IO::Lambda::Flock - lambda-style file locking

IO-Lambda documentation Contained in the IO-Lambda distribution.

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NAME

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IO::Lambda::Flock - lambda-style file locking

DESCRIPTION

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The module provides file locking interface for the lambda style, implemented by using non-blocking, periodic polling of flock(2).

SYNOPSIS

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    open LOCK, ">lock";
    lambda {
        # obtain the lock 
        context \*LOCK, timeout => 10;
        flock { die "can't obtain lock" unless shift }

        # while reading from handle
        context $handle;
        readable { ... }

        # and showing status 
        context 0.5;
        timeout { print '.'; again }
    };

API

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flock($filehandle, %options) -> ($lock_obtained = 1 | $timeout = 0)

Waits until the file lock is obtained or the timeout is expired. When successful, the (shared or exclusive) lock on $filehandle is acquired by flock($filehandle, LOCK_NB) call. Options:

timeout or deadline

These two options are synonyms, both declare the moment when the lambda waiting for the lock should give up. If undef, timeout never occurs.

shared

If set, LOCK_SH is used, otherwise LOCK_EX.

frequency

Defines how often the polling for the lock should occur. If left undefined, polling occurs during idle time, when other events are dispatched.

SEE ALSO

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Fcntl, IO::Lambda::Poll.

AUTHOR

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Dmitry Karasik, <dmitry@karasik.eu.org>.

IO-Lambda documentation Contained in the IO-Lambda distribution. 
# $Id: Flock.pm,v 1.8 2009/04/21 14:42:46 dk Exp $
package IO::Lambda::Flock;
use vars qw($DEBUG @ISA @EXPORT_OK);
@ISA = qw(Exporter);
@EXPORT_OK   = qw(flock);
%EXPORT_TAGS = ( all => \@EXPORT_OK);
$DEBUG = $IO::Lambda::DEBUG{flock} || 0;

use strict;
use warnings;
use Fcntl ':flock';
use IO::Lambda qw(:all :dev);
use IO::Lambda::Poll qw(poll_event);

sub poll_flock
{
	my ( $expired, $fh, $shared) = @_;
	if ( CORE::flock( $fh, LOCK_NB | ($shared ? LOCK_SH : LOCK_EX) )) {
		warn "flock $fh obtained\n" if $DEBUG;
		return 1, 1;
	}
	return 1, 0 if $expired;
	return 0;
}

sub flock(&)
{
	return this-> override_handler('flock', \&flock, shift)
		if this-> {override}->{flock};

	my $cb = _subname flock => shift;
	my ($fh, %opt) = context;
	my $deadline = exists($opt{timeout}) ? $opt{timeout} : $opt{deadline};

	poll_event(
		$cb, \&flock, \&poll_flock, 
		$deadline, $opt{frequency}, 
		$fh, $opt{shared}
	);
}


# The same code can be written way more elegant:
#
#	sub flock(&)
#	{
#		poller { 
#			my %opt = @_;
#			CORE::flock( 
#				$opt{fh}, 
#				LOCK_NB | ($opt{shared} ? LOCK_SH : LOCK_EX
#			);
#		}
#		-> call(context)
#		-> condition(shift, \&flock, 'flock')
#	}
#
#  but will require another calling style:
#
#	context fh => $fh, deadline => 5;
#	flock { ok }

1;

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