UStringImpl.h   [plain text]

/*
 * Copyright (C) 2009 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,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
 */

#ifndef UStringImpl_h
#define UStringImpl_h

#include <limits>
#include <wtf/CrossThreadRefCounted.h>
#include <wtf/OwnFastMallocPtr.h>
#include <wtf/PossiblyNull.h>
#include <wtf/StringHashFunctions.h>
#include <wtf/Vector.h>
#include <wtf/unicode/Unicode.h>

namespace JSC {

class IdentifierTable;
  
typedef CrossThreadRefCounted<OwnFastMallocPtr<UChar> > SharedUChar;

class UntypedPtrAndBitfield {
public:
    UntypedPtrAndBitfield() {}

    UntypedPtrAndBitfield(void* ptrValue, uintptr_t bitValue)
        : m_value(reinterpret_cast<uintptr_t>(ptrValue) | bitValue)
#ifndef NDEBUG
        , m_leaksPtr(ptrValue)
#endif
    {
        ASSERT(ptrValue == asPtr<void*>());
        ASSERT((*this & ~s_alignmentMask) == bitValue);
    }

    template<typename T>
    T asPtr() const { return reinterpret_cast<T>(m_value & s_alignmentMask); }

    UntypedPtrAndBitfield& operator&=(uintptr_t bits)
    {
        m_value &= bits | s_alignmentMask;
        return *this;
    }

    UntypedPtrAndBitfield& operator|=(uintptr_t bits)
    {
        m_value |= bits & ~s_alignmentMask;
        return *this;
    }

    uintptr_t operator&(uintptr_t mask) const
    {
        return m_value & mask & ~s_alignmentMask;
    }

private:
    static const uintptr_t s_alignmentMask = ~static_cast<uintptr_t>(0x7);
    uintptr_t m_value;
#ifndef NDEBUG
        void* m_leaksPtr; // Only used to allow tools like leaks on OSX to detect that the memory is referenced.
#endif
};

class UStringImpl : Noncopyable {
public:
    template<size_t inlineCapacity>
    static PassRefPtr<UStringImpl> adopt(Vector<UChar, inlineCapacity>& vector)
    {
        if (unsigned length = vector.size())
            return adoptRef(new UStringImpl(vector.releaseBuffer(), length, BufferOwned));
        return &empty();
    }

    static PassRefPtr<UStringImpl> create(const UChar* buffer, int length)
    {
        UChar* newBuffer;
        if (PassRefPtr<UStringImpl> impl = tryCreateUninitialized(length, newBuffer)) {
            copyChars(newBuffer, buffer, length);
            return impl;
        }
        return &null();
    }

    static PassRefPtr<UStringImpl> create(PassRefPtr<UStringImpl> rep, int offset, int length)
    {
        ASSERT(rep);
        rep->checkConsistency();
        return adoptRef(new UStringImpl(rep->m_data + offset, length, rep->bufferOwnerString()));
    }

    static PassRefPtr<UStringImpl> create(PassRefPtr<SharedUChar> sharedBuffer, UChar* buffer, int length)
    {
        return adoptRef(new UStringImpl(buffer, length, sharedBuffer));
    }

    static PassRefPtr<UStringImpl> createUninitialized(unsigned length, UChar*& output)
    {
        if (!length) {
            output = 0;
            return &empty();
        }

        if (length > ((std::numeric_limits<size_t>::max() - sizeof(UStringImpl)) / sizeof(UChar)))
            CRASH();
        UStringImpl* resultImpl = static_cast<UStringImpl*>(fastMalloc(sizeof(UChar) * length + sizeof(UStringImpl)));
        output = reinterpret_cast<UChar*>(resultImpl + 1);
        return adoptRef(new(resultImpl) UStringImpl(output, length, BufferInternal));
    }

    static PassRefPtr<UStringImpl> tryCreateUninitialized(unsigned length, UChar*& output)
    {
        if (!length) {
            output = 0;
            return &empty();
        }

        if (length > ((std::numeric_limits<size_t>::max() - sizeof(UStringImpl)) / sizeof(UChar)))
            return 0;
        UStringImpl* resultImpl;
        if (!tryFastMalloc(sizeof(UChar) * length + sizeof(UStringImpl)).getValue(resultImpl))
            return 0;
        output = reinterpret_cast<UChar*>(resultImpl + 1);
        return adoptRef(new(resultImpl) UStringImpl(output, length, BufferInternal));
    }

    SharedUChar* sharedBuffer();
    UChar* data() const { return m_data; }
    int size() const { return m_length; }
    size_t cost()
    {
        // For substrings, return the cost of the base string.
        if (bufferOwnership() == BufferSubstring)
            return m_dataBuffer.asPtr<UStringImpl*>()->cost();

        if (m_dataBuffer & s_reportedCostBit)
            return 0;
        m_dataBuffer |= s_reportedCostBit;
        return m_length;
    }
    unsigned hash() const { if (!m_hash) m_hash = computeHash(data(), m_length); return m_hash; }
    unsigned existingHash() const { ASSERT(m_hash); return m_hash; } // fast path for Identifiers
    void setHash(unsigned hash) { ASSERT(hash == computeHash(data(), m_length)); m_hash = hash; } // fast path for Identifiers
    bool isIdentifier() const { return m_isIdentifier; }
    void setIsIdentifier(bool isIdentifier) { m_isIdentifier = isIdentifier; }

