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Bug#779481: ITP: libthread-tie-perl -- alternative separate thread implementation of shared variables

Package: wnpp
Owner: Christopher Hoskin <christopher.hoskin@gmail.com>
Severity: wishlist
X-Debbugs-CC: debian-devel@lists.debian.org,debian-perl@lists.debian.org

* Package name    : libthread-tie-perl
  Version         : 0.13
  Upstream Author : Elizabeth Mattijsen <liz@dijkmat.nl>
* URL             : https://metacpan.org/release/Thread-Tie
* License         : Artistic or GPL-1+
  Programming Lang: Perl
  Description     : alternative separate thread implementation of shared variables

The standard shared variable scheme used by Perl, is based on tie-ing the
variable to some very special dark magic. This dark magic ensures that shared
variables, which are copied just as any other variable when a thread is
started, update values in all of the threads where they exist as soon as the
value of a shared variable is changed.

The Thread::Tie module is a proof-of-concept implementation of another approach
to shared variables. Instead of having shared variables exist in all the
threads from which they are accessible, shared variable exist as "normal",
unshared variables in a seperate thread. Only a tied object exists in each
thread from which the shared variable is accesible.

Through the use of a client-server model, any thread can fetch and/or update
variables living in that thread. This client-server functionality is hidden
under the hood of tie(). So you could say that one dark magic (the current
shared variables implementation) is replaced by another dark magic.

The Thread::Tie approach has the following advantages:

* Memory usage - This implementation circumvents the memory leak that currently
  (threads::shared version 0.90) plagues any shared array or shared hash
* Tieing shared variables - Because the current implementation uses tie-ing,
  you can not tie a shared variable. The same applies for this implementation
  you might say. However, it is possible to specify a non-standard tie
  implementation for use within the thread. So with this implementation you can
  tie() a shared variable. So you could tie a shared hash to a DBM file à la
  dbmopen() with this module.

Of course there are disadvantages to this approach:

* Pure Perl implementation - This module is currently a pure Perl
  implementation. This is ok for a proof of concept, but may need re-
  implementation in pure XS or in Inline::C for production use.

* Tradeoff between cpu and memory - This implementation currently uses (much)
  more cpu than the standard shared variables implementation. Whether this
  would still be true when re-implemented in XS or Inline::C, remains to be seen.

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