heap/Local.h

   1 /*
   2  * Copyright (C) 2010 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 Local_h
  27 #define Local_h
  28
  29 #include "Handle.h"
  30 #include "VM.h"
  31
  32 /*
  33     A strongly referenced handle whose lifetime is temporary, limited to a given
  34     LocalScope. Use Locals for local values on the stack. It is an error to
  35     create a Local outside of any LocalScope.
  36 */
  37
  38 namespace JSC {
  39
  40 template <typename T> class Local : public Handle<T> {
  41     friend class LocalScope;
  42     using Handle<T>::slot;
  43
  44 public:
  45     typedef typename Handle<T>::ExternalType ExternalType;
  46
  47     Local(VM&, ExternalType = ExternalType());
  48     Local(VM&, Handle<T>);
  49     Local(const Local<T>&); // Adopting constructor. Used to return a Local to a calling function.
  50
  51     Local& operator=(ExternalType);
  52     Local& operator=(Handle<T>);
  53
  54 private:
  55     Local(HandleSlot, ExternalType); // Used by LocalScope::release() to move a Local to a containing scope.
  56     void set(ExternalType);
  57 };
  58
  59 template <typename T> inline Local<T>::Local(VM& vm, ExternalType value)
  60     : Handle<T>(vm.heap.handleStack()->push())
  61 {
  62     set(value);
  63 }
  64
  65 template <typename T> inline Local<T>::Local(VM& vm, Handle<T> other)
  66     : Handle<T>(vm.heap.handleStack()->push())
  67 {
  68     set(other.get());
  69 }
  70
  71 template <typename T> inline Local<T>::Local(const Local<T>& other)
  72     : Handle<T>(other.slot())
  73 {
  74     const_cast<Local<T>&>(other).setSlot(0); // Prevent accidental sharing.
  75 }
  76
  77 template <typename T> inline Local<T>::Local(HandleSlot slot, ExternalType value)
  78     : Handle<T>(slot, value)
  79 {
  80 }
  81
  82 template <typename T> inline Local<T>& Local<T>::operator=(ExternalType value)
  83 {
  84     set(value);
  85     return *this;
  86 }
  87
  88 template <typename T> inline Local<T>& Local<T>::operator=(Handle<T> other)
  89 {
  90     set(other.get());
  91     return *this;
  92 }
  93
  94 template <typename T> inline void Local<T>::set(ExternalType externalType)
  95 {
  96     ASSERT(slot());
  97     *slot() = externalType;
  98 }
  99
 100
 101 template <typename T, unsigned inlineCapacity = 0> class LocalStack {
 102     typedef typename Handle<T>::ExternalType ExternalType;
 103 public:
 104     LocalStack(VM& vm)
 105         : m_vm(vm)
 106         , m_count(0)
 107     {
 108     }
 109
 110     ExternalType peek() const
 111     {
 112         ASSERT(m_count > 0);
 113         return m_stack[m_count - 1].get();
 114     }
 115
 116     ExternalType pop()
 117     {
 118         ASSERT(m_count > 0);
 119         return m_stack[--m_count].get();
 120     }
 121
 122     void push(ExternalType value)
 123     {
 124         if (m_count == m_stack.size())
 125             m_stack.append(Local<T>(m_vm, value));
 126         else
 127             m_stack[m_count] = value;
 128         m_count++;
 129     }
 130
 131     bool isEmpty() const { return !m_count; }
 132     unsigned size() const { return m_count; }
 133
 134 private:
 135     VM& m_vm;
 136     Vector<Local<T>, inlineCapacity> m_stack;
 137     unsigned m_count;
 138 };
 139
 140 }
 141
 142 namespace WTF {
 143
 144 template<typename T> struct VectorTraits<JSC::Local<T> > : SimpleClassVectorTraits {
 145     static const bool needsDestruction = false;
 146     static const bool canInitializeWithMemset = false;
 147     static const bool canCompareWithMemcmp = false;
 148 };
 149
 150 }
 151
 152 #endif