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 = 0.5;

=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:	1.19
Committed:	Sun Sep 16 01:34:36 2001 UTC (22 years, 8 months ago) by root
Branch:	MAIN
Changes since 1.18:	+1 -1 lines
Log Message:	* empty log message *
#	Content
1	=head1 NAME
2
3	Coro::Semaphore - non-binary semaphores
4
5	=head1 SYNOPSIS
6
7	use Coro::Semaphore;
8
9	$sig = new Coro::Semaphore [initial value];
10
11	$sig->down; # wait for signal
12
13	# ... some other "thread"
14
15	$sig->up;
16
17	=head1 DESCRIPTION
18
19	This module implements counting semaphores. You can initialize a mutex
20	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	=over 4
31
32	=cut
33
34	package Coro::Semaphore;
35
36	use Coro ();
37
38	$VERSION = 0.5;
39
40	=item new [inital count]
41
42	Creates a new sempahore object with the given initial lock count. The
43	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
47	=cut
48
49	sub new {
50	bless [defined $_[1] ? $_[1] : 1], $_[0];
51	}
52
53	=item $sem->down
54
55	Decrement the counter, therefore "locking" the semaphore. This method
56	waits until the semaphore is available if the counter is zero.
57
58	=cut
59
60	sub down {
61	while ($_[0][0] <= 0) {
62	push @{$_[0][1]}, $Coro::current;
63	Coro::schedule;
64	}
65	--$_[0][0];
66	}
67
68	=item $sem->up
69
70	Unlock the semaphore again.
71
72	=cut
73
74	sub up {
75	if (++$_[0][0] > 0) {
76	(shift @{$_[0][1]})->ready if @{$_[0][1]};
77	}
78	}
79
80	=item $sem->try
81
82	Try to C<down> the semaphore. Returns true when this was possible,
83	otherwise return false and leave the semaphore unchanged.
84
85	=cut
86
87	sub try {
88	if ($_[0][0] > 0) {
89	--$_[0][0];
90	return 1;
91	} else {
92	return 0;
93	}
94	}
95
96	=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	=item $guard = $sem->guard
108
109	This method calls C<down> and then creates a guard object. When the guard
110	object is destroyed it automatically calls C<up>.
111
112	=cut
113
114	sub guard {
115	&down;
116	# double indirection because bless works on the referenced
117	# object, not (only) on the reference itself.
118	bless \\$_[0], Coro::Semaphore::Guard::;
119	}
120
121	sub Coro::Semaphore::Guard::DESTROY {
122	&up(${${$_[0]}});
123	}
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