On 15/04/2011 20:17, Dan Stromberg wrote:
On Fri, Apr 15, 2011 at 9:33 AM, Chris H
<chris.humph...@windsorcircle.com> wrote:
1. Are you sure you want to use python because threading is not good due to
the Global Lock (GIL)? Is this really an issue for multi-threaded web
services as seems to be indicated by the articles from a Google search? If
not, how do you avoid this issue in a multi-threaded process to take
advantage of all the CPU cores available?
Concurrency in Python is a largish topic.
It's true that CPython's multithreading is poor. In fact, running a
multithreaded CPython application on n vs 2n cores can actually take
more time on the 2n cores.
However:
1) In Jython, and likely IronPython, threading is good.
The load times of Iron Python are ssslllooooowwwww!
(My tests showed startup times 4 to 6 times that of cpython on the same
kit).
3) There's something called "stackless" and (similar to stackless)
"greenlets". While stackless allows you to use thousands of threads
comfortably, it's still pretty single-core. It's essentially a fork
of CPython, and is being made a part of PyPy. I believe greenlets are
an attempt to bring what's good about stackless to CPython, in the
form of a C extension module.
Greenlets are green threads - cooperative switching all in one system
thread
and therefore one core. Very lightweight.
4) I've heard that in CPython 3.2, the GIL is less troublesome, though
I've not yet heard in what way.
Multiple threads still cannot run at the same time, however, if one
thread runs too
long without a context switch, it relinquishes control and forces
another thread to run.
This stops a low priority thread on one core, locking out a
high-priority thread on
another. That this was happening is why 2 cores can be slower than one.
(The overhead
of starting the second thread, finding it can't get the GIL and closing
down again).
5) Even in CPython, I/O-bound processes are not slowed significantly
by the GIL. It's really CPU-bound processes that are.
Its ONLY when you have two or more CPU bound threads that you may have
issues.
Regards
Ian
--
http://mail.python.org/mailman/listinfo/python-list
