NAME

Thread::Queue::Any::Monitored - monitor a queue for any specific content

SYNOPSIS

    use Thread::Queue::Any::Monitored;
    my ( $q, $t ) = Thread::Queue::Any::Monitored->new( {
      monitor => sub { print "monitoring value $_[0]\n" }, # is a must
      pre     => sub { print "prepare monitoring\n" },     # optional
      post    => sub { print "stop monitoring\n" },        # optional
      queue   => $queue, # use existing queue, create new if not specified
      exit    => 'exit', # default to undef
    } );

    $q->enqueue( "foo", ['listref'], {'hashref'} );
    $q->enqueue(undef); # exit value by default

    @post= $t->join; # optional, wait for monitor thread to end

    $queue= Thread::Queue::Any::Monitored->self; # "pre", "do", "post"

VERSION

This documentation describes version 0.13.

DESCRIPTION

                    *** A note of CAUTION ***

 This module only functions on threaded perl or an unthreaded perl
 with the "forks" module installed.

 Please also note that this documentation describes the "maint" version
 of this code.  This version is essentially frozen.  Please use a 5.14
 or higher version of perl for the "blead" version of this code.

                    *************************

A queue, as implemented by Thread::Queue::Any::Monitored is a thread-safe data structure that inherits from Thread::Queue::Any. But unlike the standard Thread::Queue::Any, it starts a single thread that monitors the contents of the queue by taking new sets of values off the queue as they become available.

It can be used for simply logging actions that are placed on the queue. Or only output warnings if a certain value is encountered. Or whatever.

The action performed in the thread, is determined by a name or reference to a subroutine. This subroutine is called for every set of values obtained from the queue.

Any number of threads can safely add sets of values to the end of the list.

CLASS METHODS

new

 ( $queue, $thread )= Thread::Queue::Any::Monitored->new( {
   pre     => \&pre,
   monitor => 'monitor',
   post    => \&module::post,
   queue   => $queue, # use existing queue, create new if not specified
   exit    => 'exit', # default to undef
 } );

The new function creates a monitoring function on an existing or on an new (empty) queue. It returns the instantiated Thread::Queue::Any::Monitored object in scalar context: in that case, the monitoring thread will be detached and will continue until the exit value is passed on to the queue. In list context, the thread object is also returned, which can be used to wait for the thread to be really finished using the join() method.

The first input parameter is a reference to a hash that should at least contain the "monitor" key with a subroutine reference.

The other input parameters are optional. If specified, they are passed to the the "pre" routine which is executed once when the monitoring is started.

The following field must be specified in the hash reference:

do

 monitor => 'monitor_the_queue',        # assume caller's namespace

or:

 monitor => 'Package::monitor_the_queue',

or:

 monitor => \&SomeOther::monitor_the_queue,

or:

 monitor => sub { print "anonymous sub monitoring the queue\n" },

The "monitor" field specifies the subroutine to be executed for each set of values that is removed from the queue. It must be specified as either the name of a subroutine or as a reference to a (anonymous) subroutine.

The specified subroutine should expect the following parameters to be passed:

 1..N  set of values obtained from the queue

What the subroutine does with the values, is entirely up to the developer.

The following fields are optional in the hash reference:

pre

 pre => 'prepare_monitoring',           # assume caller's namespace

or:

 pre => 'Package::prepare_monitoring',

or:

 pre => \&SomeOther::prepare_monitoring,

or:

 pre => sub { print "anonymous sub preparing the monitoring\n" },

The "pre" field specifies the subroutine to be executed once when the monitoring of the queue is started. It must be specified as either the name of a subroutine or as a reference to a (anonymous) subroutine.

The specified subroutine should expect the following parameters to be passed:

 1..N  any extra parameters that were passed with the call to L<new>.

post

 post => 'stop_monitoring',             # assume caller's namespace

or:

 post => 'Package::stop_monitoring',

or:

 post => \&SomeOther::stop_monitoring,

or:

 post => sub { print "anonymous sub when stopping the monitoring\n" },

The "post" field specifies the subroutine to be executed once when the monitoring of the queue is stopped. It must be specified as either the name of a subroutine or as a reference to a (anonymous) subroutine.

The specified subroutine should expect the following parameters to be passed:

 1..N  any parameters that were passed with the call to L<new>.

Any values returned by the "post" routine, can be obtained with the join method on the thread object.

queue

 queue => $queue,  # create new one if not specified

The "queue" field specifies the Thread::Queue::Any object that should be monitored. A new Thread::Queue::Any object will be created if it is not specified.

exit

 exit => 'exit',   # default to undef

The "exit" field specifies the value that will cause the monitoring thread to seize monitoring. The "undef" value will be assumed if it is not specified. This value should be enqueued to have the monitoring thread stop.

self

 $queue= Thread::Queue::Any::Monitored->self; # only within "pre" and "do"

The class method "self" returns the object for which this thread is monitoring. It is available within the "pre" and "do" subroutine only.

OBJECT METHODS

enqueue

 $queue->enqueue( $scalar, [], {} );
 $queue->enqueue('exit'); # stop monitoring

The enqueue method adds all specified parameters as a set on to the end of the queue. The queue will grow as needed to accommodate the list. If the "exit" value is passed, then the monitoring thread will shut itself down.

REQUIRED MODULES

 Thread::Queue::Any (0.16)
 Thread::Queue::Monitored (0.14)

CAVEATS

You cannot remove any values from the queue, as that is done by the monitoring thread. Therefore, the methods "dequeue", "dequeue_dontwait" and "dequeue_keep" are disabled on this object.

Passing unshared values between threads is accomplished by serializing the specified values using Storable when enqueuing and de-serializing the queued value on dequeuing. This allows for great flexibility at the expense of more CPU usage. It also limits what can be passed, as e.g. code references can not be serialized and therefore not be passed.

AUTHOR

Elizabeth Mattijsen, <liz@dijkmat.nl>.

Please report bugs to <perlbugs@dijkmat.nl>.

COPYRIGHT

Copyright (c) 2002, 2003, 2007, 2012 Elizabeth Mattijsen <liz@dijkmat.nl>. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

SEE ALSO

threads, threads::shared, Thread::Queue::Any, Storable.

cpanm Thread::Queue::Any::Monitored

perl -MCPAN -e shell
install Thread::Queue::Any::Monitored