runtime/SmallStrings.cpp

   1 /*
   2  * Copyright (C) 2008, 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. ``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 #include "config.h"
  27 #include "SmallStrings.h"
  28
  29 #include "HeapRootVisitor.h"
  30 #include "JSGlobalObject.h"
  31 #include "JSString.h"
  32 #include "JSCInlines.h"
  33 #include <wtf/Noncopyable.h>
  34 #include <wtf/PassOwnPtr.h>
  35 #include <wtf/text/StringImpl.h>
  36
  37 namespace JSC {
  38
  39 class SmallStringsStorage {
  40     WTF_MAKE_NONCOPYABLE(SmallStringsStorage); WTF_MAKE_FAST_ALLOCATED;
  41 public:
  42     SmallStringsStorage();
  43
  44     StringImpl* rep(unsigned char character)
  45     {
  46         return m_reps[character].get();
  47     }
  48
  49 private:
  50     static const unsigned singleCharacterStringCount = maxSingleCharacterString + 1;
  51
  52     RefPtr<StringImpl> m_reps[singleCharacterStringCount];
  53 };
  54
  55 SmallStringsStorage::SmallStringsStorage()
  56 {
  57     LChar* characterBuffer = 0;
  58     RefPtr<StringImpl> baseString = StringImpl::createUninitialized(singleCharacterStringCount, characterBuffer);
  59     for (unsigned i = 0; i < singleCharacterStringCount; ++i) {
  60         characterBuffer[i] = i;
  61         m_reps[i] = AtomicString::add(PassRefPtr<StringImpl>(StringImpl::createSubstringSharingImpl(baseString, i, 1)).get());
  62     }
  63 }
  64
  65 SmallStrings::SmallStrings()
  66     : m_emptyString(0)
  67 #define JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE(name) , m_##name(0)
  68     JSC_COMMON_STRINGS_EACH_NAME(JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE)
  69 #undef JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE
  70     , m_nullObjectString(nullptr)
  71     , m_undefinedObjectString(nullptr)
  72 {
  73     COMPILE_ASSERT(singleCharacterStringCount == sizeof(m_singleCharacterStrings) / sizeof(m_singleCharacterStrings[0]), IsNumCharactersConstInSyncWithClassUsage);
  74
  75     for (unsigned i = 0; i < singleCharacterStringCount; ++i)
  76         m_singleCharacterStrings[i] = 0;
  77 }
  78
  79 void SmallStrings::initializeCommonStrings(VM& vm)
  80 {
  81     createEmptyString(&vm);
  82     for (unsigned i = 0; i <= maxSingleCharacterString; ++i)
  83         createSingleCharacterString(&vm, i);
  84 #define JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE(name) initialize(&vm, m_##name, #name);
  85     JSC_COMMON_STRINGS_EACH_NAME(JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE)
  86 #undef JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE
  87     initialize(&vm, m_nullObjectString, "[object Null]");
  88     initialize(&vm, m_undefinedObjectString, "[object Undefined]");
  89 }
  90
  91 void SmallStrings::visitStrongReferences(SlotVisitor& visitor)
  92 {
  93     visitor.appendUnbarrieredPointer(&m_emptyString);
  94     for (unsigned i = 0; i <= maxSingleCharacterString; ++i)
  95         visitor.appendUnbarrieredPointer(m_singleCharacterStrings + i);
  96 #define JSC_COMMON_STRINGS_ATTRIBUTE_VISIT(name) visitor.appendUnbarrieredPointer(&m_##name);
  97     JSC_COMMON_STRINGS_EACH_NAME(JSC_COMMON_STRINGS_ATTRIBUTE_VISIT)
  98 #undef JSC_COMMON_STRINGS_ATTRIBUTE_VISIT
  99     visitor.appendUnbarrieredPointer(&m_nullObjectString);
 100     visitor.appendUnbarrieredPointer(&m_undefinedObjectString);
 101 }
 102
 103 SmallStrings::~SmallStrings()
 104 {
 105 }
 106
 107 void SmallStrings::createEmptyString(VM* vm)
 108 {
 109     ASSERT(!m_emptyString);
 110     m_emptyString = JSString::createHasOtherOwner(*vm, StringImpl::empty());
 111 }
 112
 113 void SmallStrings::createSingleCharacterString(VM* vm, unsigned char character)
 114 {
 115     if (!m_storage)
 116         m_storage = adoptPtr(new SmallStringsStorage);
 117     ASSERT(!m_singleCharacterStrings[character]);
 118     m_singleCharacterStrings[character] = JSString::createHasOtherOwner(*vm, PassRefPtr<StringImpl>(m_storage->rep(character)));
 119 }
 120
 121 StringImpl* SmallStrings::singleCharacterStringRep(unsigned char character)
 122 {
 123     if (!m_storage)
 124         m_storage = adoptPtr(new SmallStringsStorage);
 125     return m_storage->rep(character);
 126 }
 127
 128 void SmallStrings::initialize(VM* vm, JSString*& string, const char* value) const
 129 {
 130     string = JSString::create(*vm, StringImpl::create(value));
 131 }
 132
 133 } // namespace JSC