package Thread::Queue::Monitored;
# initializations
@ISA= qw(Thread::Queue);
$VERSION= '0.14';
# be as strict as possible
use strict;
# modules that we need
use Thread::Queue (); # no need to pollute namespace
# self referencing within monitoring thread
my $SELF;
# satisfy -require-
1;
#-------------------------------------------------------------------------------
# new
#
# Create a monitored queue
#
# IN: 1 class to bless with
# 2 reference/name of subroutine doing the monitoring
# 3 value to consider end of monitoring action (default: undef)
# OUT: 1 instantiated object
# 2 (optional) thread object of monitoring thread
sub new {
my $class= shift;
my $param= shift;
# sanity check
my $monitor= $param->{monitor};
die "Must specify a subroutine to monitor the queue" if !$monitor;
# make sure it is a code ref
my $namespace= caller() . '::';
$monitor= _makecoderef( $namespace, $monitor ) if !ref($monitor);
# get pre and post code
my $pre= $param->{pre};
$pre= _makecoderef( $namespace, $pre ) if $pre and !ref($pre);
my $post= $param->{post};
$post= _makecoderef( $namespace, $post ) if $post and !ref($post);
# obtain the queue object
my $self= $param->{queue}
? bless $param->{queue}, $class
: $class->SUPER::new;
# create the thread
no strict 'refs';
my $thread= threads->new(
\&{ $class . '::_monitor' },
$self,
wantarray,
$monitor,
$param->{exit}, # don't care if not available: then undef = exit value
$post,
$pre,
@_,
);
return wantarray ? ($self,$thread) : $self;
} #new
#-------------------------------------------------------------------------------
# self
#
# return singleton
#
# IN: 1 class (ignored)
# OUT: 1 instantiated queue object
sub self { $SELF } #self
#-------------------------------------------------------------------------------
# dequeue
#
# not allowed to do this
#
# IN: 1 instantiated object (ignored)
# OUT: 1 dequeued value (not returned)
sub dequeue { _die() } #dequeue
#-------------------------------------------------------------------------------
# dequeue_dontwait
#
# not allowed to do this
#
# IN: 1 instantiated object (ignored)
# OUT: 1 dequeued value (not returned)
sub dequeue_dontwait { _die() } #dequeue_dontwait
#-------------------------------------------------------------------------------
# dequeue_nb
#
# not allowed to do this
#
# IN: 1 instantiated object (ignored)
# OUT: 1 dequeued value (not returned)
sub dequeue_nb { _die() } #dequeue_nb
#-------------------------------------------------------------------------------
# dequeue_keep
#
# not allowed to do this
#
# IN: 1 instantiated object (ignored)
# OUT: 1 dequeued value (not returned)
sub dequeue_keep { _die() } # dequeue_keep
#-------------------------------------------------------------------------------
#
# Internal subroutines
#
#-------------------------------------------------------------------------------
# _die
#
# die as if in caller
#
# IN: 1 instantiated object (ignored)
sub _die {
( my $caller= ( caller(1) )[3] ) =~ s#^.*::##;
die "You cannot '$caller' on a monitored queue";
} #_die
#-------------------------------------------------------------------------------
# _makecoderef
#
# Return coderef for given namespace / sub
#
# IN: 1 namespace prefix
# 2 subroutine name
# OUT: 1 code reference
sub _makecoderef {
my ( $namespace, $code )= @_;
# ensure fully qualified
$code= $namespace.$code if $code !~ m#::#;
return \&{$code};
} #_makecoderef
#-------------------------------------------------------------------------------
# _monitor
#
# monitor a queue
#
# IN: 1 queue object to monitor
# 2 flag: to keep thread attached
# 3 code reference of monitoring routine
# 4 exit value
# 5 code reference of preparing routine (if available)
# 6..N parameters passed to creation routine
sub _monitor {
my $queue= $SELF= shift;
threads->self->detach if !shift;
my $monitor= shift;
my $exit= shift;
# get pre/post processing
my $post= shift || sub {};
my $pre= shift;
$pre->( @_ ) if $pre;
# processing
my @value;
while (1) {
# get all values from the queue
{
lock( @{$queue} );
threads::shared::cond_wait @{$queue} until @{$queue};
@value= @{$queue};
@{$queue} = ();
}
# process all values
foreach (@value) {
# done, was we've seen the exit value
if ( defined($exit) ) {
return $post->(@_) if $_ eq $exit;
}
# no value, so we're done
elsif( !defined($_) ) {
return $post->(@_);
}
# perform the monitoring for this value
$monitor->($_);
}
}
} #_monitor
#-------------------------------------------------------------------------------
__END__
=head1 NAME
Thread::Queue::Monitored - monitor a queue for specific content
=head1 SYNOPSIS
use Thread::Queue::Monitored;
my ($q,$t) = Thread::Queue::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");
$q->enqueue(undef); # exit value by default
@post= $t->join; # optional, wait for monitor thread to end
$queue= Thread::Queue::Monitored->self; # "pre", "do", "post" only
=head1 VERSION
This documentation describes version 0.14.
=head1 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
version of perl for the "blead" version of this code.
*************************
A queue, as implemented by C<Thread::Queue::Monitored> is a thread-safe
data structure that inherits from C<Thread::Queue>. But unlike the
standard C<Thread::Queue>, it starts a single thread that monitors the
contents of the queue by taking new 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 value obtained from
the queue.
Any number of threads can safely add elements to the end of the list.
=head1 CLASS METHODS
=head2 new
( $queue, $thread )= Thread::Queue::Monitored->new( {
pre => \&pre,
monitor => 'monitor',
post => 'module::done',
queue => $queue, # use existing queue, create new if not specified
exit => 'exit', # default to undef
} );
The C<new> function creates a monitoring function on an existing or on an new
(empty) queue. It returns the instantiated Thread::Queue::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 C<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 B<must> be specified in the hash reference:
=over 2
=item 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 value
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 parameter to be passed:
1 value obtain from the queue
What the subroutine does with the value, is entirely up to the developer.
=back
The following fields are B<optional> in the hash reference:
=over 2
=item 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 parameters that were passed with the call to L<new>.
=item 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 C<join>
method on the thread object.
=item queue
queue => $queue, # create new one if not specified
The "queue" field specifies the Thread::Queue object that should be monitored.
A new L<Thread::Queue> object will be created if it is not specified.
=item 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 L<enqueue>d to have the monitoring thread stop.
=back
=head2 self
$queue = Thread::Queue::Monitored->self; # only "pre", "do" and "post"
The class method "self" returns the object for which this thread is
monitoring. It is available within the "pre", "do" and "post" subroutine
only.
=head1 OBJECT METHODS
=head2 enqueue
$queue->enqueue( $value1, $value2 );
$queue->enqueue( 'exit' ); # stop monitoring
The C<enqueue> method adds all specified parameters 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.
=head1 REQUIRED MODULES
Thread::Queue (any)
=head1 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.
=head1 AUTHOR
Elizabeth Mattijsen, <liz@dijkmat.nl>.
Please report bugs to <perlbugs@dijkmat.nl>.
=head1 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.
=head1 SEE ALSO
L<threads>, L<threads::shared>, L<Thread::Queue>.
=cut