Thread::Semaphore(3pm)

1Thread::Semaphore(3pm) Perl Programmers Reference Guide Thread::Semaphore(3pm)
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NAME

6       Thread::Semaphore - Thread-safe semaphores
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VERSION

9       This document describes Thread::Semaphore version 2.09
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SYNOPSIS

12           use Thread::Semaphore;
13           my $s = Thread::Semaphore->new();
14           $s->down();   # Also known as the semaphore P operation.
15           # The guarded section is here
16           $s->up();     # Also known as the semaphore V operation.
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18           # The default semaphore value is 1
19           my $s = Thread::Semaphore-new($initial_value);
20           $s->down($down_value);
21           $s->up($up_value);
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DESCRIPTION

24       Semaphores provide a mechanism to regulate access to resources.  Unlike
25       locks, semaphores aren't tied to particular scalars, and so may be used
26       to control access to anything you care to use them for.
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28       Semaphores don't limit their values to zero and one, so they can be
29       used to control access to some resource that there may be more than one
30       of (e.g., filehandles).  Increment and decrement amounts aren't fixed
31       at one either, so threads can reserve or return multiple resources at
32       once.
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METHODS

35       ->new()
36       ->new(NUMBER)
37               "new" creates a new semaphore, and initializes its count to the
38               specified number (which must be an integer).  If no number is
39               specified, the semaphore's count defaults to 1.
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41       ->down()
42       ->down(NUMBER)
43               The "down" method decreases the semaphore's count by the
44               specified number (which must be an integer >= 1), or by one if
45               no number is specified.
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47               If the semaphore's count would drop below zero, this method
48               will block until such time as the semaphore's count is greater
49               than or equal to the amount you're "down"ing the semaphore's
50               count by.
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52               This is the semaphore "P operation" (the name derives from the
53               Dutch word "pak", which means "capture" -- the semaphore
54               operations were named by the late Dijkstra, who was Dutch).
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56       ->up()
57       ->up(NUMBER)
58               The "up" method increases the semaphore's count by the number
59               specified (which must be an integer >= 1), or by one if no
60               number is specified.
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62               This will unblock any thread that is blocked trying to "down"
63               the semaphore if the "up" raises the semaphore's count above
64               the amount that the "down" is trying to decrement it by.  For
65               example, if three threads are blocked trying to "down" a
66               semaphore by one, and another thread "up"s the semaphore by
67               two, then two of the blocked threads (which two is
68               indeterminate) will become unblocked.
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70               This is the semaphore "V operation" (the name derives from the
71               Dutch word "vrij", which means "release").
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NOTES

74       Semaphores created by Thread::Semaphore can be used in both threaded
75       and non-threaded applications.  This allows you to write modules and
76       packages that potentially make use of semaphores, and that will
77       function in either environment.
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MAINTAINER

95       Jerry D. Hedden, <jdhedden AT cpan DOT org>
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LICENSE

98       This program is free software; you can redistribute it and/or modify it
99       under the same terms as Perl itself.
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103perl v5.12.4                      2011-06-07            Thread::Semaphore(3pm)