source: trunk/essentials/dev-lang/perl/pod/perlothrtut.pod@ 3397

=head1 NAME

perlothrtut - old tutorial on threads in Perl

=head1 DESCRIPTION

B<WARNING>:
This tutorial describes the old-style thread model that was introduced in
release 5.005. This model is now deprecated, and will be removed, probably
in version 5.10. The interfaces described here were considered
experimental, and are likely to be buggy.

For information about the new interpreter threads ("ithreads") model, see
the F<perlthrtut> tutorial, and the L<threads> and L<threads::shared>
modules.

You are strongly encouraged to migrate any existing threads code to the
new model as soon as possible.

=head1 What Is A Thread Anyway?

A thread is a flow of control through a program with a single
execution point.

Sounds an awful lot like a process, doesn't it? Well, it should.
Threads are one of the pieces of a process.  Every process has at least
one thread and, up until now, every process running Perl had only one
thread.  With 5.005, though, you can create extra threads.  We're going
to show you how, when, and why.

=head1 Threaded Program Models

There are three basic ways that you can structure a threaded
program.  Which model you choose depends on what you need your program
to do.  For many non-trivial threaded programs you'll need to choose
different models for different pieces of your program.

=head2 Boss/Worker

The boss/worker model usually has one `boss' thread and one or more
`worker' threads.  The boss thread gathers or generates tasks that need
to be done, then parcels those tasks out to the appropriate worker
thread.

This model is common in GUI and server programs, where a main thread
waits for some event and then passes that event to the appropriate
worker threads for processing.  Once the event has been passed on, the
boss thread goes back to waiting for another event.

The boss thread does relatively little work.  While tasks aren't
necessarily performed faster than with any other method, it tends to
have the best user-response times.

=head2 Work Crew

In the work crew model, several threads are created that do
essentially the same thing to different pieces of data.  It closely
mirrors classical parallel processing and vector processors, where a
large array of processors do the exact same thing to many pieces of
data.

This model is particularly useful if the system running the program
will distribute multiple threads across different processors.  It can
also be useful in ray tracing or rendering engines, where the
individual threads can pass on interim results to give the user visual
feedback.

=head2 Pipeline