[ANN]: "newthreading" - an approach to simplified thread usage, and a path to getting rid of the GIL

John Nagle nagle at animats.com
Fri Jun 25 20:15:02 CEST 2010

We have just released a proof-of-concept implementation of a new
approach to thread management - "newthreading".  It is available
for download at


The user's guide is at


This is a pure Python implementation of synchronized objects, along
with a set of restrictions which make programs race-condition free,
even without a Global Interpreter Lock.  The basic idea is that
classes derived from SynchronizedObject are automatically locked
at entry and unlocked at exit. They're also unlocked when a thread
blocks within the class.  So at no time can two threads be active
in such a class at one time.

In addition, only "frozen" objects can be passed in and out of
synchronized objects.  (This is somewhat like the multiprocessing
module, where you can only pass objects that can be "pickled".
But it's not as restrictive; multiple threads can access the
same synchronized object, one at a time.

This pure Python implementation is usable, but does not improve
performance.  It's a proof of concept implementation so that
programmers can try out synchronized classes and see what it's
like to work within those restrictions.

The semantics of Python don't change for single-thread programs.
But when the program forks off the first new thread, the rules
change, and some of the dynamic features of Python are disabled.

Some of the ideas are borrowed from Java, and some are from 
"safethreading".  The point is to come up with a set of liveable
restrictions which would allow getting rid of the GIL.  This
is becoming essential as Unladen Swallow starts to work and the
number of processors per machine keeps climbing.

This may in time become a Python Enhancement Proposal.  We'd like
to get some experience with it first. Try it out and report back.
The SourceForge forum for the project is the best place to report problems.

				John Nagle

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