    UStringImpl* ref() { m_refCount += s_refCountIncrement; return this; }
    ALWAYS_INLINE void deref() { if (!(m_refCount -= s_refCountIncrement)) delete this; }

    static void copyChars(UChar* destination, const UChar* source, unsigned numCharacters)
    {
        if (numCharacters <= s_copyCharsInlineCutOff) {
            for (unsigned i = 0; i < numCharacters; ++i)
                destination[i] = source[i];
        } else
            memcpy(destination, source, numCharacters * sizeof(UChar));
    }

    static unsigned computeHash(const UChar* s, int length) { ASSERT(length >= 0); return WTF::stringHash(s, length); }
    static unsigned computeHash(const char* s, int length) { ASSERT(length >= 0); return WTF::stringHash(s, length); }
    static unsigned computeHash(const char* s) { return WTF::stringHash(s); }

    static UStringImpl& null() { return *s_null; }
    static UStringImpl& empty() { return *s_empty; }

    ALWAYS_INLINE void checkConsistency() const
    {
        // There is no recursion of substrings.
        ASSERT(bufferOwnerString()->bufferOwnership() != BufferSubstring);
        // Static strings cannot be put in identifier tables, because they are globally shared.
        ASSERT(!isStatic() || !isIdentifier());
    }

private:
    enum BufferOwnership {
        BufferInternal,
        BufferOwned,
        BufferSubstring,
        BufferShared,
    };

    // For SmallStringStorage, which allocates an array and uses an in-place new.
    UStringImpl() { }

    // Used to construct normal strings with an internal or external buffer.
    UStringImpl(UChar* data, int length, BufferOwnership ownership)
        : m_data(data)
        , m_length(length)
        , m_refCount(s_refCountIncrement)
        , m_hash(0)
        , m_isIdentifier(false)
        , m_dataBuffer(0, ownership)
    {
        ASSERT((ownership == BufferInternal) || (ownership == BufferOwned));
        checkConsistency();
    }

    // Used to construct static strings, which have an special refCount that can never hit zero.
    // This means that the static string will never be destroyed, which is important because
    // static strings will be shared across threads & ref-counted in a non-threadsafe manner.
    enum StaticStringConstructType { ConstructStaticString };
    UStringImpl(UChar* data, int length, StaticStringConstructType)
        : m_data(data)
        , m_length(length)
        , m_refCount(s_staticRefCountInitialValue)
        , m_hash(0)
        , m_isIdentifier(false)
        , m_dataBuffer(0, BufferOwned)
    {
        checkConsistency();
    }

    // Used to create new strings that are a substring of an existing string.
    UStringImpl(UChar* data, int length, PassRefPtr<UStringImpl> base)
        : m_data(data)
        , m_length(length)
        , m_refCount(s_refCountIncrement)
        , m_hash(0)
        , m_isIdentifier(false)
        , m_dataBuffer(base.releaseRef(), BufferSubstring)
    {
        // Do use static strings as a base for substrings; UntypedPtrAndBitfield assumes
        // that all pointers will be at least 8-byte aligned, we cannot guarantee that of
        // UStringImpls that are not heap allocated.
        ASSERT(m_dataBuffer.asPtr<UStringImpl*>()->size());
        ASSERT(!m_dataBuffer.asPtr<UStringImpl*>()->isStatic());
        checkConsistency();
    }

    // Used to construct new strings sharing an existing shared buffer.
    UStringImpl(UChar* data, int length, PassRefPtr<SharedUChar> sharedBuffer)
        : m_data(data)
        , m_length(length)
        , m_refCount(s_refCountIncrement)
        , m_hash(0)
        , m_isIdentifier(false)
        , m_dataBuffer(sharedBuffer.releaseRef(), BufferShared)
    {
        checkConsistency();
    }

    using Noncopyable::operator new;
    void* operator new(size_t, void* inPlace) { return inPlace; }

    ~UStringImpl();

    // This number must be at least 2 to avoid sharing empty, null as well as 1 character strings from SmallStrings.
    static const int s_minLengthToShare = 10;
    static const unsigned s_copyCharsInlineCutOff = 20;
    static const uintptr_t s_bufferOwnershipMask = 3;
    static const uintptr_t s_reportedCostBit = 4;
    // We initialize and increment/decrement the refCount for all normal (non-static) strings by the value 2.
    // We initialize static strings with an odd number (specifically, 1), such that the refCount cannot reach zero.
    static const int s_refCountIncrement = 2;
    static const int s_staticRefCountInitialValue = 1;

    UStringImpl* bufferOwnerString() { return (bufferOwnership() == BufferSubstring) ? m_dataBuffer.asPtr<UStringImpl*>() :  this; }
    const UStringImpl* bufferOwnerString() const { return (bufferOwnership() == BufferSubstring) ? m_dataBuffer.asPtr<UStringImpl*>() :  this; }
    SharedUChar* baseSharedBuffer();
    unsigned bufferOwnership() const { return m_dataBuffer & s_bufferOwnershipMask; }
    bool isStatic() const { return m_refCount & 1; }

    // unshared data
    UChar* m_data;
    int m_length;
    unsigned m_refCount;
    mutable unsigned m_hash : 31;
    mutable unsigned m_isIdentifier : 1;
    UntypedPtrAndBitfield m_dataBuffer;

    JS_EXPORTDATA static UStringImpl* s_null;
    JS_EXPORTDATA static UStringImpl* s_empty;

    friend class JIT;
    friend class SmallStringsStorage;
    friend void initializeUString();
};

bool equal(const UStringImpl*, const UStringImpl*);

}

#endif