Thread::Semaphore - man - phpMan

NAME
    Thread::Semaphore - Thread-safe semaphores

VERSION
    This document describes Thread::Semaphore version 2.13

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.

    ->down_timed(TIMEOUT)
    ->down_timed(TIMEOUT, NUMBER)
            The "down_timed" method attempts to decrease the semaphore's
            count by 1 or by the specified number within the specified
            timeout period given in seconds (which must be an integer >= 0).

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

            If the timeout is reached, this method will return *false*, and
            the semaphore's count remains unchanged. Otherwise, the
            semaphore's count is decremented and this method returns *true*.

    ->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 on MetaCPAN:
    <https://metacpan.org/release/Thread-Semaphore>

    Code repository for CPAN distribution:
    <https://github.com/Dual-Life/Thread-Semaphore>

    threads, threads::shared

    Sample code in the *examples* directory of this distribution on CPAN.

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.