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Marcus Ramberg > Mojolicious-4.60 > Mojo::IOLoop



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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.

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 IPv6 as well as TLS support, the optional modules EV (4.0+), IO::Socket::IP (0.16+) and IO::Socket::SSL (1.75+) will be used automatically if they are installed. Individual features can also be disabled with the MOJO_NO_IPV6 and MOJO_NO_TLS environment variables.

See Mojolicious::Guides::Cookbook for more.


Mojo::IOLoop implements the following attributes.


  my $interval = $loop->accept_interval;
  $loop        = $loop->accept_interval(0.5);

Interval in seconds for trying to reacquire the accept mutex, defaults to 0.025. Note that changing this value can affect performance and idle CPU usage.


  my $cb = $loop->lock;
  $loop  = $loop->lock(sub {...});

A callback for acquiring the accept mutex, used to sync multiple server processes. The callback should return true or false. Note that exceptions in this callback are not captured.

  $loop->lock(sub {
    my ($loop, $blocking) = @_;

    # Got the accept mutex, start accepting new connections
    return 1;


  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 parallel connections this event loop is allowed to handle before stopping to accept new incoming connections, defaults to 1000. Setting the value to 0 will make this event loop stop accepting new connections and allow it to shut down gracefully without interrupting existing connections.


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

Number of connections to accept at once, defaults to 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 error event.

  # 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);


  my $cb = $loop->unlock;
  $loop  = $loop->unlock(sub {...});

A callback for releasing the accept mutex, used to sync multiple server processes. Note that exceptions in this callback are not captured.


Mojo::IOLoop inherits all methods from Mojo::Base 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 localhost 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 {...});

Get Mojo::IOLoop::Delay object to manage callbacks and control the flow of events. A single callback will be treated as a subscriber to the finish event, and multiple ones as a chain of steps.

  # 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;
  $delay->wait unless Mojo::IOLoop->is_running;

  # Sequentialize multiple events
  my $delay = Mojo::IOLoop->delay(

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

    # Second step (parallel 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.' }
  $delay->wait unless Mojo::IOLoop->is_running;


  my $port = Mojo::IOLoop->generate_port;
  my $port = $loop->generate_port;

Find a free TCP port, this is a utility function primarily used for tests.


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

Check if event loop is running.

  exit unless Mojo::IOLoop->is_running;



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(0.5 => sub {...});
  my $id = $loop->recurring(3 => sub {...});

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

  # Invoke as soon as possible
  Mojo::IOLoop->recurring(0 => sub { say 'Reactor tick.' });



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


  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) = @_;


  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!' });



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.


  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(5 => sub {...});
  my $id = $loop->timer(5 => sub {...});
  my $id = $loop->timer(0.25 => sub {...});

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

  # Invoke as soon as possible
  Mojo::IOLoop->timer(0 => sub { say 'Next tick.' });


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



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