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/text/StringImpl.h>
  35
  36 namespace JSC {
  37
  38 class SmallStringsStorage {
  39     WTF_MAKE_NONCOPYABLE(SmallStringsStorage); WTF_MAKE_FAST_ALLOCATED;
  40 public:
  41     SmallStringsStorage();
  42
  43     StringImpl* rep(unsigned char character)
  44     {
  45         return m_reps[character].get();
  46     }
  47
  48 private:
  49     static const unsigned singleCharacterStringCount = maxSingleCharacterString + 1;
  50
  51     RefPtr<StringImpl> m_reps[singleCharacterStringCount];
  52 };
  53
  54 SmallStringsStorage::SmallStringsStorage()
  55 {
  56     LChar* characterBuffer = 0;
  57     RefPtr<StringImpl> baseString = StringImpl::createUninitialized(singleCharacterStringCount, characterBuffer);
  58     for (unsigned i = 0; i < singleCharacterStringCount; ++i) {
  59         characterBuffer[i] = i;
  60         m_reps[i] = AtomicStringImpl::add(PassRefPtr<StringImpl>(StringImpl::createSubstringSharingImpl(baseString, i, 1)).get());
  61     }
  62 }
  63
  64 SmallStrings::SmallStrings()
  65     : m_emptyString(0)
  66 #define JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE(name) , m_##name(0)
  67     JSC_COMMON_STRINGS_EACH_NAME(JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE)
  68 #undef JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE
  69     , m_nullObjectString(nullptr)
  70     , m_undefinedObjectString(nullptr)
  71     , m_needsToBeVisited(true)
  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     m_needsToBeVisited = false;
  94     visitor.appendUnbarrieredPointer(&m_emptyString);
  95     for (unsigned i = 0; i <= maxSingleCharacterString; ++i)
  96         visitor.appendUnbarrieredPointer(m_singleCharacterStrings + i);
  97 #define JSC_COMMON_STRINGS_ATTRIBUTE_VISIT(name) visitor.appendUnbarrieredPointer(&m_##name);
  98     JSC_COMMON_STRINGS_EACH_NAME(JSC_COMMON_STRINGS_ATTRIBUTE_VISIT)
  99 #undef JSC_COMMON_STRINGS_ATTRIBUTE_VISIT
 100     visitor.appendUnbarrieredPointer(&m_nullObjectString);
 101     visitor.appendUnbarrieredPointer(&m_undefinedObjectString);
 102 }
 103
 104 SmallStrings::~SmallStrings()
 105 {
 106 }
 107
 108 void SmallStrings::createEmptyString(VM* vm)
 109 {
 110     ASSERT(!m_emptyString);
 111     m_emptyString = JSString::createHasOtherOwner(*vm, StringImpl::empty());
 112     m_needsToBeVisited = true;
 113 }
 114
 115 void SmallStrings::createSingleCharacterString(VM* vm, unsigned char character)
 116 {
 117     if (!m_storage)
 118         m_storage = std::make_unique<SmallStringsStorage>();
 119     ASSERT(!m_singleCharacterStrings[character]);
 120     m_singleCharacterStrings[character] = JSString::createHasOtherOwner(*vm, PassRefPtr<StringImpl>(m_storage->rep(character)));
 121     m_needsToBeVisited = true;
 122 }
 123
 124 StringImpl* SmallStrings::singleCharacterStringRep(unsigned char character)
 125 {
 126     if (!m_storage)
 127         m_storage = std::make_unique<SmallStringsStorage>();
 128     return m_storage->rep(character);
 129 }
 130
 131 void SmallStrings::initialize(VM* vm, JSString*& string, const char* value)
 132 {
 133     string = JSString::create(*vm, Identifier::fromString(vm, value).impl());
 134     m_needsToBeVisited = true;
 135 }
 136
 137 } // namespace JSC