[14489] | 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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