package Proc::Fork;
{
$Proc::Fork::VERSION = '0.802';
}
use strict;
use warnings;
# ABSTRACT: simple, intuitive interface to the fork() system call
use Exporter::Tidy (
default => [ ':all' ],
wrapper => [ 'run_fork' ],
blocks => [ qw( parent child error retry ) ],
);
sub _croak { require Carp; goto &Carp::croak }
my $do_clear = 1;
my ( $parent, $child, $error, $retry );
sub run_fork(&) {
my $setup = shift;
my @r = $setup->();
_croak "Garbage in Proc::Fork setup (semicolon after last block clause?)" if @r;
$do_clear = 1;
my $pid;
my $i;
{
$pid = fork;
last if defined $pid;
redo if $retry and $retry->( ++$i );
die "Cannot fork: $!\n" if not $error;
$error->();
return;
}
$_->( $pid || () ) for ( $pid ? $parent : $child ) || ();
return;
}
for my $block ( qw( parent child error retry ) ) {
my $code = q{sub _BLOCK_ (&;@) {
$parent = $child = $error = $retry = $do_clear = undef if $do_clear;
_croak "Duplicate _BLOCK_ clause in Proc::Fork setup" if $_BLOCK_;
$_BLOCK_ = shift if 'CODE' eq ref $_[0];
_croak "Garbage in Proc::Fork setup (after _BLOCK_ clause)" if @_;
run_fork {} if not defined wantarray; # backcompat
();
}};
$code =~ s/_BLOCK_/$block/g;
eval $code;
}
1;
__END__
=pod
=head1 NAME
Proc::Fork - simple, intuitive interface to the fork() system call
=head1 VERSION
version 0.802
=head1 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)
}
};
=head1 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.
=head1 INTERFACE
=head2 run_fork
run_fork { ... }
Performs the fork operation configured in its block.
=head2 child
child { ... }
Declares the block that should run in the child process.
=head2 parent
parent { ... }
Declares the block that should run in the parent process. The child's PID is passed as an argument to the block.
=head2 retry
retry { ... }
Declares the block that should run in case of an error, ie. if C<fork> returned C<undef>. If the code returns true, another C<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 C<retry> clause is not used, no retries will be attempted and a fork failure will immediately lead to the C<error> clause being called.
=head2 error
error { ... }
Declares the block that should run if there was an error, ie when C<fork> returns C<undef> and the C<retry> clause returns false. The number of forks attempted is passed as an argument to the block.
If an C<error> clause is not used, errors will raise an exception using C<die>.
=head1 EXAMPLES
=head2 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";
}
};
=head2 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";
}
=head2 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
=head2 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.
} }
}
=head1 EXPORTS
This package exports the following symbols by default.
=over 4
=item * C<run_fork>
=item * C<child>
=item * C<parent>
=item * C<retry>
=item * C<error>
=back
=head1 BUGS AND LIMITATIONS
None currently known, for what that's worth.
Please report bugs or feature requests to L<http://github.com/ap/Proc-Fork/issues>.
=head1 AUTHOR
Aristotle Pagaltzis <pagaltzis@gmx.de>
Documentation by Eric J. Roode.
=head1 COPYRIGHT AND LICENSE
This software is copyright (c) 2013 by Aristotle Pagaltzis.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.
=cut