NAME

IO::Async::ChildManager - facilitates the execution of child processes

SYNOPSIS

Usually this object would be used indirectly, via an IO::Async::Loop:

 use IO::Async::Loop::...;
 my $loop = IO::Async::Loop::...

 $loop->enable_childmanager;

 ...

 $loop->watch_child( 1234 => sub { print "Child 1234 exited\n" } );

 $loop->spawn_child(
    command => "/usr/bin/something",
    on_exit => \&exit_handler,
    setup => [
       stdout => $pipe,
    ]
 );

DESCRIPTION

This module provides a class that manages the execution of child processes. It acts as a central point to store PID values of currently-running children, and to call the appropriate callback handler code when the process terminates.

Callbacks

When the waitpid() call returns a PID that the manager is observing, the registered callback function is invoked with its PID and the current value of the $? variable.

 $code->( $pid, $? )

After invocation, the handler is automatically removed from the manager.

CONSTRUCTOR

$manager = IO::Async::ChildManager->new( %params )

This function returns a new instance of a IO::Async::ChildManager object. The %params hash takes the following keys:

loop => IO::Async::Loop

A reference to an IO::Async::Loop object.

METHODS

$manager->watch( $kid, $code )

This method adds a new handler for the termination of the given child PID.

$kid

The PID to watch.

$code

A CODE reference to the handling function.

$watching = $manager->is_watching( $kid )

This method tests if the manager is currently watching for termination of the given PID. It returns a boolean value.

$kid

The PID.

@kids = $manager->list_watching()

This method returns a list of the PIDs that the manager is currently watching for. The list is returned in no particular order.

$pid = $manager->detach_child( %params )

This method creates a new child process to run a given code block.

code => CODE

A block of code to execute in the child process. It will be called in scalar context inside an eval block. The return value will be used as the exit() code from the child if it returns (or 255 if it returned undef or thows an exception).

on_exit => CODE

A optional callback function to be called when the child processes exits. It will be invoked in the following way:

 $on_exit->( $pid, $exitcode )

This key is optional; if not supplied, the calling code should install a handler using the watch_child() method.

keep_signals => BOOL

Optional boolean. If missing or false, any CODE references in the %SIG hash will be removed and restored back to DEFAULT in the child process. If true, no adjustment of the %SIG hash will be performed.

$pid = $manager->spawn( %params )

This method creates a new child process to run a given code block or command. The %params hash takes the following keys:

command => ARRAY or STRING

Either a reference to an array containing the command and its arguments, or a plain string containing the command. This value is passed into perl's exec() function.

code => CODE

A block of code to execute in the child process. It will be called in scalar context inside an eval block.

setup => ARRAY

A reference to an array which gives file descriptors to set up in the child process before running the code or command. See below.

on_exit => CODE

A callback function to be called when the child processes exits. It will be invoked in the following way:

 $on_exit->( $pid, $exitcode, $dollarbang, $dollarat )

Exactly one of the command or code keys must be specified.

If the command key is used, the given array or string is executed using the exec() function.

If the code key is used, the return value will be used as the exit() code from the child if it returns (or 255 if it returned undef or thows an exception).

 Case            | WEXITSTATUS($exitcode) | $dollarbang | $dollarat
 ----------------+------------------------+-------------+----------
 exec() succeeds | exit code from program |     0       |    ""
 exec() fails    |         255            |     $!      |    ""
 $code returns   |     return value       |     $!      |    ""
 $code dies      |         255            |     $!      |    $@

It is usually more convenient to use the open() method in simple cases where an external program is being started in order to interact with it via file IO.

setup array

This array gives a list of file descriptor operations to perform in the child process after it has been fork()ed from the parent, before running the code or command. It consists of name/value pairs which are ordered; the operations are performed in the order given.

fdn => ARRAY

Gives an operation on file descriptor n. The first element of the array defines the operation to be performed:

[ 'close' ]

The file descriptor will be closed.

[ 'dup', $io ]

The file descriptor will be dup2()ed from the given IO handle.

[ 'open', $mode, $file ]

The file descriptor will be opened from the named file in the given mode. The $mode string should be in the form usually given to the open() function; such as '<' or '>>'.

fdn => IO

A shortcut for the dup case given above.

stdin => ...

stdout => ...

stderr => ...

Shortcuts for fd0, fd1 and fd2 respectively.

env => HASH

A reference to a hash to set as the child process's environment.

$pid = $manager->open( %params )

This creates a new child process to run the given code block or command, and attaches filehandles to it that the parent will watch. The %params hash takes the following keys:

command => ARRAY or STRING

code => CODE

The command or code to run in the child process (as per the spawn method)

on_finish => CODE

A callback function to be called when the child process exits and has closed all of the filehandles that were set up for it. It will be invoked in the following way:

 $on_finish->( $pid, $exitcode )

on_error => CODE

Optional callback to be called when the child code block throws an exception, or the command could not be exec()ed. It will be invoked in the following way (as per spawn)

 $on_error->( $pid, $exitcode, $dollarbang, $dollarat )

If this callback is not supplied, then on_finish is used instead. The value of $! and $@ will not be reported.

setup => ARRAY

Optional reference to an array to pass to the underlying spawn method.

In addition, the hash takes keys that define how to set up file descriptors in the child process. (If the setup array is also given, these operations will be performed after those specified by setup.)

fdn => HASH

A hash describing how to set up file descriptor n. The hash may contain one of the following sets of keys:

on_read => CODE

The child will be given the writing end of a pipe. The reading end will be wrapped by an IO::Async::Stream using this on_read callback function.

from => STRING

The child will be given the reading end of a pipe. The string given by the from parameter will be written to the child. When all of the data has been written the pipe will be closed.

stdin => ...

stdout => ...

stderr => ...

Shortcuts for fd0, fd1 and fd2 respectively.

$pid = $manager->run( %params )

This creates a new child process to run the given code block or command, capturing its STDOUT and STDERR streams. When the process exits, the callback is invoked being passed the exitcode, and content of the streams.

command => ARRAY or STRING

code => CODE

The command or code to run in the child process (as per the spawn method)

on_finish => CODE

A callback function to be called when the child process exits and closed its STDOUT and STDERR streams. It will be invoked in the following way:

 $on_finish->( $pid, $exitcode, $stdout, $stderr )

stdin => STRING

Optional. String to pass in to the child process's STDIN stream.

This function is intended mainly as an IO::Async-compatible replacement for the perl readpipe function (`backticks`), allowing it to replace

  my $output = `command here`;

with

 $loop->run(
    command => "command here", 
    on_finish => sub {
       my ( undef, $exitcode, $output ) = @_;
       ...
    }
 );

AUTHOR

Paul Evans <leonerd@leonerd.org.uk>