| 1 | package Thread::Semaphore; |
| 2 | |
| 3 | use threads::shared; |
| 4 | |
| 5 | our $VERSION = '2.00'; |
| 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->up; # Also known as the semaphore V -operation. |
| 16 | # The guarded section is here |
| 17 | $s->down; # Also known as the semaphore P -operation. |
| 18 | |
| 19 | # The default semaphore value is 1. |
| 20 | my $s = new Thread::Semaphore($initial_value); |
| 21 | $s->up($up_value); |
| 22 | $s->down($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 | =item up |
| 57 | |
| 58 | =item up NUMBER |
| 59 | |
| 60 | The C<up> method increases the semaphore's count by the number specified, |
| 61 | or by one if no number has been specified. This will unblock any thread blocked |
| 62 | trying to C<down> the semaphore if the C<up> raises the semaphore count |
| 63 | above the amount that the C<down>s are trying to decrement it by. |
| 64 | |
| 65 | =back |
| 66 | |
| 67 | =cut |
| 68 | |
| 69 | sub new { |
| 70 | my $class = shift; |
| 71 | my $val : shared = @_ ? shift : 1; |
| 72 | bless \$val, $class; |
| 73 | } |
| 74 | |
| 75 | sub down { |
| 76 | my $s = shift; |
| 77 | lock($$s); |
| 78 | my $inc = @_ ? shift : 1; |
| 79 | cond_wait $$s until $$s >= $inc; |
| 80 | $$s -= $inc; |
| 81 | } |
| 82 | |
| 83 | sub up { |
| 84 | my $s = shift; |
| 85 | lock($$s); |
| 86 | my $inc = @_ ? shift : 1; |
| 87 | ($$s += $inc) > 0 and cond_broadcast $$s; |
| 88 | } |
| 89 | |
| 90 | 1; |