runtime/WriteBarrier.h

   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 "HandleTypes.h"
  30 #include "Heap.h"
  31 #include "TypeTraits.h"
  32
  33 namespace JSC {
  34
  35 class JSCell;
  36 class JSGlobalData;
  37 class JSGlobalObject;
  38
  39 template<class T> class WriteBarrierBase;
  40 template<> class WriteBarrierBase<JSValue>;
  41
  42 void slowValidateCell(JSCell*);
  43 void slowValidateCell(JSGlobalObject*);
  44
  45 #if ENABLE(GC_VALIDATION)
  46 template<class T> inline void validateCell(T cell)
  47 {
  48     ASSERT_GC_OBJECT_INHERITS(cell, &WTF::RemovePointer<T>::Type::s_info);
  49 }
  50
  51 template<> inline void validateCell<JSCell*>(JSCell* cell)
  52 {
  53     slowValidateCell(cell);
  54 }
  55
  56 template<> inline void validateCell<JSGlobalObject*>(JSGlobalObject* globalObject)
  57 {
  58     slowValidateCell(globalObject);
  59 }
  60 #else
  61 template<class T> inline void validateCell(T)
  62 {
  63 }
  64 #endif
  65
  66 // We have a separate base class with no constructors for use in Unions.
  67 template <typename T> class WriteBarrierBase {
  68 public:
  69     void set(JSGlobalData& globalData, const JSCell* owner, T* value)
  70     {
  71         ASSERT(value);
  72         validateCell(value);
  73         setEarlyValue(globalData, owner, value);
  74     }
  75
  76     void setMayBeNull(JSGlobalData& globalData, const JSCell* owner, T* value)
  77     {
  78         if (value)
  79             validateCell(value);
  80         setEarlyValue(globalData, owner, value);
  81     }
  82
  83     // Should only be used by JSCell during early initialisation
  84     // when some basic types aren't yet completely instantiated
  85     void setEarlyValue(JSGlobalData&, const JSCell* owner, T* value)
  86     {
  87         this->m_cell = reinterpret_cast<JSCell*>(value);
  88         Heap::writeBarrier(owner, this->m_cell);
  89 #if ENABLE(JSC_ZOMBIES)
  90         ASSERT(!isZombie(owner));
  91         ASSERT(!isZombie(m_cell));
  92 #endif
  93     }
  94
  95     T* get() const
  96     {
  97         if (m_cell)
  98             validateCell(m_cell);
  99         return reinterpret_cast<T*>(m_cell);
 100     }
 101
 102     T* operator*() const
 103     {
 104         ASSERT(m_cell);
 105 #if ENABLE(JSC_ZOMBIES)
 106         ASSERT(!isZombie(m_cell));
 107 #endif
 108         validateCell<T>(static_cast<T*>(m_cell));
 109         return static_cast<T*>(m_cell);
 110     }
 111
 112     T* operator->() const
 113     {
 114         ASSERT(m_cell);
 115         validateCell(static_cast<T*>(m_cell));
 116         return static_cast<T*>(m_cell);
 117     }
 118
 119     void clear() { m_cell = 0; }
 120
 121     JSCell** slot() { return &m_cell; }
 122
 123     typedef T* (WriteBarrierBase::*UnspecifiedBoolType);
 124     operator UnspecifiedBoolType*() const { return m_cell ? reinterpret_cast<UnspecifiedBoolType*>(1) : 0; }
 125
 126     bool operator!() const { return !m_cell; }
 127
 128     void setWithoutWriteBarrier(T* value)
 129     {
 130         this->m_cell = reinterpret_cast<JSCell*>(value);
 131 #if ENABLE(JSC_ZOMBIES)
 132         ASSERT(!m_cell || !isZombie(m_cell));
 133 #endif
 134     }
 135
 136 #if ENABLE(GC_VALIDATION)
 137     T* unvalidatedGet() const { return reinterpret_cast<T*>(m_cell); }
 138 #endif
 139
 140 private:
 141     JSCell* m_cell;
 142 };
 143
 144 template <> class WriteBarrierBase<Unknown> {
 145 public:
 146     void set(JSGlobalData&, const JSCell* owner, JSValue value)
 147     {
 148 #if ENABLE(JSC_ZOMBIES)
 149         ASSERT(!isZombie(owner));
 150         ASSERT(!value.isZombie());
 151 #endif
 152         m_value = JSValue::encode(value);
 153         Heap::writeBarrier(owner, value);
 154     }
 155
 156     void setWithoutWriteBarrier(JSValue value)
 157     {
 158 #if ENABLE(JSC_ZOMBIES)
 159         ASSERT(!value.isZombie());
 160 #endif
 161         m_value = JSValue::encode(value);
 162     }
 163
 164     JSValue get() const
 165     {
 166         return JSValue::decode(m_value);
 167     }
 168     void clear() { m_value = JSValue::encode(JSValue()); }
 169     void setUndefined() { m_value = JSValue::encode(jsUndefined()); }
 170     bool isNumber() const { return get().isNumber(); }
 171     bool isObject() const { return get().isObject(); }
 172     bool isNull() const { return get().isNull(); }
 173     bool isGetterSetter() const { return get().isGetterSetter(); }
 174
 175     JSValue* slot()
 176     {
 177         union {
 178             EncodedJSValue* v;
 179             JSValue* slot;
 180         } u;
 181         u.v = &m_value;
 182         return u.slot;
 183     }
 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(JSGlobalData& globalData, const JSCell* owner, T* value)
 201     {
 202         this->set(globalData, owner, value);
 203     }
 204
 205     enum MayBeNullTag { MayBeNull };
 206     WriteBarrier(JSGlobalData& globalData, const JSCell* owner, T* value, MayBeNullTag)
 207     {
 208         this->setMayBeNull(globalData, 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(JSGlobalData& globalData, const JSCell* owner, JSValue value)
 220     {
 221         this->set(globalData, 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 // MarkStack functions
 231
 232 template<typename T> inline void MarkStack::append(WriteBarrierBase<T>* slot)
 233 {
 234     internalAppend(*slot->slot());
 235 }
 236
 237 inline void MarkStack::appendValues(WriteBarrierBase<Unknown>* barriers, size_t count, MarkSetProperties properties)
 238 {
 239     JSValue* values = barriers->slot();
 240 #if ENABLE(GC_VALIDATION)
 241     validateSet(values, count);
 242 #endif
 243     if (count)
 244         m_markSets.append(MarkSet(values, values + count, properties));
 245 }
 246
 247 } // namespace JSC
 248
 249 #endif // WriteBarrier_h