heap/HandleStack.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 HandleStack_h
  27 #define HandleStack_h
  28
  29 #include <wtf/Assertions.h>
  30 #include <wtf/BlockStack.h>
  31 #include "Handle.h"
  32
  33 #include <wtf/UnusedParam.h>
  34
  35 namespace JSC {
  36
  37 class LocalScope;
  38 class HeapRootVisitor;
  39
  40 class HandleStack {
  41 public:
  42     class Frame {
  43     public:
  44         HandleSlot m_next;
  45         HandleSlot m_end;
  46     };
  47
  48     HandleStack();
  49
  50     void enterScope(Frame&);
  51     void leaveScope(Frame&);
  52
  53     HandleSlot push();
  54
  55     void visit(HeapRootVisitor&);
  56
  57 private:
  58     void grow();
  59     void zapTo(Frame&);
  60     HandleSlot findFirstAfter(HandleSlot);
  61
  62 #ifndef NDEBUG
  63     size_t m_scopeDepth;
  64 #endif
  65     BlockStack<JSValue> m_blockStack;
  66     Frame m_frame;
  67 };
  68
  69 inline void HandleStack::enterScope(Frame& lastFrame)
  70 {
  71 #ifndef NDEBUG
  72     ++m_scopeDepth;
  73 #endif
  74
  75     lastFrame = m_frame;
  76 }
  77
  78
  79
  80 inline void HandleStack::zapTo(Frame& lastFrame)
  81 {
  82 #ifdef NDEBUG
  83     UNUSED_PARAM(lastFrame);
  84 #else
  85     const Vector<HandleSlot>& blocks = m_blockStack.blocks();
  86
  87     if (lastFrame.m_end != m_frame.m_end) { // Zapping to a frame in a different block.
  88         int i = blocks.size() - 1;
  89         for ( ; blocks[i] + m_blockStack.blockLength != lastFrame.m_end; --i) {
  90             for (int j = m_blockStack.blockLength - 1; j >= 0; --j)
  91                 blocks[i][j] = JSValue();
  92         }
  93
  94         for (HandleSlot it = blocks[i] + m_blockStack.blockLength - 1; it != lastFrame.m_next - 1; --it)
  95             *it = JSValue();
  96
  97         return;
  98     }
  99
 100     for (HandleSlot it = m_frame.m_next - 1; it != lastFrame.m_next - 1; --it)
 101         *it = JSValue();
 102 #endif
 103 }
 104
 105 inline void HandleStack::leaveScope(Frame& lastFrame)
 106 {
 107 #ifndef NDEBUG
 108     --m_scopeDepth;
 109 #endif
 110
 111     zapTo(lastFrame);
 112
 113     if (lastFrame.m_end != m_frame.m_end) // Popping to a frame in a different block.
 114         m_blockStack.shrink(lastFrame.m_end);
 115
 116     m_frame = lastFrame;
 117 }
 118
 119 inline HandleSlot HandleStack::push()
 120 {
 121     ASSERT(m_scopeDepth); // Creating a Local outside of a LocalScope is a memory leak.
 122     if (m_frame.m_next == m_frame.m_end)
 123         grow();
 124     return m_frame.m_next++;
 125 }
 126
 127 }
 128
 129 #endif