request_queue_impl_qwqr.h

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/***************************************************************************
 *  include/stxxl/bits/io/request_queue_impl_qwqr.h
 *
 *  Part of the STXXL. See http://stxxl.sourceforge.net
 *
 *  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 STXXL_IO_REQUEST_QUEUE_IMPL_QWQR_HEADER
#define STXXL_IO_REQUEST_QUEUE_IMPL_QWQR_HEADER

#include <list>

#include <stxxl/bits/io/request_queue_impl_worker.h>
#include <stxxl/bits/common/mutex.h>

STXXL_BEGIN_NAMESPACE

//! \addtogroup 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 : public request_queue_impl_worker
{
private:
    typedef request_queue_impl_qwqr self;
    typedef std::list<request_ptr> queue_type;

    mutex m_write_mutex;
    mutex m_read_mutex;
    queue_type m_write_queue;
    queue_type m_read_queue;

    state<thread_state> m_thread_state;
    thread_type m_thread;
    semaphore m_sem;

    static const priority_op m_priority_op = WRITE;

    static void * worker(void* arg);

public:
    // \param n max number of requests simultaneously submitted to disk
    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(priority_op op)
    {
        //_priority_op = op;
        STXXL_UNUSED(op);
    }
    void add_request(request_ptr& req);
    bool cancel_request(request_ptr& req);
    ~request_queue_impl_qwqr();
};

//! \}

STXXL_END_NAMESPACE

#endif // !STXXL_IO_REQUEST_QUEUE_IMPL_QWQR_HEADER
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