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package Thread::Semaphore; |
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use Thread qw(cond_wait cond_broadcast); |
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use vars qw($VERSION); |
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$VERSION = '1.00'; |
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=head1 NAME |
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Thread::Semaphore - thread-safe semaphores (5.005-threads) |
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=head1 CAVEAT |
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This Perl installation is using the old unsupported "5.005 threads". |
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Use of the old threads model is discouraged. |
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For the whole story about the development of threads in Perl, and why |
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you should B<not> be using "old threads" unless you know what you're |
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doing, see the CAVEAT of the C<Thread> module. |
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=head1 SYNOPSIS |
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use Thread::Semaphore; |
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my $s = new Thread::Semaphore; |
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$s->up; # Also known as the semaphore V -operation. |
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# The guarded section is here |
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$s->down; # Also known as the semaphore P -operation. |
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# The default semaphore value is 1. |
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my $s = new Thread::Semaphore($initial_value); |
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$s->up($up_value); |
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$s->down($up_value); |
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=head1 DESCRIPTION |
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Semaphores provide a mechanism to regulate access to resources. Semaphores, |
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unlike locks, aren't tied to particular scalars, and so may be used to |
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control access to anything you care to use them for. |
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Semaphores don't limit their values to zero or one, so they can be used to |
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control access to some resource that may have more than one of. (For |
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example, filehandles) Increment and decrement amounts aren't fixed at one |
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either, so threads can reserve or return multiple resources at once. |
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=head1 FUNCTIONS AND METHODS |
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=over 8 |
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=item new |
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=item new NUMBER |
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C<new> creates a new semaphore, and initializes its count to the passed |
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number. If no number is passed, the semaphore's count is set to one. |
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=item down |
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=item down NUMBER |
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The C<down> method decreases the semaphore's count by the specified number, |
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or one if no number has been specified. If the semaphore's count would drop |
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below zero, this method will block until such time that the semaphore's |
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count is equal to or larger than the amount you're C<down>ing the |
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semaphore's count by. |
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=item up |
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=item up NUMBER |
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The C<up> method increases the semaphore's count by the number specified, |
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or one if no number's been specified. This will unblock any thread blocked |
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trying to C<down> the semaphore if the C<up> raises the semaphore count |
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above what the C<down>s are trying to decrement it by. |
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=back |
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=cut |
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sub new { |
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my $class = shift; |
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my $val = @_ ? shift : 1; |
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bless \$val, $class; |
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} |
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sub down : locked : method { |
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my $s = shift; |
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my $inc = @_ ? shift : 1; |
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cond_wait $s until $$s >= $inc; |
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$$s -= $inc; |
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} |
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sub up : locked : method { |
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my $s = shift; |
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my $inc = @_ ? shift : 1; |
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($$s += $inc) > 0 and cond_broadcast $s; |
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} |
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1; |
