Coro/Coro/Channel.pm

=head1 NAME

Coro::Channel - message queues

=head1 SYNOPSIS

 use Coro::Channel;

 $q1 = new Coro::Channel <maxsize>;

 $q1->put ("xxx");
 print $q1->get;

 die unless $q1->size;

=head1 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.

=over 4

=cut

package Coro::Channel;

use common::sense;

use Coro ();
use Coro::Semaphore ();

our $VERSION = 5.2;

sub DATA (){ 0 }
sub SGET (){ 1 }
sub SPUT (){ 2 }
sub CEOS (){ 3 }

=item $q = new Coro:Channel $maxsize

Create a new channel with the given maximum size (practically unlimited
if C<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 C<put> will wait until there is a
corresponding C<get> call). To buffer one element you have to specify
C<2>, and so on.

=cut

sub new {
   # we cheat and set infinity == 2*10**9
   bless [
      [],
      (Coro::Semaphore::_alloc 0),
      (Coro::Semaphore::_alloc +($_[1] || 2_000_000_000) - 1),
   ]
}

=item $q->put ($scalar)

Put the given scalar into the queue.

=cut

sub put {
   push @{$_[0][DATA]}, $_[1];
   Coro::Semaphore::up   $_[0][SGET];
   Coro::Semaphore::down $_[0][SPUT];
}

=item $q->get

Return the next element from the queue, waiting if necessary.

=cut

sub get {
   Coro::Semaphore::down $_[0][SGET];
   Coro::Semaphore::up   $_[0][SPUT];
   shift @{$_[0][DATA]}
}

=item $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
C<undef>, almost as if infinitely many C<undef> elements have been put
into the queue.

Specifically, this function wakes up any pending C<get> calls and lets
them return C<undef>, the same on future C<get> calls. C<size> will return
the real number of stored elements, though.

Another way to describe the behaviour is that C<get> calls will not block
when the queue becomes empty but immediately return C<undef>. This means
that calls to C<put> will work normally and the data will be returned on
subsequent C<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 C<put> data into the Channel and one or more consumers who
C<get> them. When all producers have finished producing data, a call to
C<shutdown> signals this fact to any consumers.

=cut

sub shutdown {
   Coro::Semaphore::adjust $_[0][SGET], 2_000_000_000;
}

=item $q->size

Return the number of elements waiting to be consumed. Please note that:

  if ($q->size) {
     my $data = $q->get;
     ...
  }

is I<not> a race condition but instead works just fine. Note that the
number of elements that wait can be larger than C<$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 I<precisely> the number of calls to
C<get> that will succeed instantly and return some data.

=cut

sub size {
   scalar @{$_[0][DATA]}
}

1;

