path: root/WebCore/bindings/v8/V8Binding.cpp

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#include "config.h"
#include "V8Binding.h"

#include "AtomicString.h"
#include "CString.h"
#include "MathExtras.h"
#include "PlatformString.h"
#include "StdLibExtras.h"
#include "StringBuffer.h"
#include "StringHash.h"
#include "Threading.h"

#include <v8.h>

namespace WebCore {

// WebCoreStringResource is a helper class for v8ExternalString. It is used
// to manage the life-cycle of the underlying buffer of the external string.
class WebCoreStringResource : public v8::String::ExternalStringResource {
public:
    explicit WebCoreStringResource(const String& string)
        : m_plainString(string)
    {
#ifndef NDEBUG
        m_threadId = WTF::currentThread();
#endif
        v8::V8::AdjustAmountOfExternalAllocatedMemory(2 * length());
    }

    explicit WebCoreStringResource(const AtomicString& string)
        : m_plainString(string)
        , m_atomicString(string)
    {
#ifndef NDEBUG
        m_threadId = WTF::currentThread();
#endif
        v8::V8::AdjustAmountOfExternalAllocatedMemory(2 * length());
    }

    virtual ~WebCoreStringResource()
    {
#ifndef NDEBUG
        ASSERT(m_threadId == WTF::currentThread());
#endif
        int reducedExternalMemory = -2 * length();
        if (!m_plainString.impl()->inTable())
            reducedExternalMemory *= 2;
        v8::V8::AdjustAmountOfExternalAllocatedMemory(reducedExternalMemory);
    }

    const uint16_t* data() const
    {
        return reinterpret_cast<const uint16_t*>(m_plainString.characters());
    }

    size_t length() const { return m_plainString.length(); }

    String webcoreString() { return m_plainString; }

    AtomicString atomicString()
    {
#ifndef NDEBUG
        ASSERT(m_threadId == WTF::currentThread());
#endif
        if (m_atomicString.isNull()) {
            m_atomicString = AtomicString(m_plainString);
            if (!m_plainString.impl()->inTable())
                v8::V8::AdjustAmountOfExternalAllocatedMemory(2 * length());
        }
        return m_atomicString;
    }

    static WebCoreStringResource* toStringResource(v8::Handle<v8::String> v8String)
    {
        return static_cast<WebCoreStringResource*>(v8String->GetExternalStringResource());
    }

private:
    // A shallow copy of the string. Keeps the string buffer alive until the V8 engine garbage collects it.
    String m_plainString;
    // If this string is atomic or has been made atomic earlier the
    // atomic string is held here. In the case where the string starts
    // off non-atomic and becomes atomic later it is necessary to keep
    // the original string alive because v8 may keep derived pointers
    // into that string.
    AtomicString m_atomicString;

#ifndef NDEBUG
    WTF::ThreadIdentifier m_threadId;
#endif
};

String v8StringToWebCoreString(v8::Handle<v8::String> v8String, ExternalMode external,
        StringType type)
{
    WebCoreStringResource* stringResource = WebCoreStringResource::toStringResource(v8String);
    if (stringResource)
        return stringResource->webcoreString();

    int length = v8String->Length();
    if (!length) {
        // Avoid trying to morph empty strings, as they do not have enough room to contain the external reference.
        return StringImpl::empty();
    }

    UChar* buffer;
    String result = String::createUninitialized(length, buffer);
    v8String->Write(reinterpret_cast<uint16_t*>(buffer), 0, length);

    if (type == AtomicStringType)
        result = AtomicString(result);

    if (external == Externalize) {
        WebCoreStringResource* resource = new WebCoreStringResource(result);
        if (!v8String->MakeExternal(resource)) {
            // In case of a failure delete the external resource as it was not used.
            delete resource;
        }
    }
    return result;
}

