I have followed the GIL debate in python for some time. I don't want to get into the regular debate about if it should be gotten rid of (though I am curious about the status of that for Python 3)... personally I think I can do multi-threaded programming well, but I also see the benefits of a multiprocess approach. I'm not so egotistical that I don't realize perhaps my mt programming has not been "right" (though it worked and was debuggable) or more likely that doing it right I have avoided even trying some things people want mt programming to do... i.e. to do mt programming right you start to use queues a lot, inter-thread asynchronous, non-blocking, communication, which is essentially the multi-process approach, using IPC (except that the threads can see the same memory when, in your special case, you know that's ok. Given something like a reader-writer lock, this can have benefits... but again, whatever.
My question is that given this problem, years ago before I started writing in python I wrote some short programs in python which could, in fact, busy both my CPUs. In retrospect I assume I did not have code in my run function that causes a GIL lock... so I have done this again. I start two threads... I use gkrellm to watch my processors (dual processor machine). If I merely print a number... both CPUS are getting 90% simultaneous loads. If I increment a counter and print it too, the same, and if I create a small list and sort it, the same. I did not expect this... I expected to see one processor pegged at around 100%, which should sometimes switch to the other processor. Granted, the same program in C/C++ would peg both processors at 100%... but given that the overhead in the interpreter cannot explain the extra usage, I assume the code in my thread's run functions is actually executing non-serially. I assume this is because what I am doing does not require the GIL to be locked for a significant part of the time my code is running... what code could I put in my run function to see the behavior I expected? What code could I put there to take advantage of the possibility that really the GIL is not locked enough to cause actual serialization of the threads... anyone care to explain? -- http://mail.python.org/mailman/listinfo/python-list
