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".

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() == -1 and 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.
     } }
 }