NAME

       Proc::Fork - simple, intuitive interface to the fork() system call

VERSION

       version 0.804

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 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"

BUGS AND LIMITATIONS

       None currently known, for what that's worth.

       Please report bugs or feature requests to <http://github.com/ap/Proc-Fork/issues>.

AUTHOR

       Aristotle Pagaltzis <pagaltzis@gmx.de>

       Documentation by Eric J. Roode.

COPYRIGHT AND LICENSE

       This documentation is copyright (c) 2002 by Eric J. Roode.

       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.