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Mojo::IOLoop::ReadWriteProcess(3pm) User Contributed Perl Documentation Mojo::IOLoop::ReadWriteProcess(3pm)

NAME

Mojo::IOLoop::ReadWriteProcess - Execute external programs or internal code blocks as separate process.

SYNOPSIS

    use Mojo::IOLoop::ReadWriteProcess;
    # Code fork
    my $process = Mojo::IOLoop::ReadWriteProcess->new(sub { print "Hello\n" });
    $process->start();
    print "Running\n" if $process->is_running();
    $process->getline(); # Will return "Hello\n"
    $process->pid(); # Process id
    $process->stop();
    $process->wait_stop(); # if you intend to wait its lifespan
    # Methods can be chained, thus this is valid:
    use Mojo::IOLoop::ReadWriteProcess qw(process);
    my $output = process( sub { print "Hello\n" } )->start()->wait_stop->getline;
    # Handles seamelessy also external processes:
    my $process = process(execute=> '/path/to/bin' )->args([qw(foo bar baz)]);
    $process->start();
    my $line_output = $process->getline();
    my $pid = $process->pid();
    $process->stop();
    my @errors = $process->error;
    # Get process return value
    $process = process( sub { return "256"; } )->start()->wait_stop;
    # We need to stop it to retrieve the exit status
    my $return = $process->return_status;
    # We can access directly to handlers from the object:
    my $stdout = $process->read_stream;
    my $stdin = $process->write_stream;
    my $stderr = $process->error_stream;
    # So this works:
    print $stdin "foo bar\n";
    my @lines = <$stdout>;
    # There is also an alternative channel of communication (just for forked processes):
    my $channel_in = $process->channel_in; # write to the child process
    my $channel_out = $process->channel_out; # read from the child process
    $process->channel_write("PING"); # convenience function

DESCRIPTION

Mojo::IOLoop::ReadWriteProcess is yet another process manager.

EVENTS

Mojo::IOLoop::ReadWriteProcess inherits all events from Mojo::EventEmitter and can emit the following new ones.

start

 $process->on(start => sub {
   my ($process) = @_;
   $process->is_running();
 });

Emitted when the process starts.

stop

 $process->on(stop => sub {
   my ($process) = @_;
   $process->restart();
 });

Emitted when the process stops.

process_error

 $process->on(process_error => sub {
   my ($e) = @_;
   my @errors = @{$e};
 });

Emitted when the process produce errors.

process_stuck

 $process->on(process_stuck => sub {
   my ($self) = @_;
   ...
 });

Emitted when "blocking_stop" is set and all attempts for killing the process in "max_kill_attempts" have been exhausted. The event is emitted before attempting to kill it with SIGKILL and becoming blocking.

SIG_CHLD

 $process->on(SIG_CHLD => sub {
   my ($self) = @_;
   ...
 });

Emitted when we receive SIG_CHLD.

SIG_TERM

 $process->on(SIG_TERM => sub {
   my ($self) = @_;
   ...
 });

Emitted when the child forked process receives SIG_TERM, before exiting.

collected

 $process->on(collected => sub {
   my ($self) = @_;
   ...
 });

Emitted right after status collection.

collect_status

 $process->on(collect_status => sub {
   my ($self) = @_;
   ...
 });

Emitted when on child process waitpid. It is used internally to get the child process status. Note: events attached to it are wiped when process has been stopped.

ATTRIBUTES

Mojo::IOLoop::ReadWriteProcess inherits all attributes from Mojo::EventEmitter and implements the following new ones.

execute

    use Mojo::IOLoop::ReadWriteProcess;
    my $process = Mojo::IOLoop::ReadWriteProcess->new(execute => "/usr/bin/perl");
    $process->start();
    $process->on( stop => sub { print "Process: ".(+shift()->pid)." finished"; } );
    $process->stop();

"execute" should contain the external program that you wish to run.

code

    use Mojo::IOLoop::ReadWriteProcess;
    my $process = Mojo::IOLoop::ReadWriteProcess->new(code => sub { print "Hello" } );
    $process->start();
    $process->on( stop => sub { print "Process: ".(+shift()->pid)." finished"; } );
    $process->stop();

It represent the code you want to run in background.

