lib/Thread/Semaphore.pm

package Thread::Semaphore;

use threads::shared;

our $VERSION = '2.01';

=head1 NAME

Thread::Semaphore - thread-safe semaphores

=head1 SYNOPSIS

    use Thread::Semaphore;
    my $s = new Thread::Semaphore;
    $s->down;   # Also known as the semaphore P operation.
    # The guarded section is here
    $s->up;     # Also known as the semaphore V operation.

    # The default semaphore value is 1.
    my $s = new Thread::Semaphore($initial_value);
    $s->down($down_value);
    $s->up($up_value);

=head1 DESCRIPTION

Semaphores provide a mechanism to regulate access to resources. Semaphores,
unlike locks, aren't tied to particular scalars, and so may be used to
control access to anything you care to use them for.

Semaphores don't limit their values to zero or one, so they can be used to
control access to some resource that there may be more than one of. (For
example, filehandles.) Increment and decrement amounts aren't fixed at one
either, so threads can reserve or return multiple resources at once.

=head1 FUNCTIONS AND METHODS

=over 8

=item new

=item new NUMBER

C<new> creates a new semaphore, and initializes its count to the passed
number. If no number is passed, the semaphore's count is set to one.

=item down

=item down NUMBER

The C<down> method decreases the semaphore's count by the specified number,
or by one if no number has been specified. If the semaphore's count would drop
below zero, this method will block until such time that the semaphore's
count is equal to or larger than the amount you're C<down>ing the
semaphore's count by.

This is the semaphore "P operation" (the name derives from the Dutch
word "pak", which means "capture" -- the semaphore operations were
named by the late Dijkstra, who was Dutch).

=item up

=item up NUMBER

The C<up> method increases the semaphore's count by the number specified,
or by one if no number has been specified. This will unblock any thread blocked
trying to C<down> the semaphore if the C<up> raises the semaphore count
above the amount that the C<down>s are trying to decrement it by.

This is the semaphore "V operation" (the name derives from the Dutch
word "vrij", which means "release").

=back

=cut

sub new {
    my $class = shift;
    my $val : shared = @_ ? shift : 1;
    bless \$val, $class;
}

sub down {
    my $s = shift;
    lock($$s);
    my $inc = @_ ? shift : 1;
    cond_wait $$s until $$s >= $inc;
    $$s -= $inc;
}

sub up {
    my $s = shift;
    lock($$s);
    my $inc = @_ ? shift : 1;
    ($$s += $inc) > 0 and cond_broadcast $$s;
}

1;
Revision:	1.1
Committed:	Thu Jun 30 14:27:16 2005 UTC (21 years, 3 months ago) by root
Branch:	MAIN
CVS Tags:	PERL-5-8-7, HEAD
Branch point for:	PERL
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	package Thread::Semaphore;
2
3			use threads::shared;
4
5			our $VERSION = '2.01';
6
7			=head1 NAME
8
9			Thread::Semaphore - thread-safe semaphores
10
11			=head1 SYNOPSIS
12
13			use Thread::Semaphore;
14			my $s = new Thread::Semaphore;
15			$s->down; # Also known as the semaphore P operation.
16			# The guarded section is here
17			$s->up; # Also known as the semaphore V operation.
18
19			# The default semaphore value is 1.
20			my $s = new Thread::Semaphore($initial_value);
21			$s->down($down_value);
22			$s->up($up_value);
23
24			=head1 DESCRIPTION
25
26			Semaphores provide a mechanism to regulate access to resources. Semaphores,
27			unlike locks, aren't tied to particular scalars, and so may be used to
28			control access to anything you care to use them for.
29
30			Semaphores don't limit their values to zero or one, so they can be used to
31			control access to some resource that there may be more than one of. (For
32			example, filehandles.) Increment and decrement amounts aren't fixed at one
33			either, so threads can reserve or return multiple resources at once.
34
35			=head1 FUNCTIONS AND METHODS
36
37			=over 8
38
39			=item new
40
41			=item new NUMBER
42
43			C<new> creates a new semaphore, and initializes its count to the passed
44			number. If no number is passed, the semaphore's count is set to one.
45
46			=item down
47
48			=item down NUMBER
49
50			The C<down> method decreases the semaphore's count by the specified number,
51			or by one if no number has been specified. If the semaphore's count would drop
52			below zero, this method will block until such time that the semaphore's
53			count is equal to or larger than the amount you're C<down>ing the
54			semaphore's count by.
55
56			This is the semaphore "P operation" (the name derives from the Dutch
57			word "pak", which means "capture" -- the semaphore operations were
58			named by the late Dijkstra, who was Dutch).
59
60			=item up
61
62			=item up NUMBER
63
64			The C<up> method increases the semaphore's count by the number specified,
65			or by one if no number has been specified. This will unblock any thread blocked
66			trying to C<down> the semaphore if the C<up> raises the semaphore count
67			above the amount that the C<down>s are trying to decrement it by.
68
69			This is the semaphore "V operation" (the name derives from the Dutch
70			word "vrij", which means "release").
71
72			=back
73
74			=cut
75
76			sub new {
77			my $class = shift;
78			my $val : shared = @_ ? shift : 1;
79			bless \$val, $class;
80			}
81
82			sub down {
83			my $s = shift;
84			lock($$s);
85			my $inc = @_ ? shift : 1;
86			cond_wait $$s until $$s >= $inc;
87			$$s -= $inc;
88			}
89
90			sub up {
91			my $s = shift;
92			lock($$s);
93			my $inc = @_ ? shift : 1;
94			($$s += $inc) > 0 and cond_broadcast $$s;
95			}
96
97			1;