wbtl_file.h

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/***************************************************************************
 * include/stxxl/bits/io/wbtl_file.h
 *
 * a write-buffered-translation-layer pseudo file
 *
 * Part of the STXXL. See http://stxxl.sourceforge.net
 *
 * Copyright (C) 2008-2009 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_WBTL_FILE_HEADER
#define STXXL_IO_WBTL_FILE_HEADER

#ifndef STXXL_HAVE_WBTL_FILE
#define STXXL_HAVE_WBTL_FILE 1
#endif

#if STXXL_HAVE_WBTL_FILE

#include <map>

#include <stxxl/bits/io/disk_queued_file.h>


STXXL_BEGIN_NAMESPACE

//! \addtogroup fileimpl
//! \{

//! Implementation of file based on buffered writes and block remapping via a
//! translation layer.
class wbtl_file : public disk_queued_file
{
 typedef std::pair<offset_type, offset_type> place;
 typedef std::map<offset_type, offset_type> sortseq;
 typedef std::map<offset_type, place> place_map;

 // the physical disk used as backend
 file* storage;
 offset_type sz;
 size_type write_block_size;

 mutex mapping_mutex;
 // logical to physical address translation
 sortseq address_mapping;
 // physical to (logical address, size) translation
 place_map reverse_mapping;
 // list of free (physical) regions
 sortseq free_space;
 offset_type free_bytes;

 // the write buffers:
 // write_buffer[curbuf] is the current write buffer
 // write_buffer[1-curbuf] is the previous write buffer
 // buffer_address if the start offset on the backend file
 // curpos is the next writing position in write_buffer[curbuf]
 mutex buffer_mutex;
 char* write_buffer[2];
 offset_type buffer_address[2];
 int curbuf;
 size_type curpos;
 request_ptr backend_request;

 struct FirstFit : public std::binary_function<place, offset_type, bool>
 {
 bool operator () (
 const place& entry,
 const offset_type size) const
 {
 return (entry.second >= size);
 }
 };

public:
 //! Constructs file object.
 //! param backend_file file object used as storage backend, will be deleted in ~wbtl_file()
 wbtl_file(
 file* backend_file,
 size_type write_buffer_size,
 int write_buffers = 2,
 int queue_id = DEFAULT_QUEUE,
 int allocator_id = NO_ALLOCATOR);
 ~wbtl_file();
 offset_type size();
 void set_size(offset_type newsize);
 void lock();
 void serve(const request* req) throw (io_error);
 void discard(offset_type offset, offset_type size);
 const char * io_type() const;

private:
 void _add_free_region(offset_type offset, offset_type size);

protected:
 void sread(void* buffer, offset_type offset, size_type bytes);
 void swrite(void* buffer, offset_type offset, size_type bytes);
 offset_type get_next_write_block();
 void check_corruption(offset_type region_pos, offset_type region_size,
 sortseq::iterator pred, sortseq::iterator succ);
};

//! \}

STXXL_END_NAMESPACE

#endif // #if STXXL_HAVE_WBTL_FILE

#endif // !STXXL_IO_WBTL_FILE_HEADER