NAME

       Mojo::IOLoop::Delay - Promises/A+ and flow-control helpers

SYNOPSIS

         use Mojo::IOLoop::Delay;

         # Synchronize multiple non-blocking operations
         my $delay = Mojo::IOLoop::Delay->new;
         $delay->steps(sub { say 'BOOM!' });
         for my $i (1 .. 10) {
           my $end = $delay->begin;
           Mojo::IOLoop->timer($i => sub {
             say 10 - $i;
             $end->();
           });
         }
         $delay->wait;

         # Sequentialize multiple non-blocking operations
         Mojo::IOLoop::Delay->new->steps(

           # 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, @args) = @_;
             Mojo::IOLoop->timer(1 => $delay->begin);
             Mojo::IOLoop->timer(3 => $delay->begin);
             say 'Third step in 3 seconds.';
           },

           # Third step (the end)
           sub {
             my ($delay, @args) = @_;
             say 'And done after 5 seconds total.';
           }
         )->wait;

DESCRIPTION

       Mojo::IOLoop::Delay adds flow-control helpers to Mojo::Promise, which can help you avoid deep nested
       closures that often result from continuation-passing style.

         use Mojo::IOLoop;

         # These deep nested closures are often referred to as "Callback Hell"
         Mojo::IOLoop->timer(3 => sub {
           my loop = shift;

           say '3 seconds';
           Mojo::IOLoop->timer(3 => sub {
             my $loop = shift;

             say '6 seconds';
             Mojo::IOLoop->timer(3 => sub {
               my $loop = shift;

               say '9 seconds';
               Mojo::IOLoop->stop;
             });
           });
         });

         Mojo::IOLoop->start;

       The idea behind Mojo::IOLoop::Delay is to turn the nested closures above into a flat series of closures.
       In the example below, the call to "begin" creates a code reference that we can pass to "timer" in
       Mojo::IOLoop as a callback, and that leads to the next closure in the series when executed.

         use Mojo::IOLoop;

         # Instead of nested closures we now have a simple chain of steps
         my $delay = Mojo::IOLoop->delay(
           sub {
             my $delay = shift;
             Mojo::IOLoop->timer(3 => $delay->begin);
           },
           sub {
             my $delay = shift;
             say '3 seconds';
             Mojo::IOLoop->timer(3 => $delay->begin);
           },
           sub {
             my $delay = shift;
             say '6 seconds';
             Mojo::IOLoop->timer(3 => $delay->begin);
           },
           sub {
             my $delay = shift;
             say '9 seconds';
           }
         );
         $delay->wait;

       Another positive side effect of this pattern is that we do not need to call "start" in Mojo::IOLoop and
       "stop" in Mojo::IOLoop manually, because we know exactly when our chain of "steps" has reached the end.
       So "wait" in Mojo::Promise can stop the event loop automatically if it had to be started at all in the
       first place.

ATTRIBUTES

       Mojo::IOLoop::Delay inherits all attributes from Mojo::Promise.

METHODS

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

   begin
         my $cb = $delay->begin;
         my $cb = $delay->begin($offset);
         my $cb = $delay->begin($offset, $len);

       Indicate an active event by incrementing the event counter, the returned code reference can be used as a
       callback, and needs to be executed when the event has completed to decrement the event counter again.
       When all code references generated by this method have been executed and the event counter has reached
       zero, "steps" will continue.

         # Capture all arguments except for the first one (invocant)
         my $delay = Mojo::IOLoop->delay(sub {
           my ($delay, $err, $stream) = @_;
           ...
         });
         Mojo::IOLoop->client({port => 3000} => $delay->begin);
         $delay->wait;

       Arguments passed to the returned code reference are spliced with the given offset and length, defaulting
       to an offset of 1 with no default length. The arguments are then combined in the same order "begin" was
       called, and passed together to the next step.

         # Capture all arguments
         my $delay = Mojo::IOLoop->delay(sub {
           my ($delay, $loop, $err, $stream) = @_;
           ...
         });
         Mojo::IOLoop->client({port => 3000} => $delay->begin(0));
         $delay->wait;

         # Capture only the second argument
         my $delay = Mojo::IOLoop->delay(sub {
           my ($delay, $err) = @_;
           ...
         });
         Mojo::IOLoop->client({port => 3000} => $delay->begin(1, 1));
         $delay->wait;

         # Capture and combine arguments
         my $delay = Mojo::IOLoop->delay(sub {
           my ($delay, $three_err, $three_stream, $four_err, $four_stream) = @_;
           ...
         });
         Mojo::IOLoop->client({port => 3000} => $delay->begin);
         Mojo::IOLoop->client({port => 4000} => $delay->begin);
         $delay->wait;

   pass
         $delay = $delay->pass;
         $delay = $delay->pass(@args);

       Shortcut for passing values between "steps".

         # Longer version
         $delay->begin(0)->(@args);

   steps
         $delay = $delay->steps(sub {...}, sub {...});

       Sequentialize multiple events, every time the event counter reaches zero a callback will run, the first
       one automatically runs during the next reactor tick unless it is delayed by incrementing the event
       counter. This chain will continue until there are no remaining callbacks, a callback does not increment
       the event counter or an exception gets thrown in a callback. Finishing the chain will also result in the
       promise being fulfilled, or if an exception got thrown it will be rejected.

SEE ALSO

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