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1 | package Thread::Semaphore; |
2 | use Thread qw(cond_wait cond_broadcast); | |
3 | ||
d516a115 JH |
4 | =head1 NAME |
5 | ||
6 | Thread::Semaphore - thread-safe semaphores | |
7 | ||
8 | =head1 SYNOPSIS | |
9 | ||
10 | use Thread::Semaphore; | |
11 | my $s = new Thread::Semaphore; | |
12 | $s->up; # Also known as the semaphore V -operation. | |
13 | # The guarded section is here | |
14 | $s->down; # Also known as the semaphore P -operation. | |
15 | ||
16 | # The default semaphore value is 1. | |
17 | my $s = new Thread::Semaphore($initial_value); | |
18 | $s->up($up_value); | |
19 | $s->down($up_value); | |
20 | ||
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21 | =head1 DESCRIPTION |
22 | ||
23 | Semaphores provide a mechanism to regulate access to resources. Semaphores, | |
24 | unlike locks, aren't tied to particular scalars, and so may be used to | |
25 | control access to anything you care to use them for. | |
26 | ||
27 | Semaphores don't limit their values to zero or one, so they can be used to | |
28 | control access to some resource that may have more than one of. (For | |
29 | example, filehandles) Increment and decrement amounts aren't fixed at one | |
30 | either, so threads can reserve or return multiple resources at once. | |
31 | ||
32 | =head1 FUNCTIONS AND METHODS | |
33 | ||
34 | =over 8 | |
35 | ||
36 | =item new | |
37 | ||
38 | =item new NUMBER | |
39 | ||
40 | C<new> creates a new semaphore, and initializes its count to the passed | |
41 | number. If no number is passed, the semaphore's count is set to one. | |
42 | ||
43 | =item down | |
44 | ||
45 | =item down NUMBER | |
46 | ||
47 | The C<down> method decreases the semaphore's count by the specified number, | |
48 | or one if no number has been specified. If the semaphore's count would drop | |
49 | below zero, this method will block until such time that the semaphore's | |
50 | count is equal to or larger than the amount you're C<down>ing the | |
51 | semaphore's count by. | |
52 | ||
53 | =item up | |
54 | ||
55 | =item up NUMBER | |
56 | ||
57 | The C<up> method increases the semaphore's count by the number specified, | |
58 | or one if no number's been specified. This will unblock any thread blocked | |
59 | trying to C<down> the semaphore if the C<up> raises the semaphore count | |
60 | above what the C<down>s are trying to decrement it by. | |
61 | ||
62 | =back | |
63 | ||
d516a115 JH |
64 | =cut |
65 | ||
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66 | sub new { |
67 | my $class = shift; | |
68 | my $val = @_ ? shift : 1; | |
69 | bless \$val, $class; | |
70 | } | |
71 | ||
72 | sub down { | |
73 | use attrs qw(locked method); | |
74 | my $s = shift; | |
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75 | my $inc = @_ ? shift : 1; |
76 | cond_wait $s until $$s >= $inc; | |
77 | $$s -= $inc; | |
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78 | } |
79 | ||
80 | sub up { | |
81 | use attrs qw(locked method); | |
82 | my $s = shift; | |
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83 | my $inc = @_ ? shift : 1; |
84 | ($$s += $inc) > 0 and cond_broadcast $s; | |
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85 | } |
86 | ||
87 | 1; |