1Channel(3) User Contributed Perl Documentation Channel(3)
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6 Coro::Channel - message queues
7
9 use Coro;
10 $q1 = new Coro::Channel <maxsize>;
12 $q1->put ("xxx");
14 print $q1->get;
15 die unless $q1->size;
17
19 A Coro::Channel is the equivalent of a unix pipe (and similar to amiga
20 message ports): you can put things into it on one end and read things
21 out of it from the other end. If the capacity of the Channel is maxed
22 out writers will block. Both ends of a Channel can be read/written from
23 by as many coroutines as you want concurrently.
24 You don't have to load "Coro::Channel" manually, it will be loaded
26 automatically when you "use Coro" and call the "new" constructor.
27 $q = new Coro:Channel $maxsize
29 Create a new channel with the given maximum size (practically
30 unlimited if "maxsize" is omitted or zero). Giving a size of one
31 gives you a traditional channel, i.e. a queue that can store only a
32 single element (which means there will be no buffering, and "put"
33 will wait until there is a corresponding "get" call). To buffer one
34 element you have to specify 2, and so on.
35 $q->put ($scalar)
37 Put the given scalar into the queue.
38 $q->get
40 Return the next element from the queue, waiting if necessary.
41 $q->shutdown
43 Shuts down the Channel by pushing a virtual end marker onto it:
44 This changes the behaviour of the Channel when it becomes or is
45 empty to return "undef", almost as if infinitely many "undef"
46 elements had been put into the queue.
47 Specifically, this function wakes up any pending "get" calls and
49 lets them return "undef", the same on future "get" calls. "size"
50 will return the real number of stored elements, though.
51 Another way to describe the behaviour is that "get" calls will not
53 block when the queue becomes empty but immediately return "undef".
54 This means that calls to "put" will work normally and the data will
55 be returned on subsequent "get" calls.
56 This method is useful to signal the end of data to any consumers,
58 quite similar to an end of stream on e.g. a tcp socket: You have
59 one or more producers that "put" data into the Channel and one or
60 more consumers who "get" them. When all producers have finished
61 producing data, a call to "shutdown" signals this fact to any
62 consumers.
63 A common implementation uses one or more threads that "get" from a
65 channel until it returns "undef". To clean everything up, first
66 "shutdown" the channel, then "join" the threads.
67 $q->size
69 Return the number of elements waiting to be consumed. Please note
70 that:
71 if ($q->size) {
73 my $data = $q->get;
74 ...
75 }
76 is not a race condition but instead works just fine. Note that the
78 number of elements that wait can be larger than $maxsize, as it
79 includes any coroutines waiting to put data into the channel (but
80 not any shutdown condition).
81 This means that the number returned is precisely the number of
83 calls to "get" that will succeed instantly and return some data.
84 Calling "shutdown" has no effect on this number.
85
87 Marc A. Lehmann <schmorp@schmorp.de>
88 http://software.schmorp.de/pkg/Coro.html
89perl v5.28.0 2017-08-31 Channel(3)