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Sebastian Riedel


Mojo::IOLoop - Minimalistic event loop


  use Mojo::IOLoop;

  # Listen on port 3000
  Mojo::IOLoop->server({port => 3000} => sub {
    my ($loop, $stream) = @_;

    $stream->on(read => sub {
      my ($stream, $bytes) = @_;

      # Process input chunk
      say $bytes;

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

  # Connect to port 3000
  my $id = Mojo::IOLoop->client({port => 3000} => sub {
    my ($loop, $err, $stream) = @_;

    $stream->on(read => sub {
      my ($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 {
    my $loop = shift;

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


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 TCP 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)

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 (4.0+), Net::DNS::Native (0.15+), IO::Socket::Socks (0.64+) and IO::Socket::SSL (1.94+) will be used automatically if possible. Individual features can also be disabled with the MOJO_NO_NDN, MOJO_NO_SOCKS and MOJO_NO_TLS environment variables.

See "REAL-TIME WEB" in Mojolicious::Guides::Cookbook for more.


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


  $loop->on(finish => sub {
    my $loop = shift;

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


Mojo::IOLoop implements the following attributes.


  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.


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

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


  my $multi = $loop->multi_accept;
  $loop     = $loop->multi_accept(100);

Number of connections to accept at once, defaults to 50 or 1, depending on if the value of "max_connections" is smaller than 50.


  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
  $loop->reactor->io($handle => sub {
    my ($reactor, $writable) = @_;
    say $writable ? 'Handle is writable' : 'Handle is readable';

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

  # Remove handle again


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


  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.


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

Open TCP connection with Mojo::IOLoop::Client, takes the same arguments as "connect" in Mojo::IOLoop::Client.

  # Connect to on port 3000
  Mojo::IOLoop->client({port => 3000} => sub {
    my ($loop, $err, $stream) = @_;


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

Build Mojo::IOLoop::Delay object to manage callbacks and control the flow of events for this event loop, which can help you avoid deep nested closures that often result from continuation-passing style. Callbacks will be passed along to "steps" in Mojo::IOLoop::Delay.

  # Synchronize multiple events
  my $delay = Mojo::IOLoop->delay(sub { say 'BOOM!' });
  for my $i (1 .. 10) {
    my $end = $delay->begin;
    Mojo::IOLoop->timer($i => sub {
      say 10 - $i;

  # Sequentialize multiple events

    # First step (simple timer)
    sub {
      my $delay = shift;
      Mojo::IOLoop->timer(2 => $delay->begin);
      say 'Second step in 2 seconds.';

    # Second step (concurrent timers)
    sub {
      my $delay = shift;
      Mojo::IOLoop->timer(1 => $delay->begin);
      Mojo::IOLoop->timer(3 => $delay->begin);
      say 'Third step in 3 seconds.';

    # Third step (the end)
    sub { say 'And done after 5 seconds total.' }

  # Handle exceptions in all steps
    sub {
      my $delay = shift;
      die 'Intentional error';
    sub {
      my ($delay, @args) = @_;
      say 'Never actually reached.';
  )->catch(sub {
    my ($delay, $err) = @_;
    say "Something went wrong: $err";


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

Check if event loop is running.

  exit unless Mojo::IOLoop->is_running;


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

Invoke 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 {
    my $loop = shift;



Run event loop until an event occurs. Note that this method can recurse back into the reactor, so you need to be careful.

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


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

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 {
    my $loop = shift;



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



Remove everything and stop the event loop.


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

Accept TCP connections with Mojo::IOLoop::Server, takes the same arguments as "listen" in Mojo::IOLoop::Server.

  # Listen on port 3000
  Mojo::IOLoop->server({port => 3000} => sub {
    my ($loop, $stream, $id) = @_;

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


  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 });

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

  # 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($handle => sub {
    my ($reactor, $writable) = @_;
    say $writable ? 'Handle is writable' : 'Handle is readable';
  })->watch($handle, 1, 0);



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



Stop accepting new connections and wait for all existing connections to be closed before stopping the event loop.


  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


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

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 {
    my $loop = shift;


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



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