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1 | package Thread::Semaphore; |
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2 | |
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3 | use threads::shared; |
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4 | |
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5 | our $VERSION = '2.01'; |
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6 | |
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7 | =head1 NAME |
8 | |
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9 | Thread::Semaphore - thread-safe semaphores |
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10 | |
11 | =head1 SYNOPSIS |
12 | |
13 | use Thread::Semaphore; |
14 | my $s = new Thread::Semaphore; |
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15 | $s->down; # Also known as the semaphore P operation. |
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16 | # The guarded section is here |
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17 | $s->up; # Also known as the semaphore V operation. |
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18 | |
19 | # The default semaphore value is 1. |
20 | my $s = new Thread::Semaphore($initial_value); |
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21 | $s->down($down_value); |
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22 | $s->up($up_value); |
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23 | |
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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 |
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31 | control access to some resource that there may be more than one of. (For |
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32 | example, filehandles.) Increment and decrement amounts aren't fixed at one |
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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, |
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51 | or by one if no number has been specified. If the semaphore's count would drop |
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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 | |
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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 | |
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60 | =item up |
61 | |
62 | =item up NUMBER |
63 | |
64 | The C<up> method increases the semaphore's count by the number specified, |
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65 | or by one if no number has been specified. This will unblock any thread blocked |
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66 | trying to C<down> the semaphore if the C<up> raises the semaphore count |
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67 | above the amount that the C<down>s are trying to decrement it by. |
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68 | |
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69 | This is the semaphore "V operation" (the name derives from the Dutch |
70 | word "vrij", which means "release"). |
71 | |
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72 | =back |
73 | |
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74 | =cut |
75 | |
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76 | sub new { |
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77 | my $class = shift; |
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78 | my $val : shared = @_ ? shift : 1; |
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79 | bless \$val, $class; |
80 | } |
81 | |
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82 | sub down { |
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83 | my $s = shift; |
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84 | lock($$s); |
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85 | my $inc = @_ ? shift : 1; |
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86 | cond_wait $$s until $$s >= $inc; |
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87 | $$s -= $inc; |
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88 | } |
89 | |
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90 | sub up { |
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91 | my $s = shift; |
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92 | lock($$s); |
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93 | my $inc = @_ ? shift : 1; |
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94 | ($$s += $inc) > 0 and cond_broadcast $$s; |
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95 | } |
96 | |
97 | 1; |