/ 
forks-0.01
River stage one • 5 direct dependents • 5 total dependents
/ threads

NAME

forks - drop-in replacement for Perl threads using fork()

SYNOPSIS

use forks;

my $thread = threads->new( sub {       # or ->create or async()
  print "Hello world from a thread\n";
} );

$thread->join;

threads->detach;
$thread->detach;

my $tid    = $thread->tid;
my $owntid = threads->tid;

my $self    = threads->self;
my $threadx = threads->object( $tidx );

threads->yield();

$_->join foreach threads->list;

unless (fork) {
  threads->isthread; # intended to be used in a child-init Apache handler
}

use forks qw(debug);
threads->debug( 1 );

perl -Mforks -Mforks::shared threadapplication

DESCRIPTION

The "forks" pragma allows a developer to use threads without having to have a threaded perl, or to even run 5.8.0 or higher. There were a number of goals that I am trying to reach with this implementation.

memory usage

The standard Perl 5.8.0 threads implementation is very memory consuming, which makes it basically impossible to use in a production environment, particularly with mod_perl and Apache. Because of the use of the standard Unix fork() capabilities, most operating systems will be able to use the Copy-On-Write (COW) memory sharing capabilities (whereas with the standard Perl 5.8.0 threads implementation, this is thwarted by the Perl interpreter cloning process that is used to create threads). The memory savings have been confirmed.

mod_perl / Apache

This threads implementation allows you to use a standard, pre-forking Apache server and have the children act as threads (with the class method isthread). This is as yet untested within Apache, but should work.

same API as threads

You should be able to run threaded applications unchanged by simply making sure that the "forks.pm" and "forks::shared.pm" modules are loaded, e.g. by specifying them on the command line. This doesn't work still because the : shared attribute has not yet been implemented.

development / demonstration tool

Because you do not need a threaded Perl to use forks.pm, you can start prototyping threaded applications with the Perl executable that you are used to. Just download the "forks.pm" package from CPAN and install that. So the threshold for trying out threads in Perl has become much lower. Even Perl 5.005 should in principle be able to support the forks.pm module: because of some issues with regards to the availability of XS features between different versions of Perl, it seems that 5.8.0 (unthreaded) is what you need at least.

IMPLEMENTATION

This is the very first version that I'm making public. There is still a lot to do, but the basic functionalities seem to work. The missing pieces are just a matter of programming. If you would like to participate in this, please do!

This version is mostly written in Perl. Inter-process communication is done by using sockets, with the process that stores the shared variables as the server and all the processes that function as threads, as clients.

why sockets?

The reason I chose sockets for inter-thread communication above using a shared memory library, is that a blocking socket allows you to elegantly solve the problem of a thread that is blocking for a certain event. Any polling that might occur, is not occurring at the Perl level, but at the level of the socket, which should be much better and probably very optimized already.

EXTRA CLASS METHODS

Apart from the standard class methods, the following class methods are supplied by the "forks" threads implementation.

isthread

unless (fork) {
  threads->isthread; # this process is a detached thread now
}

The "isthread" class method attempt to make a connection with the shared variables process. If it succeeds, then the process will function as a detached thread and will allow all the threads methods to operate.

This method is mainly intended to be used from within a child-init handler in a pre-forking Apache server. All the children that handle requests become threads as far as Perl is concerned, allowing you to use shared variables between all of the Apache processes.

debug

threads->debug( 1 );
$debug = threads->debug;

The "debug" class method allows you to (re)set a flag which causes extensive debugging output of the communication between threads to be output to STDERR. The format is still subject to change and therefore still undocumented.

CAVEATS

Because of the use of sockets for inter-thread communication, there is an inherent larger latency with the interaction between threads. However, the fact that sockets are used, may open up the possibility to share threads over more than one physical machine.

KNOWN PROBLEMS

These problems are known and will be fixed in the future:

test-suite exits in a weird way

Although there are no errors in the test-suite, the test harness thinks there is something wrong because of an unexpected exit() value. Not sure what to do about this yet.

CREDITS

Lars Fenneberg for helping me through the initial birthing pains.

Arthur Bergman for implementing the first working version of Perl threads support and providing us with an API to build on.

AUTHOR

Elizabeth Mattijsen, <liz@dijkmat.nl>.

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

COPYRIGHT

Copyright (c) 2002 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.