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lib/Alvis/Pipeline/Read.pm  view on Meta::CPAN

	or die "can't create new file '$filename': $!";
    binmode $f2, ":utf8";
    $f2->print($doc) or die "can't write '$filename': $!";
    $f2->close() or die "can't close '$filename': $!";

    $this->_write_and_unlock($dir, $fh, $lastread, $lastwrite);
}


# A sequence file called "seq" is maintained in the spool directory,
# and is always locked when read and rewritten.  The invariant it
# preserves between lock-read-write operations is that it contains two
# numbers, space-serarate, followed by a newline.  The first number is
# that of the last document read from the spool directory.  The second
# number is that of the last document written to the spool directory,
# or zero if no document has yet been written.  If the two numbers are
# equal, there are no documents available to be read.
#
# _lock_and_read() and _write_and_unlock() together implement safe
# maintenance of the sequence file.  The former returns a filehandle,
# locked; it is the caller's responsibility to unlock the returned
# filehandle using _write_and_unlock(), like this:
#	($fh, $lastread, $lastwrite) = $this->_lock_and_read($dir);
#	# Do some stuff
#	$this->_write_and_unlock($dir, $fh, $lastread, $lastwrite);
#
sub _lock_and_read {
    my $this = shift();
    my($dir) = @_;

    my $seqfile = "$dir/seq";