runtime/ScopeChain.h

   1 /*
   2  *  Copyright (C) 2003, 2008, 2009 Apple Inc. All rights reserved.
   3  *
   4  *  This library is free software; you can redistribute it and/or
   5  *  modify it under the terms of the GNU Library General Public
   6  *  License as published by the Free Software Foundation; either
   7  *  version 2 of the License, or (at your option) any later version.
   8  *
   9  *  This library is distributed in the hope that it will be useful,
  10  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  *  Library General Public License for more details.
  13  *
  14  *  You should have received a copy of the GNU Library General Public License
  15  *  along with this library; see the file COPYING.LIB.  If not, write to
  16  *  the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  17  *  Boston, MA 02110-1301, USA.
  18  *
  19  */
  20
  21 #ifndef ScopeChain_h
  22 #define ScopeChain_h
  23
  24 #include "FastAllocBase.h"
  25
  26 namespace JSC {
  27
  28     class JSGlobalData;
  29     class JSGlobalObject;
  30     class JSObject;
  31     class MarkStack;
  32     class ScopeChainIterator;
  33
  34     class ScopeChainNode : public FastAllocBase {
  35     public:
  36         ScopeChainNode(ScopeChainNode* next, JSObject* object, JSGlobalData* globalData, JSGlobalObject* globalObject, JSObject* globalThis)
  37             : next(next)
  38             , object(object)
  39             , globalData(globalData)
  40             , globalObject(globalObject)
  41             , globalThis(globalThis)
  42             , refCount(1)
  43         {
  44             ASSERT(globalData);
  45             ASSERT(globalObject);
  46         }
  47 #ifndef NDEBUG
  48         // Due to the number of subtle and timing dependent bugs that have occurred due
  49         // to deleted but still "valid" ScopeChainNodes we now deliberately clobber the
  50         // contents in debug builds.
  51         ~ScopeChainNode()
  52         {
  53             next = 0;
  54             object = 0;
  55             globalData = 0;
  56             globalObject = 0;
  57             globalThis = 0;
  58         }
  59 #endif
  60
  61         ScopeChainNode* next;
  62         JSObject* object;
  63         JSGlobalData* globalData;
  64         JSGlobalObject* globalObject;
  65         JSObject* globalThis;
  66         int refCount;
  67
  68         void deref() { ASSERT(refCount); if (--refCount == 0) { release();} }
  69         void ref() { ASSERT(refCount); ++refCount; }
  70         void release();
  71
  72         // Before calling "push" on a bare ScopeChainNode, a client should
  73         // logically "copy" the node. Later, the client can "deref" the head
  74         // of its chain of ScopeChainNodes to reclaim all the nodes it added
  75         // after the logical copy, leaving nodes added before the logical copy
  76         // (nodes shared with other clients) untouched.
  77         ScopeChainNode* copy()
  78         {
  79             ref();
  80             return this;
  81         }
  82
  83         ScopeChainNode* push(JSObject*);
  84         ScopeChainNode* pop();
  85
  86         ScopeChainIterator begin() const;
  87         ScopeChainIterator end() const;
  88
  89 #ifndef NDEBUG
  90         void print() const;
  91 #endif
  92     };
  93
  94     inline ScopeChainNode* ScopeChainNode::push(JSObject* o)
  95     {
  96         ASSERT(o);
  97         return new ScopeChainNode(this, o, globalData, globalObject, globalThis);
  98     }
  99
 100     inline ScopeChainNode* ScopeChainNode::pop()
 101     {
 102         ASSERT(next);
 103         ScopeChainNode* result = next;
 104
 105         if (--refCount != 0)
 106             ++result->refCount;
 107         else
 108             delete this;
 109
 110         return result;
 111     }
 112
 113     inline void ScopeChainNode::release()
 114     {
 115         // This function is only called by deref(),
 116         // Deref ensures these conditions are true.
