Channel(3) User Contributed Perl Documentation Channel(3)NAMECoro::Channel - message queues
SYNOPSIS
use Coro;
$q1 = new Coro::Channel <maxsize>;
$q1->put ("xxx");
print $q1->get;
die unless $q1->size;
DESCRIPTION
A Coro::Channel is the equivalent of a unix pipe (and similar to amiga
message ports): you can put things into it on one end and read things
out of it from the other end. If the capacity of the Channel is maxed
out writers will block. Both ends of a Channel can be read/written from
by as many coroutines as you want concurrently.
You don't have to load "Coro::Channel" manually, it will be loaded
automatically when you "use Coro" and call the "new" constructor.
$q = new Coro:Channel $maxsize
Create a new channel with the given maximum size (practically
unlimited if "maxsize" is omitted). Giving a size of one gives you
a traditional channel, i.e. a queue that can store only a single
element (which means there will be no buffering, and "put" will
wait until there is a corresponding "get" call). To buffer one
element you have to specify 2, and so on.
$q->put ($scalar)
Put the given scalar into the queue.
$q->get
Return the next element from the queue, waiting if necessary.
$q->shutdown
Shuts down the Channel by pushing a virtual end marker onto it:
This changes the behaviour of the Channel when it becomes or is
empty to return "undef", almost as if infinitely many "undef"
elements have been put into the queue.
Specifically, this function wakes up any pending "get" calls and
lets them return "undef", the same on future "get" calls. "size"
will return the real number of stored elements, though.
Another way to describe the behaviour is that "get" calls will not
block when the queue becomes empty but immediately return "undef".
This means that calls to "put" will work normally and the data will
be returned on subsequent "get" calls.
This method is useful to signal the end of data to any consumers,
quite similar to an end of stream on e.g. a tcp socket: You have
one or more producers that "put" data into the Channel and one or
more consumers who "get" them. When all producers have finished
producing data, a call to "shutdown" signals this fact to any
consumers.
$q->size
Return the number of elements waiting to be consumed. Please note
that:
if ($q->size) {
my $data = $q->get;
...
}
is not a race condition but instead works just fine. Note that the
number of elements that wait can be larger than $maxsize, as it
includes any coroutines waiting to put data into the channel (but
not any shutdown condition).
This means that the number returned is precisely the number of
calls to "get" that will succeed instantly and return some data.
Calling "shutdown" has no effect on this number.
AUTHOR
Marc Lehmann <schmorp@schmorp.de>
http://home.schmorp.de/
perl v5.14.2 2011-11-11 Channel(3)
