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83272a45 JH |
1 | package Thread::Semaphore; |
2 | use Thread qw(cond_wait cond_broadcast); | |
0b876b54 | 3 | |
f7229ad3 JH |
4 | use vars qw($VERSION); |
5 | $VERSION = '1.00'; | |
6 | ||
83272a45 | 7 | =head1 NAME |
0b876b54 | 8 | |
83272a45 | 9 | Thread::Semaphore - thread-safe semaphores (5.005-threads) |
0b876b54 | 10 | |
83272a45 JH |
11 | =head1 CAVEAT |
12 | ||
13 | This Perl installation is using the old unsupported "5.005 threads". | |
14 | Use of the old threads model is discouraged. | |
0b876b54 | 15 | |
83272a45 JH |
16 | For the whole story about the development of threads in Perl, and why |
17 | you should B<not> be using "old threads" unless you know what you're | |
18 | doing, see the CAVEAT of the C<Thread> module. | |
0b876b54 AB |
19 | |
20 | =head1 SYNOPSIS | |
21 | ||
83272a45 JH |
22 | use Thread::Semaphore; |
23 | my $s = new Thread::Semaphore; | |
0b876b54 AB |
24 | $s->up; # Also known as the semaphore V -operation. |
25 | # The guarded section is here | |
26 | $s->down; # Also known as the semaphore P -operation. | |
27 | ||
28 | # The default semaphore value is 1. | |
83272a45 | 29 | my $s = new Thread::Semaphore($initial_value); |
0b876b54 AB |
30 | $s->up($up_value); |
31 | $s->down($up_value); | |
32 | ||
33 | =head1 DESCRIPTION | |
34 | ||
35 | Semaphores provide a mechanism to regulate access to resources. Semaphores, | |
36 | unlike locks, aren't tied to particular scalars, and so may be used to | |
37 | control access to anything you care to use them for. | |
38 | ||
39 | Semaphores don't limit their values to zero or one, so they can be used to | |
83272a45 JH |
40 | control access to some resource that may have more than one of. (For |
41 | example, filehandles) Increment and decrement amounts aren't fixed at one | |
0b876b54 AB |
42 | either, so threads can reserve or return multiple resources at once. |
43 | ||
44 | =head1 FUNCTIONS AND METHODS | |
45 | ||
46 | =over 8 | |
47 | ||
48 | =item new | |
49 | ||
50 | =item new NUMBER | |
51 | ||
52 | C<new> creates a new semaphore, and initializes its count to the passed | |
53 | number. If no number is passed, the semaphore's count is set to one. | |
54 | ||
55 | =item down | |
56 | ||
57 | =item down NUMBER | |
58 | ||
59 | The C<down> method decreases the semaphore's count by the specified number, | |
83272a45 | 60 | or one if no number has been specified. If the semaphore's count would drop |
0b876b54 AB |
61 | below zero, this method will block until such time that the semaphore's |
62 | count is equal to or larger than the amount you're C<down>ing the | |
63 | semaphore's count by. | |
64 | ||
65 | =item up | |
66 | ||
67 | =item up NUMBER | |
68 | ||
69 | The C<up> method increases the semaphore's count by the number specified, | |
83272a45 | 70 | or one if no number's been specified. This will unblock any thread blocked |
0b876b54 | 71 | trying to C<down> the semaphore if the C<up> raises the semaphore count |
83272a45 | 72 | above what the C<down>s are trying to decrement it by. |
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73 | |
74 | =back | |
75 | ||
76 | =cut | |
77 | ||
78 | sub new { | |
79 | my $class = shift; | |
83272a45 | 80 | my $val = @_ ? shift : 1; |
0b876b54 AB |
81 | bless \$val, $class; |
82 | } | |
83 | ||
83272a45 | 84 | sub down : locked : method { |
0b876b54 | 85 | my $s = shift; |
0b876b54 | 86 | my $inc = @_ ? shift : 1; |
83272a45 | 87 | cond_wait $s until $$s >= $inc; |
0b876b54 AB |
88 | $$s -= $inc; |
89 | } | |
90 | ||
83272a45 | 91 | sub up : locked : method { |
0b876b54 | 92 | my $s = shift; |
0b876b54 | 93 | my $inc = @_ ? shift : 1; |
83272a45 | 94 | ($$s += $inc) > 0 and cond_broadcast $s; |
0b876b54 AB |
95 | } |
96 | ||
97 | 1; |