NAME IPC::Semaphore::Set

DESCRIPTION An abstract interface to semaphore sets and their resources.

A semaphore is an abstract data type that is provided by the system to
give access control to common resources by multiple processes in
parallel programming or in a multi-user environment.

A semaphore 'set' is the set of resources the system provides by an
identification number, and the values (availability) of those resources.

Resources are the semaphores themselves in the set.

You could, for instance, use a semaphore to lock on a single file
between multiple processes by saying that the set has one resource (one
file) and that the resource has one availability (one process can use it
at one time). You could also represent a series of network printers.
Perhaps you have five printers that all have the ability to do ten jobs.
You could create the semaphore set with five resources, each resource
with ten availability.

This module tries to "Do The Right Thing". It assumes a lot about what
you're looking for when you call '->new', and basically will set you up
with a semaphore set that has at least one resource with at least one
availability. If this assumption is wrong for your purposes, pay close
attention to the options for '->new'.

SYNOPSIS Get/Create a semaphore set:

        my $semset = IPC::Semaphore::Set->new(
                key_name     => 'my_lock',
                resources    => 2,
                availability => 3,
        );

The above semaphore set has two resource, each of those resources has an
availability of three.

Now you can get the first resource (resource 0):

        my $resource = $semset->resource;

Or you can select the resource explicitly:

        my $resource = $semset->resource(1);

But note that with two resources total, one is our last resource because
we start at "0".

You can make conditionals checking whether or not a lock is available on
the resource:

        if ($semset->resource->lock) {
                # ... can use resource!
        } else {
                # ... can't use resource!
        }

You can simply wait for resource availability:

        $semset->resource->lockWait;
        # ... resource is now available

You can die if the resource isn't currently available:

        $semset->resource->lockOrDie;
        # ... if we're here we have a lock

METHODS new Get a new IPC::Semaphore::Set object. If 'key' is provided, get or create a semaphore with that key. if 'key_name' is provided, generate a key based off of the ascii character codes of that name. If neither is provided, a new 'private' semaphore set will be created (note that 'private' is how SysV refers to it, but this is something of a misnomer).

    ARGUMENTS

        key A numeric key to get/create the semaphore.

        key_name
            A "word" key to get/create the semaphore.

        value
            How much value (availability) the resources in the set
            should have. Is ignored if the semaphore existed previously,
            and is optional. Defaults to 1.

        resources
            How many resources (semaphores) will be in the set. Is
            ignored if the semaphore existed previously, and is
            optional. Defaults to 1.

        flags
            IPC::SysV flags that will be used to create the semaphore
            set.

            Defaults to the following:

                    S_IRUSR | S_IWUSR | IPC_CREAT | SEM_UNDO

            Which means it creates it if it doesn't exist, keeps track
            of ownership, and will clean up it's changes after exit.

resource
    Returns a IPC::Semaphore::Set::Resource object.

    A "resource" is an abstraction around a semaphore in a set. For
    every semaphore present in your semaphore set you will have a
    "resource" to reference that.

    ARGUMENTS

        number
            The number of the resource in the semaphore set

        semaphore
            The IPC::Semaphore object that the resource is a part of.

        key The number that represents the set.

        cleanup_object
            Boolean. If enabled the object DESTROY will revert changes
            to the resource.

            Defaults to 1.

    RESOURCE METHODS

        lock
            Attempts to get a lock on the resource and returns boolean.

        lockWait
            Waits until a lock becomes available on the resource then
            returns 1.

        lockWaitTimeout
            Takes first argument as seconds to wait for a lock, or
            defaults to 3 seconds.

            Returns boolean.

        lockWaitTimeoutDie
            Takes first arguments as seconds to wait for a lock, or
            defaults to 3 seconds.

            Dies if a lock can not be established, or returns 1.

        lockOrDie
            Attempts to get a lock on the resource and dies if it can
            not. Returns 1 otherwise.

        addValue
            Adds a single point of value to the resource

        number
            Returns the number of the resource in its semaphore set

        semaphore
            Returns the IPC::Semaphore the resource is a part of.

        value
            Returns the value of the current semaphore resource.

resources
    Returns a list or arrayref of all the IPC::Semaphore::Set::Resource
    objects available for this semaphore set.

id  Returns the numeric system ID of the semaphore set.

key Returns the numeric key if available.

keyName
    Returns the 'word' key if used.

remove
    Remove the semaphore set entirely from the system.

sem Returns the internal 'IPC::Semaphore' object.