 117         ASSERT(refCount == 0);
 118         ScopeChainNode* n = this;
 119         do {
 120             ScopeChainNode* next = n->next;
 121             delete n;
 122             n = next;
 123         } while (n && --n->refCount == 0);
 124     }
 125
 126     class ScopeChainIterator {
 127     public:
 128         ScopeChainIterator(const ScopeChainNode* node)
 129             : m_node(node)
 130         {
 131         }
 132
 133         JSObject* const & operator*() const { return m_node->object; }
 134         JSObject* const * operator->() const { return &(operator*()); }
 135
 136         ScopeChainIterator& operator++() { m_node = m_node->next; return *this; }
 137
 138         // postfix ++ intentionally omitted
 139
 140         bool operator==(const ScopeChainIterator& other) const { return m_node == other.m_node; }
 141         bool operator!=(const ScopeChainIterator& other) const { return m_node != other.m_node; }
 142
 143     private:
 144         const ScopeChainNode* m_node;
 145     };
 146
 147     inline ScopeChainIterator ScopeChainNode::begin() const
 148     {
 149         return ScopeChainIterator(this);
 150     }
 151
 152     inline ScopeChainIterator ScopeChainNode::end() const
 153     {
 154         return ScopeChainIterator(0);
 155     }
 156
 157     class NoScopeChain {};
 158
 159     class ScopeChain {
 160         friend class JIT;
 161     public:
 162         ScopeChain(NoScopeChain)
 163             : m_node(0)
 164         {
 165         }
 166
 167         ScopeChain(JSObject* o, JSGlobalData* globalData, JSGlobalObject* globalObject, JSObject* globalThis)
 168             : m_node(new ScopeChainNode(0, o, globalData, globalObject, globalThis))
 169         {
 170         }
 171
 172         ScopeChain(const ScopeChain& c)
 173             : m_node(c.m_node->copy())
 174         {
 175         }
 176
 177         ScopeChain& operator=(const ScopeChain& c);
 178
 179         explicit ScopeChain(ScopeChainNode* node)
 180             : m_node(node->copy())
 181         {
 182         }
 183
 184         ~ScopeChain()
 185         {
 186             if (m_node)
 187                 m_node->deref();
 188 #ifndef NDEBUG
 189             m_node = 0;
 190 #endif
 191         }
 192
 193         void swap(ScopeChain&);
 194
 195         ScopeChainNode* node() const { return m_node; }
 196
 197         JSObject* top() const { return m_node->object; }
 198
 199         ScopeChainIterator begin() const { return m_node->begin(); }
 200         ScopeChainIterator end() const { return m_node->end(); }
 201
 202         void push(JSObject* o) { m_node = m_node->push(o); }
 203
 204         void pop() { m_node = m_node->pop(); }
 205         void clear() { m_node->deref(); m_node = 0; }
 206
 207         JSGlobalObject* globalObject() const { return m_node->globalObject; }
 208
 209         void markAggregate(MarkStack&) const;
 210
 211         // Caution: this should only be used if the codeblock this is being used
 212         // with needs a full scope chain, otherwise this returns the depth of
 213         // the preceeding call frame
 214         //
 215         // Returns the depth of the current call frame's scope chain
 216         int localDepth() const;
 217
 218 #ifndef NDEBUG
 219         void print() const { m_node->print(); }
 220 #endif
 221
 222     private:
 223         ScopeChainNode* m_node;
 224     };
 225
 226     inline void ScopeChain::swap(ScopeChain& o)
 227     {
 228         ScopeChainNode* tmp = m_node;
 229         m_node = o.m_node;
 230         o.m_node = tmp;
 231     }
 232
 233     inline ScopeChain& ScopeChain::operator=(const ScopeChain& c)
 234     {
 235         ScopeChain tmp(c);
 236         swap(tmp);
 237         return *this;
 238     }
 239
 240 } // namespace JSC
 241
 242 #endif // ScopeChain_h