AtomicString v8StringToAtomicWebCoreString(v8::Handle<v8::String> v8String)
{
    WebCoreStringResource* stringResource = WebCoreStringResource::toStringResource(v8String);
    if (!stringResource) {
        if (!v8String->CanMakeExternal())
            return v8StringToWebCoreString(v8String, DoNotExternalize, AtomicStringType);
        // If this string hasn't been externalized, we force it now.
        v8StringToWebCoreString(v8String, Externalize, AtomicStringType);
        stringResource = WebCoreStringResource::toStringResource(v8String);
        ASSERT(stringResource);
    }
    return stringResource->atomicString();
}

String v8ValueToWebCoreString(v8::Handle<v8::Value> object)
{
    if (object->IsString())
        return v8StringToWebCoreString(v8::Handle<v8::String>::Cast(object), Externalize, PlainStringType);

    if (object->IsInt32()) {
        int value = object->Int32Value();
        // Most numbers used are <= 100. Even if they aren't used there's very little in using the space.
        const int kLowNumbers = 100;
        static AtomicString lowNumbers[kLowNumbers + 1];
        String webCoreString;
        if (0 <= value && value <= kLowNumbers) {
            webCoreString = lowNumbers[value];
            if (!webCoreString) {
                AtomicString valueString = AtomicString(String::number(value));
                lowNumbers[value] = valueString;
                webCoreString = valueString;
            }
        } else
            webCoreString = String::number(value);
        return webCoreString;
    }

    v8::TryCatch block;
    v8::Handle<v8::String> v8String = object->ToString();
    // Check for empty handles to handle the case where an exception
    // is thrown as part of invoking toString on the objectect.
    if (v8String.IsEmpty())
        return StringImpl::empty();
    return v8StringToWebCoreString(v8String, DoNotExternalize, PlainStringType);
}

AtomicString v8ValueToAtomicWebCoreString(v8::Handle<v8::Value> v8Value)
{
    if (v8Value->IsString())
        return v8StringToAtomicWebCoreString(v8::Handle<v8::String>::Cast(v8Value));
    String string = v8ValueToWebCoreString(v8Value);
    return AtomicString(string);
}

v8::Handle<v8::String> v8String(const String& string)
{
    return v8ExternalString(string);
}

static bool stringImplCacheEnabled = false;

void enableStringImplCache()
{
    stringImplCacheEnabled = true;
}

static v8::Local<v8::String> makeExternalString(const String& string)
{
    WebCoreStringResource* stringResource = new WebCoreStringResource(string);
    v8::Local<v8::String> newString = v8::String::NewExternal(stringResource);
    if (newString.IsEmpty())
        delete stringResource;

    return newString;
}

typedef HashMap<StringImpl*, v8::String*> StringCache;

static StringCache& getStringCache()
{
    ASSERT(WTF::isMainThread());
    DEFINE_STATIC_LOCAL(StringCache, mainThreadStringCache, ());
    return mainThreadStringCache;
}

static void cachedStringCallback(v8::Persistent<v8::Value> wrapper, void* parameter)
{
    ASSERT(WTF::isMainThread());
    StringImpl* stringImpl = static_cast<StringImpl*>(parameter);
    ASSERT(getStringCache().contains(stringImpl));
    getStringCache().remove(stringImpl);
    wrapper.Dispose();
    stringImpl->deref();
}

v8::Local<v8::String> v8ExternalString(const String& string)
{
    if (!string.length())
        return v8::String::Empty();

    if (!stringImplCacheEnabled)
        return makeExternalString(string);

    StringImpl* stringImpl = string.impl();
    StringCache& stringCache = getStringCache();
    v8::String* cachedV8String = stringCache.get(stringImpl);
    if (cachedV8String)
        return v8::Local<v8::String>(cachedV8String);

    v8::Local<v8::String> newString = makeExternalString(string);
    if (newString.IsEmpty())
        return newString;

    v8::Persistent<v8::String> wrapper = v8::Persistent<v8::String>::New(newString);
    if (wrapper.IsEmpty())
        return newString;

    stringImpl->ref();
    wrapper.MakeWeak(stringImpl, cachedStringCallback);
    stringCache.set(stringImpl, *wrapper);

    return newString;
}

} // namespace WebCore