On Sep 17, 2:18 am, Hendrik van Rooyen <hend...@microcorp.co.za> wrote: > On Thursday 17 September 2009 06:33:05 Steven D'Aprano wrote: > > > I have two threads, one running min() and the other running max() over > > the same list. I'm getting some mysterious results which I'm having > > trouble debugging. Are min() and max() thread-safe, or am I doing > > something fundamentally silly by having them walk over the same list > > simultaneously? > > > My code is as follows. Is there anything obviously wrong with it? > > Apart from the plethora of indirection, nothing I can see. > > But there is something rotten. Going more basic, look at this: > > h...@linuxbox:~/Junk> cat jjj.py > import thread as th > import time > > a = range(10000000) > > def worker(func,thing): > start_time = time.time() > print "start time is:",start_time > res = func(thing) > print res > end_time = time.time() > print "End at:",end_time,"That took:",end_time-start_time, 'seconds' > > t1 = th.start_new_thread(worker,(min,a)) > t2 = th.start_new_thread(worker,(max,a)) > > while True: > time.sleep(1) > > h...@linuxbox:~/Junk> python -i jjj.py > start time is: 1253176132.64 > 0 > End at: 1253176133.34 That took: 0.700681209564 seconds > start time is: 1253176133.34 > 9999999 > End at: 1253176134.18 That took: 0.847566127777 seconds > Traceback (most recent call last): > File "jjj.py", line 18, in <module> > time.sleep(1) > KeyboardInterrupt > > No simultaneity.
When running min or max on a list of ints, there is probably no occasion for the function to release the GIL. If a thread doesn't release the GIL no other Python threads can run. This behavior may be rotten, but it's totally expected. Try adding "key=lambda x:x" to the function call (which adds an occasion where the GIL might be released); you will see that it will switch threads. Carl Banks -- http://mail.python.org/mailman/listinfo/python-list
