CrossThreadCopier.h

/*
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * 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.
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 * this software without specific prior written permission.
 *
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 */

#ifndef CrossThreadCopier_h
#define CrossThreadCopier_h

#include <wtf/Assertions.h>
#include <wtf/Forward.h>
#include <wtf/PassOwnPtr.h>
#include <wtf/PassRefPtr.h>
#include <wtf/RefPtr.h>
#include <wtf/Threading.h>
#include <wtf/TypeTraits.h>

namespace WebCore {

    class IntRect;
    class IntSize;
    class KURL;
    class ResourceError;
    class ResourceRequest;
    class ResourceResponse;
    struct CrossThreadResourceResponseData;
    struct CrossThreadResourceRequestData;
    struct ThreadableLoaderOptions;

    template<typename T> struct CrossThreadCopierPassThrough {
        typedef T Type;
        static Type copy(const T& parameter)
        {
            return parameter;
        }
    };

    template<bool isConvertibleToInteger, bool isThreadSafeRefCounted, typename T> struct CrossThreadCopierBase;

    // Integers get passed through without any changes.
    template<typename T> struct CrossThreadCopierBase<true, false, T> : public CrossThreadCopierPassThrough<T> {
    };

    // To allow a type to be passed across threads using its copy constructor, add a forward declaration of the type and
    // a CopyThreadCopierBase<false, false, TypeName> : public CrossThreadCopierPassThrough<TypeName> { }; to this file.
    template<> struct CrossThreadCopierBase<false, false, ThreadableLoaderOptions> : public CrossThreadCopierPassThrough<ThreadableLoaderOptions> {
    };

    template<> struct CrossThreadCopierBase<false, false, IntRect> : public CrossThreadCopierPassThrough<IntRect> {
    };

    template<> struct CrossThreadCopierBase<false, false, IntSize> : public CrossThreadCopierPassThrough<IntSize> {
    };

    // Custom copy methods.
    template<typename T> struct CrossThreadCopierBase<false, true, T> {
        typedef typename WTF::RemoveTemplate<T, RefPtr>::Type TypeWithoutRefPtr;
        typedef typename WTF::RemoveTemplate<TypeWithoutRefPtr, PassRefPtr>::Type TypeWithoutPassRefPtr;
        typedef typename WTF::RemovePointer<TypeWithoutPassRefPtr>::Type RefCountedType;

        // Verify that only one of the above did a change.
        COMPILE_ASSERT((WTF::IsSameType<RefPtr<RefCountedType>, T>::value
                        || WTF::IsSameType<PassRefPtr<RefCountedType>, T>::value
                        || WTF::IsSameType<RefCountedType*, T>::value),
                       OnlyAllowOneTypeModification);

        typedef PassRefPtr<RefCountedType> Type;
        static Type copy(const T& refPtr)
        {
            return refPtr;
        }
    };

    template<typename T> struct CrossThreadCopierBase<false, false, PassOwnPtr<T> > {
        typedef PassOwnPtr<T> Type;
        static Type copy(Type ownPtr)
        {
            return ownPtr;
        }
    };

    template<> struct CrossThreadCopierBase<false, false, KURL> {
        typedef KURL Type;
        static Type copy(const KURL&);
    };

    template<> struct CrossThreadCopierBase<false, false, String> {
        typedef String Type;
        static Type copy(const String&);
    };

    template<> struct CrossThreadCopierBase<false, false, ResourceError> {
        typedef ResourceError Type;
        static Type copy(const ResourceError&);
    };

    template<> struct CrossThreadCopierBase<false, false, ResourceRequest> {
        typedef PassOwnPtr<CrossThreadResourceRequestData> Type;
        static Type copy(const ResourceRequest&);
    };

    template<> struct CrossThreadCopierBase<false, false, ResourceResponse> {
        typedef PassOwnPtr<CrossThreadResourceResponseData> Type;
        static Type copy(const ResourceResponse&);
    };

    template<typename T> struct CrossThreadCopier : public CrossThreadCopierBase<WTF::IsConvertibleToInteger<T>::value,
                                                                                 WTF::IsSubclassOfTemplate<typename WTF::RemoveTemplate<T, RefPtr>::Type, ThreadSafeRefCounted>::value
                                                                                     || WTF::IsSubclassOfTemplate<typename WTF::RemovePointer<T>::Type, ThreadSafeRefCounted>::value
                                                                                     || WTF::IsSubclassOfTemplate<typename WTF::RemoveTemplate<T, PassRefPtr>::Type, ThreadSafeRefCounted>::value,
                                                                                 T> {
    };

    template<typename T> struct AllowCrossThreadAccessWrapper {
    public:
        explicit AllowCrossThreadAccessWrapper(T* value) : m_value(value) { }
        T* value() const { return m_value; }
    private:
        T* m_value;
    };

    template<typename T> struct CrossThreadCopierBase<false, false, AllowCrossThreadAccessWrapper<T> > {
        typedef T* Type;
        static Type copy(const AllowCrossThreadAccessWrapper<T>& wrapper) { return wrapper.value(); }
    };

    template<typename T> AllowCrossThreadAccessWrapper<T> AllowCrossThreadAccess(T* value) 
    {
        return AllowCrossThreadAccessWrapper<T>(value);
    }

    // FIXME: Move to a different header file. AllowAccessLater is for cross-thread access
    // that is not cross-thread (tasks posted to a queue guaranteed to run on the same thread).
    template<typename T> struct AllowAccessLaterWrapper {
    public:
        explicit AllowAccessLaterWrapper(T* value) : m_value(value) { }
        T* value() const { return m_value; }
    private:
        T* m_value;
    };

    template<typename T> struct CrossThreadCopierBase<false, false, AllowAccessLaterWrapper<T> > {
        typedef T* Type;
        static Type copy(const AllowAccessLaterWrapper<T>& wrapper) { return wrapper.value(); }
    };

    template<typename T> AllowAccessLaterWrapper<T> AllowAccessLater(T* value)
    {
        return AllowAccessLaterWrapper<T>(value);
    }


} // namespace WebCore

#endif // CrossThreadCopier_h