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920dae64 AT |
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; |