[EuroPython 2012] A. Rigo, A. Cuni, M. Fijalkowski - 2 JULY 2012 in "Track Spaghetti"
In the first part of the keynote we will present the current status of PyPy, with a particular focus on what happened in the last year. We will give a brief overview of the current speed and the on-going development efforts. The second part of the keynote is about one particular feature whose development is in progress in PyPy: Automatic Mutual Exclusion. What it is needs some explanation: The GIL, or Global Interpreter Lock, is a well-known issue for Python programmers that want to have a single program using the multiple cores of today’s machines. This keynote is not about writing a GIL-less Python interpreter; although hard, this has been done before, notably in Jython. The real issue is that writing each and every multi-threaded Python programs is hard too. The threading module offers locks in several variants, conditions, events, semaphores… But using them correctly without missing one case is difficult, impossible to seriously test, often impossible to retrofit into existing programs, and arguably doesn’t scale. (Other solutions like the multiprocessing module are at best workarounds, suffering some of the same issues plus their own ones.) Instead, this keynote is about an alternate solution: a minimal thread-less API that lets programs use multiple cores, without worrying about races. This may sound impossible, but is in fact similar to the API simplification of using a garbage collected language over an explicitly managed one — what is not minimal is “just” the internal implementation of that API. I will explain how it can actually be done using Automatic Mutual Exclusion, a technique based on Transactional Memory. I will give preliminary results on a modified version of the PyPy Python interpreter that show that it can actually work. I will also explain how the API is used, e.g. in a modified Twisted reactor that gives multi-core capability to any existing, non-thread-based Twisted program.