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=head1 NAME |
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|
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Coro::Channel - message queues |
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|
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=head1 SYNOPSIS |
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|
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use Coro; |
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|
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$q1 = new Coro::Channel <maxsize>; |
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|
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$q1->put ("xxx"); |
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print $q1->get; |
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|
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die unless $q1->size; |
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|
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=head1 DESCRIPTION |
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|
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A Coro::Channel is the equivalent of a unix pipe (and similar to amiga |
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message ports): you can put things into it on one end and read things out |
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of it from the other end. If the capacity of the Channel is maxed out |
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writers will block. Both ends of a Channel can be read/written from by as |
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many coroutines as you want concurrently. |
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|
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You don't have to load C<Coro::Channel> manually, it will be loaded |
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automatically when you C<use Coro> and call the C<new> constructor. |
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|
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=over 4 |
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|
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=cut |
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|
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package Coro::Channel; |
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|
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use common::sense; |
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|
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use Coro (); |
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use Coro::Semaphore (); |
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|
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our $VERSION = 6.57; |
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|
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sub DATA (){ 0 } |
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sub SGET (){ 1 } |
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sub SPUT (){ 2 } |
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|
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=item $q = new Coro:Channel $maxsize |
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|
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Create a new channel with the given maximum size (practically unlimited |
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if C<maxsize> is omitted or zero). Giving a size of one gives you a |
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traditional channel, i.e. a queue that can store only a single element |
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(which means there will be no buffering, and C<put> will wait until there |
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is a corresponding C<get> call). To buffer one element you have to specify |
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C<2>, and so on. |
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|
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=cut |
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|
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sub new { |
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# we cheat and set infinity == 2*10**9 |
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bless [ |
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[], # initially empty |
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(Coro::Semaphore::_alloc 0), # counts data |
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(Coro::Semaphore::_alloc +($_[1] || 2_000_000_000) - 1), # counts remaining space |
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] |
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} |
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|
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=item $q->put ($scalar) |
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|
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Put the given scalar into the queue. |
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|
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=cut |
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|
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sub put { |
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push @{$_[0][DATA]}, $_[1]; |
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Coro::Semaphore::up $_[0][SGET]; |
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Coro::Semaphore::down $_[0][SPUT]; |
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} |
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|
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=item $q->get |
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|
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Return the next element from the queue, waiting if necessary. |
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|
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=cut |
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|
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sub get { |
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Coro::Semaphore::down $_[0][SGET]; |
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Coro::Semaphore::up $_[0][SPUT]; |
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shift @{$_[0][DATA]} |
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} |
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|
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=item $q->shutdown |
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|
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Shuts down the Channel by pushing a virtual end marker onto it: This |
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changes the behaviour of the Channel when it becomes or is empty to return |
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C<undef>, almost as if infinitely many C<undef> elements had been put |
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into the queue. |
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|
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Specifically, this function wakes up any pending C<get> calls and lets |
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them return C<undef>, the same on future C<get> calls. C<size> will return |
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the real number of stored elements, though. |
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|
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Another way to describe the behaviour is that C<get> calls will not block |
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when the queue becomes empty but immediately return C<undef>. This means |
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that calls to C<put> will work normally and the data will be returned on |
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subsequent C<get> calls. |
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|
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This method is useful to signal the end of data to any consumers, quite |
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similar to an end of stream on e.g. a tcp socket: You have one or more |
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producers that C<put> data into the Channel and one or more consumers who |
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C<get> them. When all producers have finished producing data, a call to |
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C<shutdown> signals this fact to any consumers. |
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|
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A common implementation uses one or more threads that C<get> from |
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a channel until it returns C<undef>. To clean everything up, first |
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C<shutdown> the channel, then C<join> the threads. |
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|
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=cut |
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|
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sub shutdown { |
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Coro::Semaphore::adjust $_[0][SGET], 1_000_000_000; |
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} |
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|
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=item $q->size |
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|
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Return the number of elements waiting to be consumed. Please note that: |
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|
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if ($q->size) { |
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my $data = $q->get; |
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... |
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} |
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|
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is I<not> a race condition but instead works just fine. Note that the |
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number of elements that wait can be larger than C<$maxsize>, as it |
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includes any coroutines waiting to put data into the channel (but not any |
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shutdown condition). |
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|
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This means that the number returned is I<precisely> the number of calls |
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to C<get> that will succeed instantly and return some data. Calling |
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C<shutdown> has no effect on this number. |
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|
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=cut |
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|
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sub size { |
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scalar @{$_[0][DATA]} |
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} |
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|
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# this is not undocumented by accident - if it breaks, you |
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# get to keep the pieces |
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sub adjust { |
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Coro::Semaphore::adjust $_[0][SPUT], $_[1]; |
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} |
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|
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1; |
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|
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=back |
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|
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=head1 AUTHOR/SUPPORT/CONTACT |
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|
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Marc A. Lehmann <schmorp@schmorp.de> |
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http://software.schmorp.de/pkg/Coro.html |
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|
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=cut |
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