Mojo::IOLoop(3) User Contributed Perl Documentation Mojo::IOLoop(3)
NAME
Mojo::IOLoop - Minimalistic event loop
SYNOPSIS
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, it
has been reduced to the absolute minimal feature set required to build
solid and scalable non-blocking clients and servers.
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, 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 'H', '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(3), Mojolicious::Guides(3), <https://mojolicious.org>.
perl v5.34.3 2026-10-19 Mojo::IOLoop(3)
mojolicious 9.510.0 - Generated Thu Oct 22 09:30:35 CDT 2026