dyn_block_reader.hpp

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/*******************************************************************************
 * thrill/data/dyn_block_reader.hpp
 *
 * Dynamized instantiation of BlockReader which can polymorphically read from
 * different block sources using the same object type.
 *
 * Part of Project Thrill - http://project-thrill.org
 *
 * Copyright (C) 2015 Timo Bingmann <[email protected]>
 *
 * All rights reserved. Published under the BSD-2 license in the LICENSE file.
 ******************************************************************************/

#pragma once
#ifndef THRILL_DATA_DYN_BLOCK_READER_HEADER
#define THRILL_DATA_DYN_BLOCK_READER_HEADER

#include <thrill/data/block_reader.hpp>

namespace thrill {
namespace data {

//! \addtogroup data_layer
//! \{

/*!
 * This is a pure virtual base which will be used to fetch Blocks for the
 * BlockReader from different sources.
 */
class DynBlockSourceInterface : public tlx::ReferenceCounter
{
public:
    virtual ~DynBlockSourceInterface() { }

    virtual PinnedBlock NextBlock() = 0;

    //! set number of blocks to prefetch
    virtual void Prefetch(size_t size) = 0;
};

/*!
 * This is the actual BlockSource used to instantiate BlockReader. The
 * BlockSource holds a shared pointer to the polymorphic block source, which is
 * derived from the above virtual base class.
 *
 * Think of this class being embedded into the BlockReader and delivering Blocks
 * via the virtual function class from whatever is attached.
 */
class DynBlockSource
{
public:
    DynBlockSource() { }

    explicit DynBlockSource(
        tlx::CountingPtr<DynBlockSourceInterface>&& block_source_ptr)
        : block_source_ptr_(std::move(block_source_ptr)) { }

    PinnedBlock NextBlock() {
        return block_source_ptr_->NextBlock();
    }

    void Prefetch(size_t size) {
        return block_source_ptr_->Prefetch(size);
    }

private:
    tlx::CountingPtr<DynBlockSourceInterface> block_source_ptr_;
};

//! Instantiation of BlockReader for reading from the polymorphic source.
using DynBlockReader = BlockReader<DynBlockSource>;

/*!
 * Adapter class to wrap any existing BlockSource concept class into a
 * DynBlockSourceInterface.
 */
template <typename BlockSource>
class DynBlockSourceAdapter final : public DynBlockSourceInterface
{
public:
    explicit DynBlockSourceAdapter(BlockSource&& block_source)
        : block_source_(std::move(block_source)) { }

    //! non-copyable: delete copy-constructor
    DynBlockSourceAdapter(const DynBlockSourceAdapter&) = delete;
    //! non-copyable: delete assignment operator
    DynBlockSourceAdapter& operator = (const DynBlockSourceAdapter&) = delete;
    //! move-constructor: default
    DynBlockSourceAdapter(DynBlockSourceAdapter&&) = default;
    //! move-assignment operator: default
    DynBlockSourceAdapter& operator = (DynBlockSourceAdapter&&) = default;

    PinnedBlock NextBlock() final {
        return block_source_.NextBlock();
    }

    void Prefetch(size_t size) final {
        return block_source_.Prefetch(size);
    }

private:
    BlockSource block_source_;
};

/*!
 * Method to construct a DynBlockSource from a non-polymorphic BlockSource. The
 * variadic parameters are passed to the constructor of the existing
 * BlockSource.
 */
template <typename BlockSource, typename... Params>
DynBlockSource ConstructDynBlockSource(Params&& ... params) {
    return DynBlockSource(
        tlx::make_counting<DynBlockSourceAdapter<BlockSource> >(
            BlockSource(std::forward<Params>(params) ...)));
}

/*!
 * Method to construct a DynBlockReader from a non-polymorphic BlockSource. The
 * variadic parameters are passed to the constructor of the existing
 * BlockSource.
 */
template <typename BlockSource, typename... Params>
DynBlockReader ConstructDynBlockReader(Params&& ... params) {
    return DynBlockReader(
        ConstructDynBlockSource<BlockSource>(std::forward<Params>(params) ...));
}

//! \}

} // namespace data
} // namespace thrill

#endif // !THRILL_DATA_DYN_BLOCK_READER_HEADER

/******************************************************************************/