You do not need to specify "code", it is implied if no arguments is given.

    my $process = Mojo::IOLoop::ReadWriteProcess->new(sub { print "Hello" });
    $process->start();
    $process->on( stop => sub { print "Process: ".(+shift()->pid)." finished"; } );
    $process->stop();

args

    use Mojo::IOLoop::ReadWriteProcess;
    my $process = Mojo::IOLoop::ReadWriteProcess->new(code => sub { print "Hello ".$_[1] }, args => "User" );
    $process->start();
    $process->on( stop => sub { print "Process: ".(+shift()->pid)." finished"; } );
    $process->stop();
    # The process will print "Hello User"

Arguments pass to the external binary or the code block. Use arrayref to pass many.

blocking_stop

    use Mojo::IOLoop::ReadWriteProcess;
    my $process = Mojo::IOLoop::ReadWriteProcess->new(code => sub { print "Hello" }, blocking_stop => 1 );
    $process->start();
    $process->on( stop => sub { print "Process: ".(+shift()->pid)." finished"; } );
    $process->stop(); # Will wait indefinitely until the process is stopped

Set it to 1 if you want to do blocking stop of the process.

channels

    use Mojo::IOLoop::ReadWriteProcess;
    my $process = Mojo::IOLoop::ReadWriteProcess->new(code => sub { print "Hello" }, channels => 0 );
    $process->start();
    $process->on( stop => sub { print "Process: ".(+shift()->pid)." finished"; } );
    $process->stop(); # Will wait indefinitely until the process is stopped

Set it to 0 if you want to disable internal channels.

session

    use Mojo::IOLoop::ReadWriteProcess;
    my $process = Mojo::IOLoop::ReadWriteProcess->new(sub { print "Hello" });
    my $session = $process->session;
    $session->enable_subreaper;

Returns the current Mojo::IOLoop::ReadWriteProcess::Session singleton.

subreaper

    use Mojo::IOLoop::ReadWriteProcess;
    my $process = Mojo::IOLoop::ReadWriteProcess->new(code => sub { print "Hello ".$_[1] }, args => "User" );
    $process->subreaper(1)->start();
    $process->on( stop => sub { shift()->disable_subreaper } );
    $process->stop();
    # The process will print "Hello User"

Mark the current process (not the child) as subreaper on start. It's on invoker behalf to disable subreaper when process stops, as it marks the current process and not the child.

ioloop

  my $loop    = $process->ioloop;
  $subprocess = $process->ioloop(Mojo::IOLoop->new);

Event loop object to control, defaults to the global Mojo::IOLoop singleton.

max_kill_attempts

    use Mojo::IOLoop::ReadWriteProcess;
    my $process = Mojo::IOLoop::ReadWriteProcess->new(code => sub { print "Hello" }, max_kill_attempts => 50 );
    $process->start();
    $process->on( stop => sub { print "Process: ".(+shift()->pid)." finished"; } );
    $process->stop(); # It will attempt to send SIGTERM 50 times.

Defaults to 5, is the number of attempts before bailing out.

It can be used with blocking_stop, so if the number of attempts are exhausted, a SIGKILL and waitpid will be tried at the end.

kill_whole_group

    use Mojo::IOLoop::ReadWriteProcess;
    my $process = Mojo::IOLoop::ReadWriteProcess->new(code => sub { setpgrp(0, 0); exec(...); }, kill_whole_group => 1 );
    $process->start();
    $process->send_signal(...); # Will skip the usual check whether $process->pid is running
    $process->stop();           # Kills the entire process group and waits for all processes in the group to finish

Defaults to 0, whether to send signals (e.g. to stop) to the entire process group.

