1Mojo::IOLoop::Delay(3)User Contributed Perl DocumentationMojo::IOLoop::Delay(3)
2
6 Mojo::IOLoop::Delay - Promises/A+ and flow-control helpers
7
9 use Mojo::IOLoop::Delay;
10 # Synchronize multiple non-blocking operations
12 my $delay = Mojo::IOLoop::Delay->new;
13 $delay->steps(sub { say 'BOOM!' });
14 for my $i (1 .. 10) {
15 my $end = $delay->begin;
16 Mojo::IOLoop->timer($i => sub {
17 say 10 - $i;
18 $end->();
19 });
20 }
21 $delay->wait;
22 # Sequentialize multiple non-blocking operations
24 Mojo::IOLoop::Delay->new->steps(
25 # First step (simple timer)
27 sub ($delay) {
28 Mojo::IOLoop->timer(2 => $delay->begin);
29 say 'Second step in 2 seconds.';
30 },
31 # Second step (concurrent timers)
33 sub ($delay, @args) {
34 Mojo::IOLoop->timer(1 => $delay->begin);
35 Mojo::IOLoop->timer(3 => $delay->begin);
36 say 'Third step in 3 seconds.';
37 },
38 # Third step (the end)
40 sub ($delay, @args) {
41 say 'And done after 5 seconds total.';
42 }
43 )->wait;
44
46 Mojo::IOLoop::Delay adds flow-control helpers to Mojo::Promise, which
47 can help you avoid deep nested closures that often result from
48 continuation-passing style.
49 use Mojo::IOLoop;
51 # These deep nested closures are often referred to as "Callback Hell"
53 Mojo::IOLoop->timer(3 => sub ($loop) {
54 say '3 seconds';
56 Mojo::IOLoop->timer(3 => sub ($loop) {
57 say '6 seconds';
59 Mojo::IOLoop->timer(3 => sub ($loop) {
60 say '9 seconds';
62 Mojo::IOLoop->stop;
63 });
64 });
65 });
66 Mojo::IOLoop->start;
68 The idea behind Mojo::IOLoop::Delay is to turn the nested closures
70 above into a flat series of closures. In the example below, the call to
71 "begin" creates a code reference that we can pass to "timer" in
72 Mojo::IOLoop as a callback, and that leads to the next closure in the
73 series when executed.
74 use Mojo::IOLoop;
76 # Instead of nested closures we now have a simple chain of steps
78 my $delay = Mojo::IOLoop->delay(
79 sub ($delay) { Mojo::IOLoop->timer(3 => $delay->begin) },
80 sub ($delay) {
81 say '3 seconds';
82 Mojo::IOLoop->timer(3 => $delay->begin);
83 },
84 sub ($delay) {
85 say '6 seconds';
86 Mojo::IOLoop->timer(3 => $delay->begin);
87 },
88 sub ($delay) { say '9 seconds' }
89 );
90 $delay->wait;
91 Another positive side effect of this pattern is that we do not need to
93 call "start" in Mojo::IOLoop and "stop" in Mojo::IOLoop manually,
94 because we know exactly when our chain of "steps" has reached the end.
95 So "wait" in Mojo::Promise can stop the event loop automatically if it
96 had to be started at all in the first place.
97
99 Mojo::IOLoop::Delay inherits all attributes from Mojo::Promise.
100
102 Mojo::IOLoop::Delay inherits all methods from Mojo::Promise and
103 implements the following new ones.
104 begin
106 my $cb = $delay->begin;
107 my $cb = $delay->begin($offset);
108 my $cb = $delay->begin($offset, $len);
109 Indicate an active event by incrementing the event counter, the
111 returned code reference can be used as a callback, and needs to be
112 executed when the event has completed to decrement the event counter
113 again. When all code references generated by this method have been
114 executed and the event counter has reached zero, "steps" will continue.
115 # Capture all arguments except for the first one (invocant)
117 my $delay = Mojo::IOLoop->delay(sub ($delay, $err, $stream) { ... });
118 Mojo::IOLoop->client({port => 3000} => $delay->begin);
119 $delay->wait;
120 Arguments passed to the returned code reference are spliced with the
122 given offset and length, defaulting to an offset of 1 with no default
123 length. The arguments are then combined in the same order "begin" was
124 called, and passed together to the next step.
125 # Capture all arguments
127 my $delay = Mojo::IOLoop->delay(sub ($delay, $loop, $err, $stream) { ... });
128 Mojo::IOLoop->client({port => 3000} => $delay->begin(0));
129 $delay->wait;
130 # Capture only the second argument
132 my $delay = Mojo::IOLoop->delay(sub ($delay, $err) { ... });
133 Mojo::IOLoop->client({port => 3000} => $delay->begin(1, 1));
134 $delay->wait;
135 # Capture and combine arguments
137 my $delay = Mojo::IOLoop->delay(sub ($delay, $three_err, $three_stream, $four_err, $four_stream) { ... });
138 Mojo::IOLoop->client({port => 3000} => $delay->begin);
139 Mojo::IOLoop->client({port => 4000} => $delay->begin);
140 $delay->wait;
141 pass
143 $delay = $delay->pass;
144 $delay = $delay->pass(@args);
145 Shortcut for passing values between "steps".
147 # Longer version
149 $delay->begin(0)->(@args);
150 steps
152 $delay = $delay->steps(sub {...}, sub {...});
153 Sequentialize multiple events, every time the event counter reaches
155 zero a callback will run, the first one automatically runs during the
156 next reactor tick unless it is delayed by incrementing the event
157 counter. This chain will continue until there are no remaining
158 callbacks, a callback does not increment the event counter or an
159 exception gets thrown in a callback. Finishing the chain will also
160 result in the promise being fulfilled, or if an exception got thrown it
161 will be rejected.
162
164 Mojolicious, Mojolicious::Guides, <https://mojolicious.org>.
165perl v5.32.1 2021-02-07 Mojo::IOLoop::Delay(3)