NAME

 Genezzo::BufCa::BCFile.pm - A simple in-memory buffer cache for 
 multiple files for a single process, without locking.

SYNOPSIS

 use Genezzo::BufCa::BCFile;
 
 # get a buffer cache
 my $bc = Genezzo::BufCa::BCFile->new(blocksize => 10, numblocks => 5);
 # register a file
 my $fileno = Genezzo::BufCa::BCFile->FileReg(FileName => 'file.dat');
 # get back some block 
 $bceref = $bc->ReadBlock(filenum  => $fileno,
                          blocknum => $blocknum);
 $bce = $$bceref;

DESCRIPTION

 The file buffer cache is a simple module designed to form the
 basis of a more complicated multi-process buffer cache
 with locking.  The buffer cache contains a number of Buffer Cache
 Elements (BCEs), a special wrapper class for simple byte buffers
 (blocks).  See L<Genezzo::BufCa::BufCa>.
 Note that this module does not perform space management or allocation 
 within the files -- it only reads and writes the blocks.  The caller
 is responsible for managing the contents of the file.

FUNCTIONS

new

 Takes arguments blocksize (required, in bytes), numblocks (10 by
 default).  Returns a new buffer cache of the specified number of
 blocks of size blocksize.

BCFileInfoByName Return the file state information.

FileSetHeaderInfoByName Update the datafile header.

FileReg

 Register a file with the cache -- returns a file number.  Reregistering
 a file should return the same number.

ReadBlock

 Takes argument blocknum, which must be a valid block number, and
 the argument filenum, which must be a valid file number.  If the
 block is in memory it returns the bceref.  If the block is not in
 the cache it fetches it from disk into an unused block.  If the 
 unused block is dirty, then ReadBlock writes it out first.  
 Fails if all blocks are in use.

WriteBlock

 Write a block to disk.  Not really necessary -- ReadBlock will
 flush some dirty blocks to disk automatically, and Flush
 will write all dirty blocks to disk.

Flush

 Write all dirty blocks to disk.

Rollback

 Discard all dirty blocks and replace with blocks from disk..

EXPORT

 None by default.

LIMITATIONS

Currently requires 2 blocks per open file.

TODO

note that _fileread could just be part of GetContrib
need to move TSExtendFile functionality here if want to overload syswrite with encryption
read_only database support
buffer cache block zero should contain description of buffer cache layout
need a way to free blocks associated with a file that is not currently in use

AUTHOR

 Jeffrey I. Cohen, jcohen@genezzo.com

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    any later version.
    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.
    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

Address bug reports and comments to: jcohen@genezzo.com

For more information, please visit the Genezzo homepage at <http://www.genezzo.com>