This is useful when the sub process creates further sub processes and creates a new process group as shown in the example. In this case it might be useful to take care of the entire process group when stopping and wait for every process in the group to finish.

collect_status

Defaults to 1, If enabled it will automatically collect the status of the children process. Disable it in case you want to manage your process child directly, and do not want to rely on automatic collect status. If you won't overwrite your "SIGCHLD" handler, the "SIG_CHLD" event will be still emitted.

serialize

Defaults to 0, If enabled data returned from forked process will be serialized with Storable.

kill_sleeptime

Defaults to 1, it's the seconds to wait before attempting SIGKILL when blocking_stop is set to 1.

separate_err

Defaults to 1, it will create a separate channel to intercept process STDERR, otherwise it will be redirected to STDOUT.

verbose

Defaults to 1, it indicates message verbosity.

set_pipes

Defaults to 1, If enabled, additional pipes for process communication are automatically set up.

internal_pipes

Defaults to 1, If enabled, additional pipes for retreiving process return and errors are set up. Note: If you disable that, the only information provided by the process will be the exit_status.

autoflush

Defaults to 1, If enabled autoflush of handlers is enabled automatically.

error

Returns a Mojo::Collection of errors. Note: errors that can be captured only at the end of the process

METHODS

Mojo::IOLoop::ReadWriteProcess inherits all methods from Mojo::EventEmitter and implements the following new ones.

start()

    use Mojo::IOLoop::ReadWriteProcess qw(process);
    my $p = process(sub {
                          print STDERR "Boo\n"
                      } )->start;

Starts the process

stop()

    use Mojo::IOLoop::ReadWriteProcess qw(process);
    my $p = process( execute => "/path/to/bin" )->start->stop;

Stop the process. Unless you use wait_stop(), it will attempt to kill the process without waiting the process to finish. By defaults it send "SIGTERM" to the child. You can change that by defining the internal attribute "_default_kill_signal". Note, if you want to be *sure* that the process gets killed, you can enable the "blocking_stop" attribute, that will attempt to send "SIGKILL" after "max_kill_attempts" is reached.

restart()

    use Mojo::IOLoop::ReadWriteProcess qw(process);
    my $p = process( execute => "/path/to/bin" )->restart;

It restarts the process if stopped, or if already running, it stops it first.

is_running()

    use Mojo::IOLoop::ReadWriteProcess qw(process);
    my $p = process( execute => "/path/to/bin" )->start;
    $p->is_running;

Boolean, it inspect if the process is currently running or not.

exit_status()

    use Mojo::IOLoop::ReadWriteProcess qw(process);
    my $p = process( execute => "/path/to/bin" )->start;
    $p->wait_stop->exit_status;

Inspect the process exit status, it does the shifting magic, to access to the real value call _status().

return_status()

    use Mojo::IOLoop::ReadWriteProcess qw(process);
    my $p = process( sub { return 42 } )->start;
    my $s = $p->wait_stop->return_status; # 42

Inspect the codeblock return.

enable_subreaper()

    use Mojo::IOLoop::ReadWriteProcess qw(process);
    my $p = process()->enable_subreaper;

Mark the current process (not the child) as subreaper. This is used typically if you want to mark further children as subreapers inside other forks.

    my $master_p = process(
      sub {
        my $p = shift;
        $p->enable_subreaper;
        process(sub { sleep 4; exit 1 })->start();
        process(
          sub {
            sleep 4;
            process(sub { sleep 1; })->start();
          })->start();
        process(sub { sleep 4; exit 0 })->start();
        process(sub { sleep 4; die })->start();
        my $manager
          = process(sub { sleep 2 })->subreaper(1)->start();
        sleep 1 for (0 .. 10);
        $manager->stop;
        return $manager->session->all->size;
      });
    $master_p->subreaper(1);
    $master_p->on(collected => sub { $status++ });
    # On start we setup the current process as subreaper
    # So it's up on us to disable it after process is done.
    $master_p->on(stop => sub { shift()->disable_subreaper });
    $master_p->start();

disable_subreaper()

    use Mojo::IOLoop::ReadWriteProcess qw(process);
    my $p = process()->disable_subreaper;

