner, T* value)
72 {
73 ASSERT(value);
74 validateCell(value);
75 setEarlyValue(vm, owner, value);
76 }
77
78 // This is meant to be used like operator=, but is called copyFrom instead, in
79 // order to kindly inform the C++ compiler that its advice is not appreciated.
80 void copyFrom(const WriteBarrierBase<T>& other)
81 {
82 m_cell = other.m_cell;
83 }
84
85 void setMayBeNull(VM& vm, const JSCell* owner, T* value)
86 {
87 if (value)
88 validateCell(value);
89 setEarlyValue(vm, owner, value);
90 }
91
92 // Should only be used by JSCell during early initialisation
93 // when some basic types aren't yet completely instantiated
94 void setEarlyValue(VM&, const JSCell* owner, T* value)
95 {
96 this->m_cell = reinterpret_cast<JSCell*>(value);
97 Heap::writeBarrier(owner, this->m_cell);
98 }
99
100 T* get() const
101 {
102 // Copy m_cell to a local to avoid multiple-read issues. (See <http://webkit.org/b/110854>)
103 JSCell* cell = m_cell;
104 if (cell)
105 validateCell(cell);
106 return reinterpret_cast<T*>(static_cast<void*>(cell));
107 }
108
109 T* operator*() const
110 {
111 ASSERT(m_cell);
112 validateCell<T>(static_cast<T*>(m_cell));
113 return static_cast<T*>(m_cell);
114 }
115
116 T* operator->() const
117 {
118 ASSERT(m_cell);
119 validateCell(static_cast<T*>(m_cell));
120 return static_cast<T*>(m_cell);
121 }
122
123 void clear() { m_cell = 0; }
124
125 JSCell** slot() { return &m_cell; }
126
127 typedef T* (WriteBarrierBase::*UnspecifiedBoolType);
128 operator UnspecifiedBoolType*() const { return m_cell ? reinterpret_cast<UnspecifiedBoolType*>(1) : 0; }
129
130 bool operator!() const { return !m_cell; }
131
132 void setWithoutWriteBarrier(T* value)
133 {
134 #if ENABLE(WRITE_BARRIER_PROFILING)
135 WriteBarrierCounters::usesWithoutBarrierFromCpp.count();
136 #endif
137 this->m_cell = reinterpret_cast<JSCell*>(value);
138 }
139
140 #if ENABLE(GC_VALIDATION)
141 T* unvalidatedGet() const { return reinterpret_cast<T*>(static_cast<void*>(m_cell)); }
142 #endif
143
144 private:
145 JSCell* m_cell;
146 };
147
148 template <> class WriteBarrierBase<Unknown> {
149 public:
150 void set(VM&, const JSCell* owner, JSValue value)
151 {
152 m_value = JSValue::encode(value);
153 Heap::writeBarrier(owner, value);
154 }
155
156 void setWithoutWriteBarrier(JSValue value)
157 {
158 m_value = JSValue::encode(value);
159 }
160
161 JSValue get() const
162 {
163 return JSValue::decode(m_value);
164 }
165 void clear() { m_value = JSValue::encode(JSValue()); }
166 void setUndefined() { m_value = JSValue::encode(jsUndefined()); }
167 bool isNumber() const { return get().isNumber(); }
168 bool isObject() const { return get().isObject(); }
169 bool isNull() const { return get().isNull(); }
170 bool isGetterSetter() const { return get().isGetterSetter(); }
171
172 JSValue* slot()
173 {
174 union {
175 EncodedJSValue* v;
176 JSValue* slot;
177 } u;
178 u.v = &m_value;
179 return u.slot;
180 }
181
182 int32_t* tagPointer() { return &bitwise_cast<EncodedValueDescriptor*>(&m_value)->asBits.tag; }
183 int32_t* payloadPointer() { return &bitwise_cast<EncodedValueDescriptor*>(&m_value)->asBits.payload; }
184
185 typedef JSValue (WriteBarrierBase::*UnspecifiedBoolType);
186 operator UnspecifiedBoolType*() const { return get() ? reinterpret_cast<UnspecifiedBoolType*>(1) : 0; }
187 bool operator!() const { return !get(); }
188
189 private:
190 EncodedJSValue m_value;
191 };
192
193 template <typename T> class WriteBarrier : public WriteBarrierBase<T> {
194 public:
195 WriteBarrier()
196 {
197 this->setWithoutWriteBarrier(0);
198 }
199
200 WriteBarrier(VM& vm, const JSCell* owner, T* value)
201 {
202 this->set(vm, owner, value);
203 }
204
205 enum MayBeNullTag { MayBeNull };
206 WriteBarrier(VM& vm, const JSCell* owner, T* value, MayBeNullTag)
207 {
208 this->setMayBeNull(vm, owner, value);
209 }
210 };
211
212 template <> class WriteBarrier<Unknown> : public WriteBarrierBase<Unknown> {
213 public:
214 WriteBarrier()
215 {
216 this->setWithoutWriteBarrier(JSValue());
217 }
218
219 WriteBarrier(VM& vm, const JSCell* owner, JSValue value)
220 {
221 this->set(vm, owner, value);
222 }
223 };
224
225 template <typename U, typename V> inline bool operator==(const WriteBarrierBase<U>& lhs, const WriteBarrierBase<V>& rhs)
226 {
227 return lhs.get() == rhs.get();
228 }
229
230 // SlotVisitor functions
231
232 template<typename T> inline void SlotVisitor::append(WriteBarrierBase<T>* slot)
233 {
234 internalAppend(*slot->slot());
235 }
236
237 ALWAYS_INLINE void SlotVisitor::appendValues(WriteBarrierBase<Unknown>* barriers, size_t count)
238 {
239 append(barriers->slot(), count);
240 }
241
242 } // namespace JSC
243
244 #endif // WriteBarrier_h