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
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8 |
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9 | Thread::Semaphore - thread-safe semaphores
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10 |
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11 | =head1 SYNOPSIS
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12 |
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13 | use Thread::Semaphore;
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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 |
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19 | # The default semaphore value is 1.
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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
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25 |
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26 | Semaphores provide a mechanism to regulate access to resources. Semaphores,
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27 | unlike locks, aren't tied to particular scalars, and so may be used to
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28 | control access to anything you care to use them for.
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29 |
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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.
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34 |
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35 | =head1 FUNCTIONS AND METHODS
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36 |
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37 | =over 8
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38 |
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39 | =item new
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40 |
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41 | =item new NUMBER
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42 |
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43 | C<new> creates a new semaphore, and initializes its count to the passed
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44 | number. If no number is passed, the semaphore's count is set to one.
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45 |
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46 | =item down
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47 |
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48 | =item down NUMBER
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49 |
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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
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53 | count is equal to or larger than the amount you're C<down>ing the
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54 | semaphore's count by.
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55 |
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56 | This is the semaphore "P operation" (the name derives from the Dutch
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57 | word "pak", which means "capture" -- the semaphore operations were
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58 | named by the late Dijkstra, who was Dutch).
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59 |
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60 | =item up
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61 |
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62 | =item up NUMBER
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63 |
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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
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70 | word "vrij", which means "release").
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71 |
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72 | =back
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73 |
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74 | =cut
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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;
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80 | }
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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 | }
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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 | }
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96 |
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97 | 1;
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