NAME¶
Proc::Fork - Simple, intuitive interface to the fork() system call
VERSION¶
This documentation describes Proc::Fork version 0.71
SYNOPSIS¶
use Proc::Fork;
run_fork {
child {
# child code goes here.
}
parent {
my $child_pid = shift;
# parent code goes here.
waitpid $child_pid, 0;
}
retry {
my $attempts = shift;
# what to do if if fork() fails:
# return true to try again, false to abort
return if $attempts > 5;
sleep 1, return 1;
}
error {
# Error-handling code goes here
# (fork() failed and the retry block returned false)
}
};
DESCRIPTION¶
This module provides an intuitive, Perl-ish way to write forking programs by
letting you use blocks to illustrate which code section executes in which
fork. The code for the parent, child, retry handler and error handler are
grouped together in a "fork block". The clauses may appear in any
order, but they must be consecutive (without any other statements in between).
All four clauses need not be specified. If the retry clause is omitted, only one
fork will be attempted. If the error clause is omitted the program will die
with a simple message if it can't retry. If the parent or child clause is
omitted, the respective (parent or child) process will start execution after
the final clause. So if one or the other only has to do some simple action,
you need only specify that one. For example:
# spawn off a child process to do some simple processing
run_fork { child {
exec '/bin/ls', '-l';
die "Couldn't exec ls: $!\n";
} };
# Parent will continue execution from here
# ...
If the code in any of the clauses does not die or exit, it will continue
execution after the fork block.
INTERFACE¶
run_fork¶
run_fork { ... }
Performs the fork operation configured in its block.
child¶
child { ... }
Declares the block that should run in the child process.
parent¶
parent { ... }
Declares the block that should run in the parent process. The child's PID is
passed as an argument to the block.
retry¶
retry { ... }
Declares the block that should run in case of an error, ie. if "fork"
returned "undef". If the code returns true, another "fork"
is attempted. The number of fork attempts so far is passed as an argument to
the block.
This can be used to implement a wait-and-retry logic that may be essential for
some applications like daemons.
If a "retry" clause is not used, no retries will be attempted and a
fork failure will immediately lead to the "error" clause being
called.
error¶
error { ... }
Declares the block that should run if there was an error, ie when
"fork" returns "undef" and the "retry" clause
returns false. The number of forks attempted is passed as an argument to the
block.
If an "error" clause is not used, errors will raise an exception using
"die".
EXAMPLES¶
Simple example with IPC via pipe¶
use strict;
use Proc::Fork;
use IO::Pipe;
my $p = IO::Pipe->new;
run_fork {
parent {
my $child = shift;
$p->reader;
print while <$p>;
waitpid $child,0;
}
child {
$p->writer;
print $p "Line 1\n";
print $p "Line 2\n";
exit;
}
retry {
if( $_[0] < 5 ) {
sleep 1;
return 1;
}
return 0;
}
error {
die "That's all folks\n";
}
};
Multi-child example¶
use strict;
use Proc::Fork;
use IO::Pipe;
my $num_children = 5; # How many children we'll create
my @children; # Store connections to them
$SIG{CHLD} = 'IGNORE'; # Don't worry about reaping zombies
# Spawn off some children
for my $num ( 1 .. $num_children ) {
# Create a pipe for parent-child communication
my $pipe = IO::Pipe->new;
# Child simply echoes data it receives, until EOF
run_fork { child {
$pipe->reader;
my $data;
while ( $data = <$pipe> ) {
chomp $data;
print STDERR "child $num: [$data]\n";
}
exit;
} };
# Parent here
$pipe->writer;
push @children, $pipe;
}
# Send some data to the kids
for ( 1 .. 20 ) {
# pick a child at random
my $num = int rand $num_children;
my $child = $children[$num];
print $child "Hey there.\n";
}
Daemon example¶
use strict;
use Proc::Fork;
use POSIX;
# One-stop shopping: fork, die on error, parent process exits.
run_fork { parent { exit } };
# Other daemon initialization activities.
$SIG{INT} = $SIG{TERM} = $SIG{HUP} = $SIG{PIPE} = \&some_signal_handler;
POSIX::setsid() or die "Cannot start a new session: $!\n";
close $_ for *STDIN, *STDOUT, *STDERR;
# rest of daemon program follows
Forking socket-based network server example¶
use strict;
use IO::Socket::INET;
use Proc::Fork;
$SIG{CHLD} = 'IGNORE';
my $server = IO::Socket::INET->new(
LocalPort => 7111,
Type => SOCK_STREAM,
Reuse => 1,
Listen => 10,
) or die "Couln't start server: $!\n";
my $client;
while ($client = $server->accept) {
run_fork { child {
# Service the socket
sleep(10);
print $client "Ooga! ", time % 1000, "\n";
exit; # child exits. Parent loops to accept another connection.
} }
}
EXPORTS¶
This package exports the following symbols by default.
- •
- "run_fork"
- •
- "child"
- •
- "parent"
- •
- "retry"
- •
- "error"
DEPENDENCIES¶
Carp, which is part of the Perl distribution, and Exporter::Tidy.
BUGS AND LIMITATIONS¶
None currently known, for what that's worth.
Please report any bugs or feature requests to
"bug-proc-fork@rt.cpan.org", or through the web interface at
<
https://rt.cpan.org/NoAuth/ReportBug.html?Queue=Proc-Fork>. I will be
notified, and then you'll automatically be notified of progress on your bug as
I make changes.
AUTHOR¶
Aristotle Pagaltzis, <mailto:pagaltzis@gmx.de>
Documentation by Eric J. Roode.
COPYRIGHT AND LICENSE¶
Copyright (c) 2005-2008 by Aristotle Pagaltzis. All rights Reserved.
This module is free software; you can redistribute it and/or modify it under the
same terms as Perl itself. See perlartistic.
DISCLAIMER OF WARRANTY¶
BECAUSE THIS SOFTWARE IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE
SOFTWARE, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE
STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE
SOFTWARE "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR
IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO
THE QUALITY AND PERFORMANCE OF THE SOFTWARE IS WITH YOU. SHOULD THE SOFTWARE
PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR, OR
CORRECTION.
IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY
COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE
SOFTWARE AS PERMITTED BY THE ABOVE LICENCE, BE LIABLE TO YOU FOR DAMAGES,
INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING
OUT OF THE USE OR INABILITY TO USE THE SOFTWARE (INCLUDING BUT NOT LIMITED TO
LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR
THIRD PARTIES OR A FAILURE OF THE SOFTWARE TO OPERATE WITH ANY OTHER
SOFTWARE), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.