1Mojo::IOLoop::Delay(3)User Contributed Perl DocumentationMojo::IOLoop::Delay(3)
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NAME

6       Mojo::IOLoop::Delay - Promises/A+ and flow-control helpers
7

SYNOPSIS

9         use Mojo::IOLoop::Delay;
10
11         # 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
23         # Sequentialize multiple non-blocking operations
24         Mojo::IOLoop::Delay->new->steps(
25
26           # First step (simple timer)
27           sub {
28             my $delay = shift;
29             Mojo::IOLoop->timer(2 => $delay->begin);
30             say 'Second step in 2 seconds.';
31           },
32
33           # Second step (concurrent timers)
34           sub {
35             my ($delay, @args) = @_;
36             Mojo::IOLoop->timer(1 => $delay->begin);
37             Mojo::IOLoop->timer(3 => $delay->begin);
38             say 'Third step in 3 seconds.';
39           },
40
41           # Third step (the end)
42           sub {
43             my ($delay, @args) = @_;
44             say 'And done after 5 seconds total.';
45           }
46         )->wait;
47

DESCRIPTION

49       Mojo::IOLoop::Delay adds flow-control helpers to Mojo::Promise, which
50       can help you avoid deep nested closures that often result from
51       continuation-passing style.
52
53         use Mojo::IOLoop;
54
55         # These deep nested closures are often referred to as "Callback Hell"
56         Mojo::IOLoop->timer(3 => sub {
57           my $loop = shift;
58
59           say '3 seconds';
60           Mojo::IOLoop->timer(3 => sub {
61             my $loop = shift;
62
63             say '6 seconds';
64             Mojo::IOLoop->timer(3 => sub {
65               my $loop = shift;
66
67               say '9 seconds';
68               Mojo::IOLoop->stop;
69             });
70           });
71         });
72
73         Mojo::IOLoop->start;
74
75       The idea behind Mojo::IOLoop::Delay is to turn the nested closures
76       above into a flat series of closures. In the example below, the call to
77       "begin" creates a code reference that we can pass to "timer" in
78       Mojo::IOLoop as a callback, and that leads to the next closure in the
79       series when executed.
80
81         use Mojo::IOLoop;
82
83         # Instead of nested closures we now have a simple chain of steps
84         my $delay = Mojo::IOLoop->delay(
85           sub {
86             my $delay = shift;
87             Mojo::IOLoop->timer(3 => $delay->begin);
88           },
89           sub {
90             my $delay = shift;
91             say '3 seconds';
92             Mojo::IOLoop->timer(3 => $delay->begin);
93           },
94           sub {
95             my $delay = shift;
96             say '6 seconds';
97             Mojo::IOLoop->timer(3 => $delay->begin);
98           },
99           sub {
100             my $delay = shift;
101             say '9 seconds';
102           }
103         );
104         $delay->wait;
105
106       Another positive side effect of this pattern is that we do not need to
107       call "start" in Mojo::IOLoop and "stop" in Mojo::IOLoop manually,
108       because we know exactly when our chain of "steps" has reached the end.
109       So "wait" in Mojo::Promise can stop the event loop automatically if it
110       had to be started at all in the first place.
111

ATTRIBUTES

113       Mojo::IOLoop::Delay inherits all attributes from Mojo::Promise.
114

METHODS

116       Mojo::IOLoop::Delay inherits all methods from Mojo::Promise and
117       implements the following new ones.
118
119   begin
120         my $cb = $delay->begin;
121         my $cb = $delay->begin($offset);
122         my $cb = $delay->begin($offset, $len);
123
124       Indicate an active event by incrementing the event counter, the
125       returned code reference can be used as a callback, and needs to be
126       executed when the event has completed to decrement the event counter
127       again. When all code references generated by this method have been
128       executed and the event counter has reached zero, "steps" will continue.
129
130         # Capture all arguments except for the first one (invocant)
131         my $delay = Mojo::IOLoop->delay(sub {
132           my ($delay, $err, $stream) = @_;
133           ...
134         });
135         Mojo::IOLoop->client({port => 3000} => $delay->begin);
136         $delay->wait;
137
138       Arguments passed to the returned code reference are spliced with the
139       given offset and length, defaulting to an offset of 1 with no default
140       length. The arguments are then combined in the same order "begin" was
141       called, and passed together to the next step.
142
143         # Capture all arguments
144         my $delay = Mojo::IOLoop->delay(sub {
145           my ($delay, $loop, $err, $stream) = @_;
146           ...
147         });
148         Mojo::IOLoop->client({port => 3000} => $delay->begin(0));
149         $delay->wait;
150
151         # Capture only the second argument
152         my $delay = Mojo::IOLoop->delay(sub {
153           my ($delay, $err) = @_;
154           ...
155         });
156         Mojo::IOLoop->client({port => 3000} => $delay->begin(1, 1));
157         $delay->wait;
158
159         # Capture and combine arguments
160         my $delay = Mojo::IOLoop->delay(sub {
161           my ($delay, $three_err, $three_stream, $four_err, $four_stream) = @_;
162           ...
163         });
164         Mojo::IOLoop->client({port => 3000} => $delay->begin);
165         Mojo::IOLoop->client({port => 4000} => $delay->begin);
166         $delay->wait;
167
168   pass
169         $delay = $delay->pass;
170         $delay = $delay->pass(@args);
171
172       Shortcut for passing values between "steps".
173
174         # Longer version
175         $delay->begin(0)->(@args);
176
177   steps
178         $delay = $delay->steps(sub {...}, sub {...});
179
180       Sequentialize multiple events, every time the event counter reaches
181       zero a callback will run, the first one automatically runs during the
182       next reactor tick unless it is delayed by incrementing the event
183       counter. This chain will continue until there are no remaining
184       callbacks, a callback does not increment the event counter or an
185       exception gets thrown in a callback. Finishing the chain will also
186       result in the promise being fulfilled, or if an exception got thrown it
187       will be rejected.
188

SEE ALSO

190       Mojolicious, Mojolicious::Guides, <https://mojolicious.org>.
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194perl v5.32.0                      2020-07-28            Mojo::IOLoop::Delay(3)
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