Mojo::IOLoop(3)

🌸 NAME 🌸

Bestie, this is Mojo::IOLoop(3), straight outta the User Contributed Perl Documentation, and it is literally a minimalistic event loop. That’s the whole name: Mojo::IOLoop — Minimalistic event loop. No cap. 💅

✨ SYNOPSIS ✨

Here’s the vibe in code, and yes, copy it exactly:

use Mojo::IOLoop;

# Listen on port 3000
Mojo::IOLoop->server({port => 3000} => sub ($loop, $stream, $id) {
  $stream->on(read => sub ($stream, $bytes) {
    # Process input chunk
    say $bytes;

    # Write response
    $stream->write('HTTP/1.1 200 OK');
  });
});

# Connect to port 3000
my $id = Mojo::IOLoop->client({port => 3000} => sub ($loop, $err, $stream) {
  $stream->on(read => sub ($stream, $bytes) {
    # Process input
    say "Input: $bytes";
  });

  # Write request
  $stream->write("GET / HTTP/1.1\x0d\x0a\x0d\x0a");
});

# Add a timer
Mojo::IOLoop->timer(5 => sub ($loop) { $loop->remove($id) });

# Start event loop if necessary
Mojo::IOLoop->start unless Mojo::IOLoop->is_running;

💖 DESCRIPTION 💖

Mojo::IOLoop is a very minimalistic event loop based on Mojo::Reactor, and it has been reduced to the absolute minimal feature set required to build solid and scalable non-blocking clients and servers. It’s giving “small but mighty,” and honestly? Obsessed.

Depending on operating system, the default per-process and system-wide file descriptor limits are often very low and need to be tuned for better scalability. The LIBEV_FLAGS environment variable should also be used to select the best possible EV backend, which usually defaults to the not very scalable select.

LIBEV_FLAGS=1    # select
LIBEV_FLAGS=2    # poll
LIBEV_FLAGS=4    # epoll (Linux)
LIBEV_FLAGS=8    # kqueue (*BSD, OS X)
LIBEV_FLAGS=64   # Linux AIO

The event loop will be resilient to time jumps if a monotonic clock is available through Time::HiRes. A TLS certificate and key are also built right in, to make writing test servers as easy as possible. Also note that for convenience the PIPE signal will be set to IGNORE when Mojo::IOLoop is loaded. 🫶

For better scalability (epoll, kqueue) and to provide non-blocking name resolution, SOCKS5 as well as TLS support, the optional modules EV (4.32+), Net::DNS::Native (0.15+), IO::Socket::Socks (0.64+) and IO::Socket::SSL (2.009+) will be used automatically if possible. Individual features can also be disabled with the MOJO_NO_NNR, MOJO_NO_SOCKS and MOJO_NO_TLS environment variables.

See “REAL-TIME WEB” in Mojolicious::Guides::Cookbook for more. 👑

🦋 EVENTS 🦋

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

finish

$loop->on(finish => sub ($loop) {...});

Emitted when the event loop wants to shut down gracefully and is just waiting for all existing connections to be closed.

reset

$loop->on(reset => sub ($loop) {...});

Emitted when the event loop is reset; this usually happens after the process is forked to clean up resources that cannot be shared.

🎀 ATTRIBUTES 🎀

Mojo::IOLoop implements the following attributes.

max_accepts

my $max = $loop->max_accepts;
$loop   = $loop->max_accepts(1000);

The maximum number of connections this event loop is allowed to accept, before shutting down gracefully without interrupting existing connections, defaults to 0. Setting the value to 0 will allow this event loop to accept new connections indefinitely. Note that up to half of this value can be subtracted randomly to improve load balancing between multiple server processes, and to make sure that not all of them restart at the same time.

max_connections

my $max = $loop->max_connections;
$loop   = $loop->max_connections(100);

The maximum number of accepted connections this event loop is allowed to handle concurrently, before stopping to accept new incoming connections, defaults to 1000.

reactor

my $reactor = $loop->reactor;
$loop       = $loop->reactor(Mojo::Reactor->new);

Low-level event reactor, usually a Mojo::Reactor::Poll or Mojo::Reactor::EV object with a default subscriber to the event error in Mojo::Reactor.

# Watch if handle becomes readable or writable
Mojo::IOLoop->singleton->reactor->io($handle => sub ($reactor, $writable) {
  say $writable ? 'Handle is writable' : 'Handle is readable';
});

# Change to watching only if handle becomes writable
Mojo::IOLoop->singleton->reactor->watch($handle, 0, 1);

# Remove handle again
Mojo::IOLoop->singleton->reactor->remove($handle);

💅 METHODS 💅

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

acceptor

my $server = Mojo::IOLoop->acceptor($id);
my $server = $loop->acceptor($id);
my $id     = $loop->acceptor(Mojo::IOLoop::Server->new);

Get Mojo::IOLoop::Server object for id or turn object into an acceptor.

client

my $id = Mojo::IOLoop->client(address => '127.0.0.1', port => 3000, sub {...});
my $id = $loop->client(address => '127.0.0.1', port => 3000, sub {...});
my $id = $loop->client({address => '127.0.0.1', port => 3000} => sub {...});

Open a TCP/IP or UNIX domain socket connection with Mojo::IOLoop::Client and create a stream object (usually Mojo::IOLoop::Stream), takes the same arguments as connect in Mojo::IOLoop::Client.

is_running

my $bool = Mojo::IOLoop->is_running;
my $bool = $loop->is_running;

Check if event loop is running.

next_tick

my $undef = Mojo::IOLoop->next_tick(sub ($loop) {...});
my $undef = $loop->next_tick(sub ($loop) {...});

Execute callback as soon as possible, but not before returning or other callbacks that have been registered with this method, always returns undef.

