On Thu, Dec 12, 2013 at 1:08 AM, marcinmltd <marcinm...@gmail.com> wrote: > Adding subject to the message. > Hello, > > I'm big fan of multiprocessing module, but recently I started looking at > threading in Python more closely and got couple of questions I hope You can > help me with: > > 1. When I run two or more threads in my python process are they really run > concurrently on mulicore machine?
No. The GIL allows the Python interpreter to run in only thread at a time. > 2. Browsing through documentation it looks like python interpreter protects > its sensitive states by using GIL. Can you guys list situations when this > happens? Any time Python code is being run, the GIL is held. C extensions have the option to release the GIL for long-running operations (e.g. waiting on a network socket), but they are not permitted to work with Python objects while the GIL is released. > 2. What would be general advice from python experts on when to use threadng > and when switch to multliprocessing in python? Is the decision still > influenced by how often we need to comunicate between the tasks as it's in > C\C++? Generally speaking, use threading for programs that are IO-bound (where there would be little concurrency anyway) and multiprocessing for programs that are CPU-bound. Communication between processes is more expensive than communication between threads, so that could be an important criterion. -- https://mail.python.org/mailman/listinfo/python-list
