disk_queues.h

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/***************************************************************************
 * include/stxxl/bits/io/disk_queues.h
 *
 * Part of the STXXL. See http://stxxl.sourceforge.net
 *
 * Copyright (C) 2002 Roman Dementiev <[email protected]>
 * Copyright (C) 2008-2010 Andreas Beckmann <[email protected]>
 * Copyright (C) 2009 Johannes Singler <[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_DISK_QUEUES_HEADER
#define STXXL_IO_DISK_QUEUES_HEADER

#include <map>

#include <stxxl/bits/namespace.h>
#include <stxxl/bits/singleton.h>
#include <stxxl/bits/io/iostats.h>
#include <stxxl/bits/io/request.h>
#include <stxxl/bits/io/request_queue_impl_qwqr.h>


STXXL_BEGIN_NAMESPACE

//! \addtogroup iolayer
//! \{

//! Encapsulates disk queues.
//! \remark is a singleton
class disk_queues : public singleton<disk_queues>
{
 friend class singleton<disk_queues>;

 // 2 queues: write queue and read queue
 typedef request_queue_impl_qwqr request_queue_type;

 typedef stxxl::int64 DISKID;
 typedef std::map<DISKID, request_queue_type*> request_queue_map;

protected:
 request_queue_map queues;
 disk_queues()
 {
 stxxl::stats::get_instance(); // initialize stats before ourselves
 }

public:
 void add_request(request_ptr& req, DISKID disk)
 {
#ifdef STXXL_HACK_SINGLE_IO_THREAD
 disk = 42;
#endif
 if (queues.find(disk) == queues.end())
 {
 // create new request queue
 queues[disk] = new request_queue_type();
 }
 queues[disk]->add_request(req);
 }

 //! Cancel a request.
 //! The specified request is canceled unless already being processed.
 //! However, cancelation cannot be guaranteed.
 //! Cancelled requests must still be waited for in order to ensure correct
 //! operation.
 //! \param req request to cancel
 //! \param disk disk number for disk that \c req was scheduled on
 //! \return \c true iff the request was canceled successfully
 bool cancel_request(request_ptr& req, DISKID disk)
 {
#ifdef STXXL_HACK_SINGLE_IO_THREAD
 disk = 42;
#endif
 if (queues.find(disk) != queues.end())
 return queues[disk]->cancel_request(req);
 else
 return false;
 }

 ~disk_queues()
 {
 // deallocate all queues
 for (request_queue_map::iterator i = queues.begin(); i != queues.end(); i++)
 delete (*i).second;
 }

 //! Changes requests priorities.
 //! \param op one of:
 //! - READ, read requests are served before write requests within a disk queue
 //! - WRITE, write requests are served before read requests within a disk queue
 //! - NONE, read and write requests are served by turns, alternately
 void set_priority_op(request_queue::priority_op op)
 {
 for (request_queue_map::iterator i = queues.begin(); i != queues.end(); i++)
 i->second->set_priority_op(op);
 }
};

//! \}

STXXL_END_NAMESPACE

#endif // !STXXL_IO_DISK_QUEUES_HEADER
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