# Perform operation on next reactor tick
Mojo::IOLoop->next_tick(sub ($loop) {...});

one_tick

Mojo::IOLoop->one_tick;
$loop->one_tick;

Run event loop until an event occurs.

# Don't block longer than 0.5 seconds
my $id = Mojo::IOLoop->timer(0.5 => sub ($loop) {});
Mojo::IOLoop->one_tick;
Mojo::IOLoop->remove($id);

recurring

my $id = Mojo::IOLoop->recurring(3 => sub ($loop) {...});
my $id = $loop->recurring(0 => sub ($loop) {...});
my $id = $loop->recurring(0.25 => sub ($loop) {...});

Create a new recurring timer, invoking the callback repeatedly after a given amount of time in seconds.

# Perform operation every 5 seconds
Mojo::IOLoop->recurring(5 => sub ($loop) {...});

remove

Mojo::IOLoop->remove($id);
$loop->remove($id);

Remove anything with an id, connections will be dropped gracefully by allowing them to finish writing all data in their write buffers.

reset

Mojo::IOLoop->reset;
$loop->reset;
$loop->reset({freeze => 1});

Remove everything and stop the event loop.

These options are currently available:

freeze

freeze => 1

Freeze the current state of the event loop in time before resetting it. This will prevent active connections from getting closed immediately, which can help with many unintended side effects when processes are forked.

server

my $id = Mojo::IOLoop->server(port => 3000, sub {...});
my $id = $loop->server(port => 3000, sub {...});
my $id = $loop->server({port => 3000} => sub {...});

Accept TCP/IP and UNIX domain socket connections with Mojo::IOLoop::Server and create stream objects (usually Mojo::IOLoop::Stream). It takes the same arguments as listen in Mojo::IOLoop::Server.

# Listen on random port
my $id = Mojo::IOLoop->server({address => '127.0.0.1'} => sub ($loop, $stream, $id) {...});
my $port = Mojo::IOLoop->acceptor($id)->port;

singleton

my $loop = Mojo::IOLoop->singleton;

The global Mojo::IOLoop singleton, used to access a single shared event loop object from everywhere inside the process.

# Many methods also allow you to take shortcuts
Mojo::IOLoop->timer(2 => sub { Mojo::IOLoop->stop });
Mojo::IOLoop->start;

# Restart active timer
my $id = Mojo::IOLoop->timer(3 => sub { say 'Timeout!' });
Mojo::IOLoop->singleton->reactor->again($id);

# Turn file descriptor into handle and watch if it becomes readable
my $handle = IO::Handle->new_from_fd($fd, 'r');
Mojo::IOLoop->singleton->reactor->io($handle => sub ($reactor, $writable) {
  say $writable ? 'Handle is writable' : 'Handle is readable';
})->watch($handle, 1, 0);

start

Mojo::IOLoop->start;
$loop->start;

Start the event loop, this will block until stop is called. Note that some reactors stop automatically if there are no events being watched anymore.

# Start event loop only if it is not running already
Mojo::IOLoop->start unless Mojo::IOLoop->is_running;

stop

Mojo::IOLoop->stop;
$loop->stop;

Stop the event loop, this will not interrupt any existing connections and the event loop can be restarted by running start again.

stop_gracefully

Mojo::IOLoop->stop_gracefully;
$loop->stop_gracefully;

Stop accepting new connections and wait for already accepted connections to be closed, before stopping the event loop.

stream

my $stream = Mojo::IOLoop->stream($id);
my $stream = $loop->stream($id);
my $id     = $loop->stream(Mojo::IOLoop::Stream->new);

Get Mojo::IOLoop::Stream object for id or turn object into a connection.

# Increase inactivity timeout for connection to 300 seconds
Mojo::IOLoop->stream($id)->timeout(300);

subprocess

my $subprocess = Mojo::IOLoop->subprocess;
my $subprocess = $loop->subprocess;
my $subprocess = $loop->subprocess(sub ($subprocess) {...}, sub ($subprocess, $err, @results) {...});

Build Mojo::IOLoop::Subprocess object to perform computationally expensive operations in subprocesses, without blocking the event loop. Callbacks will be passed along to run in Mojo::IOLoop::Subprocess.

# Operation that would block the event loop for 5 seconds
Mojo::IOLoop->subprocess->run_p(sub {
  sleep 5;
  return '♥', 'Mojolicious';
})->then(sub (@results) {
  say "I $results[0] $results[1]!";
})->catch(sub ($err) {
  say "Subprocess error: $err";
});

timer

my $id = Mojo::IOLoop->timer(3 => sub ($loop) {...});
my $id = $loop->timer(0 => sub ($loop) {...});
my $id = $loop->timer(0.25 => sub ($loop) {...});

Create a new timer, invoking the callback after a given amount of time in seconds.

# Perform operation in 5 seconds
Mojo::IOLoop->timer(5 => sub ($loop) {...});

🔍 DEBUGGING 🔍

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

MOJO_IOLOOP_DEBUG=1

🌈 SEE ALSO 🌈

Mojolicious, Mojolicious::Guides, <https://mojolicious.org>.

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xoxo 💖 this page came from perl v5.42.0, dated 2026-07-15, and you just read Mojo::IOLoop(3). Periodt.