Source/JavaScriptCore/runtime/SmallStrings.cpp

/*
 * Copyright (C) 2008, 2010 Apple Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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#include "config.h"
#include "SmallStrings.h"

#include "JSGlobalObject.h"
#include "JSString.h"
#include "JSCInlines.h"
#include <wtf/Noncopyable.h>
#include <wtf/text/StringImpl.h>

namespace JSC {

class SmallStringsStorage {
    WTF_MAKE_NONCOPYABLE(SmallStringsStorage); WTF_MAKE_FAST_ALLOCATED;
public:
    SmallStringsStorage();

    StringImpl& rep(unsigned char character)
    {
        return *m_reps[character].get();
    }

private:
    static const unsigned singleCharacterStringCount = maxSingleCharacterString + 1;

    RefPtr<StringImpl> m_reps[singleCharacterStringCount];
};

SmallStringsStorage::SmallStringsStorage()
{
    LChar* characterBuffer = 0;
    auto baseString = StringImpl::createUninitialized(singleCharacterStringCount, characterBuffer);
    for (unsigned i = 0; i < singleCharacterStringCount; ++i) {
        characterBuffer[i] = i;
        m_reps[i] = AtomicStringImpl::add(StringImpl::createSubstringSharingImpl(baseString.get(), i, 1).ptr());
    }
}

SmallStrings::SmallStrings()
    : m_emptyString(0)
#define JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE(name) , m_##name(0)
    JSC_COMMON_STRINGS_EACH_NAME(JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE)
#undef JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE
    , m_objectStringStart(nullptr)
    , m_nullObjectString(nullptr)
    , m_undefinedObjectString(nullptr)
    , m_needsToBeVisited(true)
{
    COMPILE_ASSERT(singleCharacterStringCount == sizeof(m_singleCharacterStrings) / sizeof(m_singleCharacterStrings[0]), IsNumCharactersConstInSyncWithClassUsage);

    for (unsigned i = 0; i < singleCharacterStringCount; ++i)
        m_singleCharacterStrings[i] = 0;
}

void SmallStrings::initializeCommonStrings(VM& vm)
{
    createEmptyString(&vm);
    for (unsigned i = 0; i <= maxSingleCharacterString; ++i)
        createSingleCharacterString(&vm, i);
#define JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE(name) initialize(&vm, m_##name, #name);
    JSC_COMMON_STRINGS_EACH_NAME(JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE)
#undef JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE
    initialize(&vm, m_objectStringStart, "[object ");
    initialize(&vm, m_nullObjectString, "[object Null]");
    initialize(&vm, m_undefinedObjectString, "[object Undefined]");
}

void SmallStrings::visitStrongReferences(SlotVisitor& visitor)
{
    m_needsToBeVisited = false;
    visitor.appendUnbarriered(m_emptyString);
    for (unsigned i = 0; i <= maxSingleCharacterString; ++i)
        visitor.appendUnbarriered(m_singleCharacterStrings[i]);
#define JSC_COMMON_STRINGS_ATTRIBUTE_VISIT(name) visitor.appendUnbarriered(m_##name);
    JSC_COMMON_STRINGS_EACH_NAME(JSC_COMMON_STRINGS_ATTRIBUTE_VISIT)
#undef JSC_COMMON_STRINGS_ATTRIBUTE_VISIT
    visitor.appendUnbarriered(m_objectStringStart);
    visitor.appendUnbarriered(m_nullObjectString);
    visitor.appendUnbarriered(m_undefinedObjectString);
}

SmallStrings::~SmallStrings()
{
}

void SmallStrings::createEmptyString(VM* vm)
{
    ASSERT(!m_emptyString);
    m_emptyString = JSString::createHasOtherOwner(*vm, *StringImpl::empty());
    ASSERT(m_needsToBeVisited);
}

void SmallStrings::createSingleCharacterString(VM* vm, unsigned char character)
{
    if (!m_storage)
        m_storage = std::make_unique<SmallStringsStorage>();
    ASSERT(!m_singleCharacterStrings[character]);
    m_singleCharacterStrings[character] = JSString::createHasOtherOwner(*vm, m_storage->rep(character));
    ASSERT(m_needsToBeVisited);
}

StringImpl& SmallStrings::singleCharacterStringRep(unsigned char character)
{
    if (!m_storage)
        m_storage = std::make_unique<SmallStringsStorage>();
    return m_storage->rep(character);
}

void SmallStrings::initialize(VM* vm, JSString*& string, const char* value)
{
    string = JSString::create(*vm, AtomicStringImpl::add(value).releaseNonNull());
    ASSERT(m_needsToBeVisited);
}

} // namespace JSC