CONTENTS

• NAME
• VERSION
• SYNOPSIS
• DESCRIPTION
• METHODS
• NOTES
• SEE ALSO
• MAINTAINER
• LICENSE

#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 downing 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)