Unset the current process (not the child) as subreaper.

prctl()

    use Mojo::IOLoop::ReadWriteProcess qw(process);
    my $p = process();
    $p->prctl($option, $arg2, $arg3, $arg4, $arg5);

Internal function to execute and wrap the prctl syscall, accepts the same arguments as prctl.

diag()

    use Mojo::IOLoop::ReadWriteProcess qw(process);
    my $p = process(sub { print "Hello\n" });
    $p->on( stop => sub { shift->diag("Done!") } );
    $p->start->wait_stop;

Internal function to print information to STDERR if verbose attribute is set or either DEBUG mode enabled. You can use it if you wish to display information on the process status.

to_ioloop()

    use Mojo::IOLoop::ReadWriteProcess qw(process);
    my $p = process(sub {  print "Hello from first process\n"; sleep 1 });
    $p->start(); # Start and sets the handlers
    my $stream = $p->to_ioloop; # Get the stream and demand to IOLoop
    my $output;
    # Hook on Mojo::IOLoop::Stream events
    $stream->on(read => sub { $output .= pop;  $p->is_running ...  });
    Mojo::IOLoop->singleton->start() unless Mojo::IOLoop->singleton->is_running;

Returns a Mojo::IOLoop::Stream object and demand the wait operation to Mojo::IOLoop. It needs "set_pipes" enabled. Default IOLoop can be overridden in ioloop().

wait()

    use Mojo::IOLoop::ReadWriteProcess qw(process);
    my $p = process(sub { print "Hello\n" })->wait;
    # ... here now you can mangle $p handlers and such

Waits until the process finishes, but does not performs cleanup operations (until stop is called).

wait_stop()

    use Mojo::IOLoop::ReadWriteProcess qw(process);
    my $p = process(sub { print "Hello\n" })->start->wait_stop;
    # $p is not running anymore, and all possible events have been granted to be emitted.

Waits until the process finishes, and perform cleanup operations.

errored()

    use Mojo::IOLoop::ReadWriteProcess qw(process);
    my $p = process(sub { die "Nooo" })->start->wait_stop;
    $p->errored; # will return "1"

Returns a boolean indicating if the process had errors or not.

write_pidfile()

    use Mojo::IOLoop::ReadWriteProcess qw(process);
    my $p = process(sub { die "Nooo" } );
    $p->pidfile("foobar");
    $p->start();
    $p->write_pidfile();

Forces writing PID of process to specified pidfile in the attributes of the object. Useful only if the process have been already started, otherwise if a pidfile it's supplied as attribute, it will be done automatically.

write_stdin()

    use Mojo::IOLoop::ReadWriteProcess qw(process);
    my $p = process(sub { my $a = <STDIN>; print STDERR "Hello my name is $a\n"; } )->start;
    $p->write_stdin("Larry");
    $p->read_stderr; # process STDERR will contain: "Hello my name is Larry\n"

Write data to process STDIN.

write_channel()

    use Mojo::IOLoop::ReadWriteProcess qw(process);
    my $p = process(sub {
                          my $self = shift;
                          my $parent_output = $self->channel_out;
                          my $parent_input  = $self->channel_in;
                          while(defined(my $line = <$parent_input>)) {
                            print $parent_output "PONG\n" if $line =~ /PING/i;
                          }
                      } )->start;
    $p->write_channel("PING");
    my $out = $p->read_channel;
    # $out is PONG
    my $child_output = $p->channel_out;
    while(defined(my $line = <$child_output>)) {
        print "Process is replying back with $line!\n";
        $p->write_channel("PING");
    }

Write data to process channel. Note, it's not STDIN, neither STDOUT, it's a complete separate channel dedicated to parent-child communication. In the parent process, you can access to the same pipes (but from the opposite direction):

    my $child_output = $self->channel_out;
    my $child_input  = $self->channel_in;

read_stdout()

    use Mojo::IOLoop::ReadWriteProcess qw(process);
    my $p = process(sub {
                          print "Boo\n"
                      } )->start;
    $p->read_stdout;

