Provided by: libprefork-perl_1.05-2_all 
NAME
prefork - Optimized module loading for forking or non-forking processes
SYNOPSIS
In a module that normally delays module loading with require
# Module Foo::Bar only uses This::That 25% of the time.
# We want to preload in in forking scenarios (like mod_perl), but
# we want to delay loading in non-forking scenarios (like CGI)
use prefork 'This::That';
sub do_something {
my $arg = shift;
# Load the module at run-time as normal
if ( $special_case ) {
require This::That;
This::That::blah(@_);
}
}
# Register a module to be loaded before forking directly
prefork::prefork('Module::Name');
In a script or module that is going to be forking.
package Module::Forker;
# Enable forking mode
use prefork ':enable';
# Or call it directly
prefork::enable();
In a third-party run-time loader
package Runtime::Loader;
use prefork ();
prefork::notify( \&load_everything );
...
sub load_everything { ... }
1;
INTRODUCTION
The task of optimizing module loading in Perl tends to move in two different directions, depending on the
context.
In a procedural context, such as scripts and CGI-type situations, you can improve the load times and
memory usage by loading a module at run-time, only once you are sure you will need it.
In the other common load profile for perl applications, the application will start up and then fork off
various worker processes. To take full advantage of memory copy-on-write features, the application should
load as many modules as possible before forking to prevent them consuming memory in multiple worker
processes.
Unfortunately, the strategies used to optimise for these two load profiles are diametrically opposed.
What improves a situation for one tends to make life worse for the other.
DESCRIPTION
The "prefork" pragma is intended to allow module writers to optimise module loading for both scenarios
with as little additional code as possible.
prefork.pm is intended to serve as a central and optional marshalling point for state detection (are we
running in compile-time or run-time mode) and to act as a relatively light-weight module loader.
Loaders and Forkers
"prefork" is intended to be used in two different ways.
The first is by a module that wants to indicate that another module should be loaded before forking. This
is known as a "Loader".
The other is a script or module that will be initiating the forking. It will tell prefork.pm that it is
either going to fork, or is about to fork, or for some other reason all modules previously mentioned by
the Loaders should be loaded immediately.
Usage as a Pragma
A Loader can register a module to be loaded using the following
use prefork 'My::Module';
The same thing can be done in such a way as to not require prefork being installed, but taking advantage
of it if it is.
eval "use prefork 'My::Module';";
A Forker can indicate that it will be forking with the following
use prefork ':enable';
In any use of "prefork" as a pragma, you can only pass a single value as argument. Any additional
arguments will be ignored. (This may throw an error in future versions).
Compatibility with mod_perl and others
Part of the design of "prefork", and its minimalistic nature, is that it is intended to work easily with
existing modules, needing only small changes.
For example, "prefork" itself will detect the $ENV{MOD_PERL} environment variable and automatically start
in forking mode.
prefork has support for integrating with third-party modules, such as Class::Autouse. The "notify"
function allows these run-time loaders to register callbacks, to be called once prefork enters forking
mode.
The synopsis entry above describes adding support for prefork.pm as a dependency. To allow your third-
party module loader without a dependency and only if it is installed use the following:
eval { require prefork; }
prefork::notify( \&function ) unless $@;
Using prefork.pm
From the Loader side, it is fairly simple. prefork becomes a dependency for your module, and you use it
as a pragma as documented above.
For the Forker, you have two options. Use as a dependency or optional use.
In the dependency case, you add prefork as a dependency and use it as a pragma with the ':enable' option.
To add only optional support for prefork, without requiring it to be installed, you should wait until the
moment just before you fork and then call "prefork::enable" directly ONLY if it is loaded.
# Load modules if any use the prefork pragma.
prefork::enable() if $INC{prefork.pm};
This will cause the modules to be loaded ONLY if there are any modules that need to be loaded. The main
advantage of the dependency version is that you only need to enable the module once, and not before each
fork.
If you wish to have your own module leverage off the forking-detection that prefork provides, you can
also do the following.
use prefork;
if ( $prefork::FORKING ) {
# Complete some preparation task
}
Modules that are prefork-aware
mod_perl/mod_perl2
Class::Autouse
FUNCTIONS
prefork $module
The 'prefork' function indicates that a module should be loaded before the process will fork. If already
in forking mode the module will be loaded immediately.
Otherwise it will be added to a queue to be loaded later if it receives instructions that it is going to
be forking.
Returns true on success, or dies on error.
enable
The "enable" function indicates to the prefork module that the process is going to fork, possibly
immediately.
When called, prefork.pm will immediately load all outstanding modules, and will set a flag so that any
further 'prefork' calls will load the module at that time.
Returns true, dying as normal is there is a problem loading a module.
notify &function
The "notify" function is used to integrate support for modules other than prefork.pm itself.
A module loader calls the notify function, passing it a reference to a "CODE" reference (either anon or a
function reference). "prefork" will store this CODE reference, and execute it immediately as soon as it
knows it is in forking-mode, but after it loads its own modules.
Callbacks are called in the order they are registered.
Normally, this will happen as soon as the "enable" function is called.
However, you should be aware that if prefork is already in preforking mode at the time that the notify
function is called, prefork.pm will execute the function immediately.
This means that any third party module loader should be fully loaded and initialised before the callback
is provided to "notify".
Returns true if the function is stored, or dies if not passed a "CODE" reference, or the callback is
already set in the notify queue.
TO DO
- Add checks for more pre-forking situations
SUPPORT
Bugs should be always submitted via the CPAN bug tracker, located at
<http://rt.cpan.org/NoAuth/ReportBug.html?Queue=prefork>
For other issues, or commercial enhancement or support, contact the author.
AUTHOR
Adam Kennedy <adamk@cpan.org>
COPYRIGHT
Thank you to Phase N Australia (<http://phase-n.com/>) for permitting the open sourcing and release of
this distribution.
Copyright 2004 - 2009 Adam Kennedy.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl
itself.
The full text of the license can be found in the LICENSE file included with this module.
perl v5.36.0 2022-12-12 prefork(3pm)