=back

=head1 AUTHOR

 Marc Lehmann <schmorp@schmorp.de>
 http://home.schmorp.de/

=cut

Revision:	1.94
Committed:	Tue Dec 1 00:02:08 2009 UTC (14 years, 6 months ago) by root
Branch:	MAIN
Changes since 1.93:	+1 -1 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	=head1 NAME
2
3			Coro::Channel - message queues
4
5			=head1 SYNOPSIS
6
7			use Coro::Channel;
8
9			$q1 = new Coro::Channel <maxsize>;
10
11	root	1.46	$q1->put ("xxx");
12	root	1.1	print $q1->get;
13
14			die unless $q1->size;
15
16			=head1 DESCRIPTION
17
18	root	1.75	A Coro::Channel is the equivalent of a unix pipe (and similar to amiga
19			message ports): you can put things into it on one end and read things out
20			of it from the other end. If the capacity of the Channel is maxed out
21			writers will block. Both ends of a Channel can be read/written from by as
22			many coroutines as you want concurrently.
23	root	1.8
24	root	1.1	=over 4
25
26			=cut
27
28			package Coro::Channel;
29
30	root	1.92	use common::sense;
31	root	1.45
32	root	1.3	use Coro ();
33	root	1.71	use Coro::Semaphore ();
34	root	1.1
35	root	1.93	our $VERSION = 5.2;
36	root	1.1
37	root	1.70	sub DATA (){ 0 }
38	root	1.71	sub SGET (){ 1 }
39			sub SPUT (){ 2 }
40	root	1.77	sub CEOS (){ 3 }
41	root	1.70
42	root	1.1	=item $q = new Coro:Channel $maxsize
43
44	root	1.75	Create a new channel with the given maximum size (practically unlimited
45			if C<maxsize> is omitted). Giving a size of one gives you a traditional
46			channel, i.e. a queue that can store only a single element (which means
47			there will be no buffering, and C<put> will wait until there is a
48			corresponding C<get> call). To buffer one element you have to specify
49			C<2>, and so on.
50	root	1.1
51			=cut
52
53			sub new {
54	root	1.84	# we cheat and set infinity == 210*9
55	root	1.71	bless [
56			[],
57	root	1.73	(Coro::Semaphore::_alloc 0),
58	root	1.77	(Coro::Semaphore::_alloc +($_[1] \|\| 2_000_000_000) - 1),
59	root	1.71	]
60	root	1.1	}
61
62	root	1.44	=item $q->put ($scalar)
63	root	1.1
64			Put the given scalar into the queue.
65
66			=cut
67
68			sub put {
69	root	1.70	push @{$_[0][DATA]}, $_[1];
70	root	1.71	Coro::Semaphore::up $_[0][SGET];
71			Coro::Semaphore::down $_[0][SPUT];
72	root	1.1	}
73
74			=item $q->get
75
76			Return the next element from the queue, waiting if necessary.
77
78			=cut
79
80			sub get {
81	root	1.71	Coro::Semaphore::down $_[0][SGET];
82			Coro::Semaphore::up $_[0][SPUT];
83	root	1.70	shift @{$_[0][DATA]}
84	root	1.47	}
85
86	root	1.77	=item $q->shutdown
87
88			Shuts down the Channel by pushing a virtual end marker onto it: This
89			changes the behaviour of the Channel when it becomes or is empty to return
90			C<undef>, almost as if infinitely many C<undef> elements have been put
91			into the queue.
92
93			Specifically, this function wakes up any pending C<get> calls and lets
94			them return C<undef>, the same on future C<get> calls. C<size> will return
95			the real number of stored elements, though.
96
97			Another way to describe the behaviour is that C<get> calls will not block
98			when the queue becomes empty but immediately return C<undef>. This means
99			that calls to C<put> will work normally and the data will be returned on
100			subsequent C<get> calls.
101
102			This method is useful to signal the end of data to any consumers, quite
103			similar to an end of stream on e.g. a tcp socket: You have one or more
104			producers that C<put> data into the Channel and one or more consumers who
105			C<get> them. When all producers have finished producing data, a call to
106			C<shutdown> signals this fact to any consumers.
107
108			=cut
109
110			sub shutdown {
111	root	1.79	Coro::Semaphore::adjust $_[0][SGET], 2_000_000_000;
112	root	1.77	}
113
114	root	1.1	=item $q->size
115
116			Return the number of elements waiting to be consumed. Please note that:
117
118			if ($q->size) {
119			my $data = $q->get;
120	root	1.77	...
121	root	1.1	}
122
123	root	1.83	is I<not> a race condition but instead works just fine. Note that the
124			number of elements that wait can be larger than C<$maxsize>, as it
125			includes any coroutines waiting to put data into the channel (but not any
126			shutdown condition).
127
128			This means that the number returned is I<precisely> the number of calls to
129	root	1.94	C<get> that will succeed instantly and return some data.
130	root	1.1
131			=cut
132
133			sub size {
134	root	1.70	scalar @{$_[0][DATA]}
135	root	1.1	}
136
137			1;
138
139			=back
140
141			=head1 AUTHOR
142
143	root	1.35	Marc Lehmann <schmorp@schmorp.de>
144	root	1.33	http://home.schmorp.de/
145	root	1.1
146			=cut
147