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 strict qw(vars subs);
no warnings;

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

our $VERSION = 5.13;

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 == 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.

=cut

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

1;

=back

=head1 AUTHOR

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

=cut

Revision:	1.80
Committed:	Sat Dec 13 22:08:13 2008 UTC (15 years, 5 months ago) by root
Branch:	MAIN
CVS Tags:	rel-6_13
Changes since 1.79:	+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	1.60	use strict qw(vars subs);
31	root	1.45	no warnings;
32
33	root	1.3	use Coro ();
34	root	1.71	use Coro::Semaphore ();
35	root	1.1
36	root	1.80	our $VERSION = 5.13;
37	root	1.1
38	root	1.70	sub DATA (){ 0 }
39	root	1.71	sub SGET (){ 1 }
40			sub SPUT (){ 2 }
41	root	1.77	sub CEOS (){ 3 }
42	root	1.70
43	root	1.1	=item $q = new Coro:Channel $maxsize
44
45	root	1.75	Create a new channel with the given maximum size (practically unlimited
46			if C<maxsize> is omitted). Giving a size of one gives you a traditional
47			channel, i.e. a queue that can store only a single element (which means
48			there will be no buffering, and C<put> will wait until there is a
49			corresponding C<get> call). To buffer one element you have to specify
50			C<2>, and so on.
51	root	1.1
52			=cut
53
54			sub new {
55	root	1.71	# we cheat and set infinity == 10**9
56			bless [
57			[],
58	root	1.73	(Coro::Semaphore::_alloc 0),
59	root	1.77	(Coro::Semaphore::_alloc +($_[1] \|\| 2_000_000_000) - 1),
60	root	1.71	]
61	root	1.1	}
62
63	root	1.44	=item $q->put ($scalar)
64	root	1.1
65			Put the given scalar into the queue.
66
67			=cut
68
69			sub put {
70	root	1.70	push @{$_[0][DATA]}, $_[1];
71	root	1.71	Coro::Semaphore::up $_[0][SGET];
72			Coro::Semaphore::down $_[0][SPUT];
73	root	1.1	}
74
75			=item $q->get
76
77			Return the next element from the queue, waiting if necessary.
78
79			=cut
80
81			sub get {
82	root	1.71	Coro::Semaphore::down $_[0][SGET];
83			Coro::Semaphore::up $_[0][SPUT];
84	root	1.70	shift @{$_[0][DATA]}
85	root	1.47	}
86
87	root	1.77	=item $q->shutdown
88
89			Shuts down the Channel by pushing a virtual end marker onto it: This
90			changes the behaviour of the Channel when it becomes or is empty to return
91			C<undef>, almost as if infinitely many C<undef> elements have been put
92			into the queue.
93
94			Specifically, this function wakes up any pending C<get> calls and lets
95			them return C<undef>, the same on future C<get> calls. C<size> will return
96			the real number of stored elements, though.
97
98			Another way to describe the behaviour is that C<get> calls will not block
99			when the queue becomes empty but immediately return C<undef>. This means
100			that calls to C<put> will work normally and the data will be returned on
101			subsequent C<get> calls.
102
103			This method is useful to signal the end of data to any consumers, quite
104			similar to an end of stream on e.g. a tcp socket: You have one or more
105			producers that C<put> data into the Channel and one or more consumers who
106			C<get> them. When all producers have finished producing data, a call to
107			C<shutdown> signals this fact to any consumers.
108
109			=cut
110
111			sub shutdown {
112	root	1.79	Coro::Semaphore::adjust $_[0][SGET], 2_000_000_000;
113	root	1.77	}
114
115	root	1.1	=item $q->size
116
117			Return the number of elements waiting to be consumed. Please note that:
118
119			if ($q->size) {
120			my $data = $q->get;
121	root	1.77	...
122	root	1.1	}
123
124	root	1.75	is I<not> a race condition but instead works just fine.
125	root	1.1
126			=cut
127
128			sub size {
129	root	1.70	scalar @{$_[0][DATA]}
130	root	1.1	}
131
132			1;
133
134			=back
135
136			=head1 AUTHOR
137
138	root	1.35	Marc Lehmann <schmorp@schmorp.de>
139	root	1.33	http://home.schmorp.de/
140	root	1.1
141			=cut
142