Coro/Coro/Semaphore.pm

=head1 NAME

Coro::Semaphore - non-binary semaphores

=head1 SYNOPSIS

 use Coro::Semaphore;

 $sig = new Coro::Semaphore [initial value];

 $sig->down; # wait for signal

 # ... some other "thread"

 $sig->up;

=head1 DESCRIPTION

This module implements counting semaphores. You can initialize a mutex
with any level of parallel users, that is, you can intialize a sempahore
that can be C<down>ed more than once until it blocks. There is no owner
associated with semaphores, so one coroutine can C<down> it while another
can C<up> it.

Counting semaphores are typically used to coordinate access to
resources, with the semaphore count initialized to the number of free
resources. Coroutines then increment the count when resources are added
and decrement the count when resources are removed.

=over 4

=cut

package Coro::Semaphore;

use Coro ();

$VERSION = 0.49;

=item new [inital count]

Creates a new sempahore object with the given initial lock count. The
default lock count is 1, which means it is unlocked by default. Zero (or
negative values) are also allowed, in which case the semaphore is locked
by default.

=cut

sub new {
   bless [defined $_[1] ? $_[1] : 1], $_[0];
}

=item $sem->down

Decrement the counter, therefore "locking" the semaphore. This method
waits until the semaphore is available if the counter is zero.

=cut

sub down {
   while ($_[0][0] <= 0) {
      push @{$_[0][1]}, $Coro::current;
      Coro::schedule;
   }
   --$_[0][0];
}

=item $sem->up

Unlock the semaphore again.

=cut

sub up {
   if (++$_[0][0] > 0) {
      (shift @{$_[0][1]})->ready if @{$_[0][1]};
   }
}

=item $sem->try

Try to C<down> the semaphore. Returns true when this was possible,
otherwise return false and leave the semaphore unchanged.

=cut

sub try {
   if ($_[0][0] > 0) {
      --$_[0][0];
      return 1;
   } else {
      return 0;
   }
}

=item $sem->waiters

In scalar context, returns the number of coroutines waiting for this
semaphore.

=cut

sub waiters {
   @{$_[0][1]};
}

=item $guard = $sem->guard

This method calls C<down> and then creates a guard object. When the guard
object is destroyed it automatically calls C<up>.

=cut

sub guard {
   &down;
   # double indirection because bless works on the referenced
   # object, not (only) on the reference itself.
   bless \\$_[0], Coro::Semaphore::Guard::;
}

sub Coro::Semaphore::Guard::DESTROY {
   &up(${${$_[0]}});
}

1;

=back

=head1 AUTHOR

 Marc Lehmann <pcg@goof.com>
 http://www.goof.com/pcg/marc/

=cut

Revision:	1.18
Committed:	Sun Sep 2 01:03:53 2001 UTC (22 years, 9 months ago) by root
Branch:	MAIN
Changes since 1.17:	+1 -1 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	=head1 NAME
2
3			Coro::Semaphore - non-binary semaphores
4
5			=head1 SYNOPSIS
6
7			use Coro::Semaphore;
8
9	root	1.3	$sig = new Coro::Semaphore [initial value];
10	root	1.1
11			$sig->down; # wait for signal
12
13			# ... some other "thread"
14
15			$sig->up;
16
17			=head1 DESCRIPTION
18
19	root	1.16	This module implements counting semaphores. You can initialize a mutex
20	root	1.11	with any level of parallel users, that is, you can intialize a sempahore
21			that can be C<down>ed more than once until it blocks. There is no owner
22			associated with semaphores, so one coroutine can C<down> it while another
23			can C<up> it.
24
25			Counting semaphores are typically used to coordinate access to
26			resources, with the semaphore count initialized to the number of free
27			resources. Coroutines then increment the count when resources are added
28			and decrement the count when resources are removed.
29
30	root	1.1	=over 4
31
32			=cut
33
34			package Coro::Semaphore;
35
36	root	1.5	use Coro ();
37	root	1.1
38	root	1.18	$VERSION = 0.49;
39	root	1.1
40	root	1.16	=item new [inital count]
41	root	1.3
42			Creates a new sempahore object with the given initial lock count. The
43	root	1.11	default lock count is 1, which means it is unlocked by default. Zero (or
44			negative values) are also allowed, in which case the semaphore is locked
45			by default.
46	root	1.3
47			=cut
48
49	root	1.1	sub new {
50	root	1.2	bless [defined $_[1] ? $_[1] : 1], $_[0];
51	root	1.1	}
52
53	root	1.3	=item $sem->down
54
55			Decrement the counter, therefore "locking" the semaphore. This method
56			waits until the semaphore is available if the counter is zero.
57
58			=cut
59
60	root	1.1	sub down {
61	root	1.17	while ($_[0][0] <= 0) {
62			push @{$_[0][1]}, $Coro::current;
63	root	1.5	Coro::schedule;
64	root	1.1	}
65	root	1.17	--$_[0][0];
66	root	1.1	}
67
68	root	1.3	=item $sem->up
69
70			Unlock the semaphore again.
71
72			=cut
73
74	root	1.1	sub up {
75	root	1.17	if (++$_[0][0] > 0) {
76			(shift @{$_[0][1]})->ready if @{$_[0][1]};
77	root	1.1	}
78			}
79	root	1.3
80			=item $sem->try
81
82			Try to C<down> the semaphore. Returns true when this was possible,
83			otherwise return false and leave the semaphore unchanged.
84
85			=cut
86	root	1.1
87			sub try {
88	root	1.17	if ($_[0][0] > 0) {
89			--$_[0][0];
90	root	1.1	return 1;
91			} else {
92			return 0;
93			}
94	root	1.12	}
95
96	root	1.15	=item $sem->waiters
97
98			In scalar context, returns the number of coroutines waiting for this
99			semaphore.
100
101			=cut
102
103			sub waiters {
104			@{$_[0][1]};
105			}
106
107	root	1.12	=item $guard = $sem->guard
108
109			This method calls C<down> and then creates a guard object. When the guard
110			object is destroyed it automatically calls C<up>.
111
112			=cut
113
114			sub guard {
115	root	1.16	&down;
116	root	1.13	# double indirection because bless works on the referenced
117			# object, not (only) on the reference itself.
118			bless \\$_[0], Coro::Semaphore::Guard::;
119	root	1.12	}
120
121			sub Coro::Semaphore::Guard::DESTROY {
122	root	1.16	&up(${${$_[0]}});
123	root	1.1	}
124
125			1;
126
127			=back
128
129			=head1 AUTHOR
130
131			Marc Lehmann <pcg@goof.com>
132			http://www.goof.com/pcg/marc/
133
134			=cut
135