request_queue_impl_qwqr.hpp

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/***************************************************************************
 *  foxxll/io/request_queue_impl_qwqr.hpp
 *
 *  Part of FOXXLL. See http://foxxll.org
 *
 *  Copyright (C) 2002 Roman Dementiev <[email protected]>
 *  Copyright (C) 2008, 2009 Andreas Beckmann <[email protected]>
 *  Copyright (C) 2009 Johannes Singler <[email protected]>
 *  Copyright (C) 2013 Timo Bingmann <[email protected]>
 *
 *  Distributed under the Boost Software License, Version 1.0.
 *  (See accompanying file LICENSE_1_0.txt or copy at
 *  http://www.boost.org/LICENSE_1_0.txt)
 **************************************************************************/

#ifndef FOXXLL_IO_REQUEST_QUEUE_IMPL_QWQR_HEADER
#define FOXXLL_IO_REQUEST_QUEUE_IMPL_QWQR_HEADER

#include <list>
#include <mutex>

#include <tlx/unused.hpp>

#include <foxxll/io/request_queue_impl_worker.hpp>

namespace foxxll {

//! \addtogroup foxxll_reqlayer
//! \{

//! Implementation of a local request queue having two queues, one for read and
//! one for write requests, thus having two threads. This is the default
//! implementation.
class request_queue_impl_qwqr final : public request_queue_impl_worker
{
    constexpr static bool debug = false;

private:
    using self = request_queue_impl_qwqr;
    using queue_type = std::list<request_ptr>;

    std::mutex write_mutex_;
    std::mutex read_mutex_;
    queue_type write_queue_;
    queue_type read_queue_;

    shared_state<thread_state> thread_state_;
    std::thread thread_;
    tlx::semaphore sem_;

    static const priority_op priority_op_ = WRITE;

    static void * worker(void* arg);

public:
    // \param n max number of requests simultaneously submitted to disk
    explicit request_queue_impl_qwqr(int n = 1);

    // in a multi-threaded setup this does not work as intended
    // also there were race conditions possible
    // and actually an old value was never restored once a new one was set ...
    // so just disable it and all it's nice implications
    void set_priority_op(const priority_op& op) final;
    void add_request(request_ptr& req) final;
    bool cancel_request(request_ptr& req) final;
    ~request_queue_impl_qwqr();
};

//! \}

} // namespace foxxll

#endif // !FOXXLL_IO_REQUEST_QUEUE_IMPL_QWQR_HEADER

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