runtime/ArrayStorage.h

   1 /*
   2  * Copyright (C) 2012 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. ``AS IS'' AND ANY
  14  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  15  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  16  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  17  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  18  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  19  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  20  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  21  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  23  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #ifndef ArrayStorage_h
  27 #define ArrayStorage_h
  28
  29 #include "ArrayConventions.h"
  30 #include "Butterfly.h"
  31 #include "IndexingHeader.h"
  32 #include "SparseArrayValueMap.h"
  33 #include "WriteBarrier.h"
  34 #include <wtf/Noncopyable.h>
  35 #include <wtf/Platform.h>
  36
  37 namespace JSC {
  38
  39 // This struct holds the actual data values of an array. A JSArray object points to its contained ArrayStorage
  40 // struct by pointing to m_vector. To access the contained ArrayStorage struct, use the getStorage() and
  41 // setStorage() methods. It is important to note that there may be space before the ArrayStorage that
  42 // is used to quick unshift / shift operation. The actual allocated pointer is available by using:
  43 //     getStorage() - m_indexBias * sizeof(JSValue)
  44 // All slots in ArrayStorage (slots from 0 to vectorLength) are expected to be initialized to a JSValue or,
  45 // for hole slots, JSValue().
  46 struct ArrayStorage {
  47     WTF_MAKE_NONCOPYABLE(ArrayStorage);
  48 private:
  49     ArrayStorage() { } // Not directly instantiable. Can only be created as part of a Butterfly.
  50 public:
  51
  52     static ArrayStorage* from(Butterfly* butterfly) { return reinterpret_cast_ptr<ArrayStorage*>(butterfly); }
  53     static ArrayStorage* from(IndexingHeader* indexingHeader) { return indexingHeader->arrayStorage(); }
  54
  55     Butterfly* butterfly() { return reinterpret_cast<Butterfly*>(this); }
  56     IndexingHeader* indexingHeader() { return IndexingHeader::from(this); }
  57
  58     // We steal two fields from the indexing header: vectorLength and length.
  59     unsigned length() { return indexingHeader()->publicLength(); }
  60     void setLength(unsigned length) { indexingHeader()->setPublicLength(length); }
  61     unsigned vectorLength() { return indexingHeader()->vectorLength(); }
  62     void setVectorLength(unsigned length) { indexingHeader()->setVectorLength(length); }
  63
  64     ALWAYS_INLINE void copyHeaderFromDuringGC(const ArrayStorage& other)
  65     {
  66         m_sparseMap.copyFrom(other.m_sparseMap);
  67         m_indexBias = other.m_indexBias;
  68         m_numValuesInVector = other.m_numValuesInVector;
  69     }
  70
  71     bool inSparseMode()
  72     {
  73         return m_sparseMap && m_sparseMap->sparseMode();
  74     }
  75
  76     ContiguousJSValues vector() { return ContiguousJSValues(m_vector, vectorLength()); }
  77
  78     WriteBarrier<SparseArrayValueMap> m_sparseMap;
  79     unsigned m_indexBias;
  80     unsigned m_numValuesInVector;
  81 #if USE(JSVALUE32_64)
  82     uintptr_t m_padding;
  83 #endif
  84     WriteBarrier<Unknown> m_vector[1];
  85
  86     static ptrdiff_t lengthOffset() { return Butterfly::offsetOfPublicLength(); }
  87     static ptrdiff_t vectorLengthOffset() { return Butterfly::offsetOfVectorLength(); }
  88     static ptrdiff_t numValuesInVectorOffset() { return OBJECT_OFFSETOF(ArrayStorage, m_numValuesInVector); }
  89     static ptrdiff_t vectorOffset() { return OBJECT_OFFSETOF(ArrayStorage, m_vector); }
  90     static ptrdiff_t indexBiasOffset() { return OBJECT_OFFSETOF(ArrayStorage, m_indexBias); }
  91     static ptrdiff_t sparseMapOffset() { return OBJECT_OFFSETOF(ArrayStorage, m_sparseMap); }
  92
  93     static size_t sizeFor(unsigned vectorLength)
  94     {
  95         return ArrayStorage::vectorOffset() + vectorLength * sizeof(WriteBarrier<Unknown>);
  96     }
  97 };
  98
  99 } // namespace JSC
 100
 101 #endif // ArrayStorage_h
 102