Gets a single line from process STDOUT.

read_channel()

    use Mojo::IOLoop::ReadWriteProcess qw(process);
    my $p = process(sub {
                          my $self = shift;
                          my $parent_output = $self->channel_out;
                          my $parent_input  = $self->channel_in;
                          print $parent_output "PONG\n";
                      } )->start;
    $p->read_channel;

Gets a single line from process channel.

read_stderr()

    use Mojo::IOLoop::ReadWriteProcess qw(process);
    my $p = process(sub {
                          print STDERR "Boo\n"
                      } )->start;
    $p->read_stderr;

Gets a single line from process STDERR.

read_all_stdout()

    use Mojo::IOLoop::ReadWriteProcess qw(process);
    my $p = process(sub {
                          print "Boo\n"
                      } )->start;
    $p->read_all_stdout;

Gets all the STDOUT output of the process.

read_all_channel()

    use Mojo::IOLoop::ReadWriteProcess qw(process);
    my $p = process(sub {
                          shift->channel_out->write("Ping")
                      } )->start;
    $p->read_all_channel;

Gets all the channel output of the process.

read_all_stderr()

    use Mojo::IOLoop::ReadWriteProcess qw(process);
    my $p = process(sub {
                          print STDERR "Boo\n"
                      } )->start;
    $p->read_all_stderr;

Gets all the STDERR output of the process.

send_signal()

    use Mojo::IOLoop::ReadWriteProcess qw(process);
    use POSIX;
    my $p = process( execute => "/path/to/bin" )->start;
    $p->send_signal(POSIX::SIGKILL);

Send a signal to the process

EXPORTS

parallel()

    use Mojo::IOLoop::ReadWriteProcess qw(parallel);
    my $pool = parallel sub { print "Hello\n" } => 5;
    $pool->start();
    $pool->on( stop => sub { print "Process: ".(+shift()->pid)." finished"; } );
    $pool->stop();

Returns a Mojo::IOLoop::ReadWriteProcess::Pool object that represent a group of processes.

It accepts the same arguments as Mojo::IOLoop::ReadWriteProcess, and the last one represent the number of processes to generate.

batch()

    use Mojo::IOLoop::ReadWriteProcess qw(batch);
    my $pool = batch;
    $pool->add(sub { print "Hello\n" });
    $pool->on(stop => sub { shift->_diag("Done!") })->start->wait_stop;

Returns a Mojo::IOLoop::ReadWriteProcess::Pool object generated from supplied arguments. It accepts as input the same parameter of Mojo::IOLoop::ReadWriteProcess::Pool constructor ( see parallel() ).

process()

    use Mojo::IOLoop::ReadWriteProcess qw(process);
    my $p = process sub { print "Hello\n" };
    $p->start()->wait_stop;

or even:

    process(sub { print "Hello\n" })->start->wait_stop;

Returns a Mojo::IOLoop::ReadWriteProcess object that represent a process.

It accepts the same arguments as Mojo::IOLoop::ReadWriteProcess.

queue()

    use Mojo::IOLoop::ReadWriteProcess qw(queue);
    my $q = queue;
    $q->add(sub { return 42 } );
    $q->consume;

Returns a Mojo::IOLoop::ReadWriteProcess::Queue object that represent a queue.

DEBUGGING

You can set the MOJO_EVENTEMITTER_DEBUG environment variable to get some advanced diagnostics information printed to STDERR.

    MOJO_EVENTEMITTER_DEBUG=1

Also, you can set MOJO_PROCESS_DEBUG environment variable to get diagnostics about the process execution.

    MOJO_PROCESS_DEBUG=1

LICENSE

Copyright (C) Ettore Di Giacinto.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

AUTHOR

Ettore Di Giacinto <edigiacinto@suse.com>

2024-03-08 perl v5.40.0