coro::semaphore(3pm) [debian man page]

Semaphore(3pm)						User Contributed Perl Documentation					    Semaphore(3pm)

NAME

       Coro::Semaphore - counting semaphores

SYNOPSIS

	use Coro;

	$sig = new Coro::Semaphore [initial value];

	$sig->down; # wait for signal

	# ... some other "thread"

	$sig->up;

DESCRIPTION

       This module implements counting semaphores. You can initialize a mutex with any level of parallel users, that is, you can intialize a
       sempahore that can be "down"ed more than once until it blocks. There is no owner associated with semaphores, so one thread can "down" it
       while another can "up" it.

       Counting semaphores are typically used to coordinate access to resources, with the semaphore count initialized to the number of free
       resources. Threads then increment the count when resources are added and decrement the count when resources are removed.

       You don't have to load "Coro::Semaphore" manually, it will be loaded automatically when you "use Coro" and call the "new" constructor.

       new [inital count]
	   Creates a new sempahore object with the given initial lock count. The default lock count is 1, which means it is unlocked by default.
	   Zero (or negative values) are also allowed, in which case the semaphore is locked by default.

       $sem->count
	   Returns the current semaphore count.

       $sem->adjust ($diff)
	   Atomically adds the amount given to the current semaphore count. If the count becomes positive, wakes up any waiters. Does not block if
	   the count becomes negative, however.

       $sem->down
	   Decrement the counter, therefore "locking" the semaphore. This method waits until the semaphore is available if the counter is zero.

       $sem->wait
	   Similar to "down", but does not actually decrement the counter. Instead, when this function returns, a following call to "down" or
	   "try" is guaranteed to succeed without blocking, until the next thread switch ("cede" etc.).

	   Note that using "wait" is much less efficient than using "down", so try to prefer "down" whenever possible.

       $sem->wait ($callback)
	   If you pass a callback argument to "wait", it will not wait, but immediately return. The callback will be called as soon as the
	   semaphore becomes available (which might be instantly), and gets passed the semaphore as first argument.

	   The callback might "down" the semaphore exactly once, might wake up other threads, but is NOT allowed to block (switch to other
	   threads).

       $sem->up
	   Unlock the semaphore again.

       $sem->try
	   Try to "down" the semaphore. Returns true when this was possible, otherwise return false and leave the semaphore unchanged.

       $sem->waiters
	   In scalar context, returns the number of threads waiting for this semaphore.

       $guard = $sem->guard
	   This method calls "down" and then creates a guard object. When the guard object is destroyed it automatically calls "up".

AUTHOR

	Marc Lehmann <schmorp@schmorp.de>
	http://home.schmorp.de/

perl v5.14.2							    2012-04-13							    Semaphore(3pm)

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

NAME

       Thread::Semaphore - Thread-safe semaphores

VERSION

       This document describes Thread::Semaphore version 2.12

SYNOPSIS

	   use Thread::Semaphore;
	   my $s = Thread::Semaphore->new();
	   $s->down();	 # Also known as the semaphore P operation.
	   # The guarded section is here
	   $s->up();	 # Also known as the semaphore V operation.

	   # Decrement the semaphore only if it would immediately succeed.
	   if ($s->down_nb()) {
	       # The guarded section is here
	       $s->up();
	   }

	   # Forcefully decrement the semaphore even if its count goes below 0.
	   $s->down_force();

	   # The default value for semaphore operations is 1
	   my $s = Thread::Semaphore->new($initial_value);
	   $s->down($down_value);
	   $s->up($up_value);
	   if ($s->down_nb($down_value)) {
	       ...
	       $s->up($up_value);
	   }
	   $s->down_force($down_value);

DESCRIPTION

       Semaphores provide a mechanism to regulate access to resources.	Unlike locks, semaphores aren't tied to particular scalars, and so may be
       used to control access to anything you care to use them for.

       Semaphores don't limit their values to zero and one, so they can be used to control access to some resource that there may be more than one
       of (e.g., filehandles).	Increment and decrement amounts aren't fixed at one either, so threads can reserve or return multiple resources at
       once.

METHODS

       ->new()
       ->new(NUMBER)
	       "new" creates a new semaphore, and initializes its count to the specified number (which must be an integer).  If no number is
	       specified, the semaphore's count defaults to 1.

       ->down()
       ->down(NUMBER)
	       The "down" method decreases the semaphore's count by the specified number (which must be an integer >= 1), or by one if no number
	       is specified.

	       If the semaphore's count would drop below zero, this method will block until such time as the semaphore's count is greater than or
	       equal to the amount you're "down"ing the semaphore's count by.

	       This is the semaphore "P operation" (the name derives from the Dutch word "pak", which means "capture" -- the semaphore operations
	       were named by the late Dijkstra, who was Dutch).

       ->down_nb()
       ->down_nb(NUMBER)
	       The "down_nb" method attempts to decrease the semaphore's count by the specified number (which must be an integer >= 1), or by one
	       if no number is specified.

	       If the semaphore's count would drop below zero, this method will return false, and the semaphore's count remains unchanged.
	       Otherwise, the semaphore's count is decremented and this method returns true.

       ->down_force()
       ->down_force(NUMBER)
	       The "down_force" method decreases the semaphore's count by the specified number (which must be an integer >= 1), or by one if no
	       number is specified.  This method does not block, and may cause the semaphore's count to drop below zero.

       ->up()
       ->up(NUMBER)
	       The "up" method increases the semaphore's count by the number specified (which must be an integer >= 1), or by one if no number is
	       specified.

	       This will unblock any thread that is blocked trying to "down" the semaphore if the "up" raises the semaphore's count above the
	       amount that the "down" is trying to decrement it by.  For example, if three threads are blocked trying to "down" a semaphore by
	       one, and another thread "up"s the semaphore by two, then two of the blocked threads (which two is indeterminate) will become
	       unblocked.

	       This is the semaphore "V operation" (the name derives from the Dutch word "vrij", which means "release").

NOTES

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

SEE ALSO

       Thread::Semaphore Discussion Forum on CPAN: <http://www.cpanforum.com/dist/Thread-Semaphore>

       threads, threads::shared

MAINTAINER

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

LICENSE

       This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

perl v5.18.2							    2013-11-04						    Thread::Semaphore(3pm)