Thread::Use - use a module inside a thread only

    use Thread::Use;

    threads->new( sub {
     useit Module;
     useit Module qw(parameters);

     noit Module;
     noit Module qw(parameters);
    } );

                  *** A note of CAUTION ***

 This module only functions on Perl versions 5.8.0 and later.
 And then only when threads are enabled with -Dusethreads.  It
 is of no use with any version of Perl before 5.8.0 or without
 threads enabled.

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

When you are programming threaded applications and are interested in saving memory by selectively loading modules inside threads only, you will find that even if you use a module inside a thread, it is in fact available to all threads, including the main thread.

This is caused by the fact that use is executed at compile time. At which time Perl doesn't know anything about threads yet.

However, some modules, specifically the ones that are (partly) implemented in XS, do not (yet) survive the cloning process that is involved with creating threads. So you can only use these modules inside threads only. But if you use a module, it will be read in at compile time.

Of course, a use is nothing more than a require followed by a call to the "import" class routine (if available). But that doesn't feel natural to do. So this module allows you to use the useit (for use in threads command to indicate that a module should only be used inside a thread.

For example: suppose you only need the PerlIO::gzip module inside a thread:

 use Thread::Use;  # can be anywhere in your program

 threads->new( \&zipfile,filename,contents ); # start the thread

 sub zipfile {
   useit PerlIO::gzip;  # only use inside this thread
   open( my $out,'>:gzip', $_[0] ) or die "$_[0]: $!";
   print $out $_[1];
   close( $out );
 }

For completeness, it is also possible to pass any parameters as you would with the use command. So:

 sub storable {
   useit Storable qw(freeze); # export "freeze" to namespace of thread
   my $frozen = freeze( \@_ );
 }

or to use the opposite no equivalent;

 sub warnings {
   useit warnings "all";
   # special code
   noit warnings "all";
 }

 (none)

This modules is still experimental and subject to change. At the current stage it is more a proof of concept than anything else.

There is no way to useit a module without having it call the "import" class method, as you can do with use Module (). However, a simple require Module does exactly the same, so if you want to useit a module without calling its "import" method, you should just use require.

Elizabeth Mattijsen, <liz@dijkmat.nl>.

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

Copyright (c) 2002-2003 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.

threads.