Session::Lock::SemaphoUserpContributed Perl DocumSession::Lock::Semaphore(3pm)

NAME
       Apache::Session::Lock::Semaphore - Provides mutual exclusion through
       sempahores

SYNOPSIS
        use Apache::Session::Lock::Semaphore;

        my $locker = new Apache::Session::Lock::Semaphore;

        $locker->acquire_read_lock($ref);
        $locker->acquire_write_lock($ref);
        $locker->release_read_lock($ref);
        $locker->release_write_lock($ref);
        $locker->release_all_locks($ref);

DESCRIPTION
       Apache::Session::Lock::Sempahore fulfills the locking interface of
       Apache::Session.  Mutual exclusion is achieved through system
       semaphores and the IPC::Semaphore module.

CONFIGURATION
       The module must know how many semaphores to use, and what semaphore key
       to use.  The number of semaphores has an impact on performance.  More
       semaphores meansless lock contention.  You should use the maximum num-
       ber of sempahores that your platform will allow.  On stock NetBSD,
       OpenBSD, and Solaris systems, this is probably 16.  On Linux 2.2, this
       is 32.  This module tries to guess the number based on your operating
       system, but it is safer to configure it yourself.

       To set the number of semaphores, you need to pass an argument in the
       usual Apache::Session style.  The name of the argument is NSems, and
       the value is an integer power of 2.  For example:

        tie %s, 'Apache::Session::Blah', $id, {NSems => 16};

       You may also need to configure the semaphore key that this package
       uses.  By default, it uses key 31818.  You can change this using the
       argument SemaphoreKey:

        tie %s, 'Apache::Session::Blah', $id, {NSems => 16, SemaphoreKey => 42};

PROBLEMS
       There are a few problems that people frequently encounter when using
       this package.

       If you get an invalid argument message, that usually means that the
       system is unhappy with the number of semaphores that you requested.
       Try decreasing the number of semaphores.  The semaphore blocks that
       this package creates are persistent until the system is rebooted, so if
       you request 8 sempahores one time and 16 sempahores the next, it won't
       work.  Use the system commands ipcs and ipcrm to inspect and remove
       unwanted semphore blocks.

AUTHOR
       This module was written by Jeffrey William Baker <jwbaker@acm.org>.

SEE ALSO
       Apache::Session

perl v5.8.8                       2004-10-09     Session::Lock::Semaphore(3pm)