1Apache::Session::Lock::USseemrapChoonrter(i3b)uted PerlADpoaccuhmee:n:tSaetsisoinon::Lock::Semaphore(3)
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NAME

6       Apache::Session::Lock::Semaphore - Provides mutual exclusion through
7       semaphores
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SYNOPSIS

10        use Apache::Session::Lock::Semaphore;
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12        my $locker = Apache::Session::Lock::Semaphore->new;
13        die "no semaphores" unless $locker;
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15        $locker->acquire_read_lock($ref);
16        $locker->acquire_write_lock($ref);
17        $locker->release_read_lock($ref);
18        $locker->release_write_lock($ref);
19        $locker->release_all_locks($ref);
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DESCRIPTION

22       Apache::Session::Lock::semaphore fulfills the locking interface of
23       Apache::Session.  Mutual exclusion is achieved through system
24       semaphores and the IPC::Semaphore module.
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CONFIGURATION

27       The module must know how many semaphores to use, and what semaphore key
28       to use. The number of semaphores has an impact on performance.  More
29       semaphores means less lock contention. You should use the maximum
30       number of semaphores that your platform will allow. On stock NetBSD,
31       OpenBSD, and Solaris systems, this is probably 16. On Linux 2.2, this
32       is 32. This module tries to guess the number based on your operating
33       system, but it is safer to configure it yourself.
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35       To set the number of semaphores, you need to pass an argument in the
36       usual Apache::Session style. The name of the argument is NSems, and the
37       value is an integer power of 2. For example:
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39        tie %s, 'Apache::Session::Blah', $id, {NSems => 16};
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41       You may also need to configure the semaphore key that this package
42       uses. By default, it uses key 31818.  You can change this using the
43       argument SemaphoreKey:
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45        tie %s, 'Apache::Session::Blah', $id, {NSems => 16, SemaphoreKey => 42};
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PROBLEMS

48       There are a few problems that people frequently encounter when using
49       this package.
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51       If you get an invalid argument message, that usually means that the
52       system is unhappy with the number of semaphores that you requested.
53       Try decreasing the number of semaphores.  The semaphore blocks that
54       this package creates are persistent until the system is rebooted, so if
55       you request 8 semaphores one time and 16 semaphores the next, it won't
56       work.  Use the system commands ipcs and ipcrm to inspect and remove
57       unwanted semphore blocks.
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59   Cygwin
60       IPC on Cygwin requires running cygserver. Without it, program will exit
61       with "Bad System call" message. It cannot be intercepted with eval.
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63       Read /usr/share/doc/Cygwin/cygserver.README for more information.
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65   Darwin/MacOS X
66       Darwin and MacOS X may not have semaphores, see
67       <http://sysnet.ucsd.edu/~bellardo/darwin/sysvsem.html>
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69   *BSD
70       Error "No space left on device" means that maximum number of semaphores
71       is reached.  See
72       <http://www.postgresql.org/docs/7.3/static/kernel-resources.html> for
73       more information.
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AUTHOR

76       This module was written by Jeffrey William Baker <jwbaker@acm.org>.
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SEE ALSO

79       Apache::Session
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83perl v5.34.0                      2022-01-20Apache::Session::Lock::Semaphore(3)
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