Re: Question on threads

Jonathan Shao wrote:

On Fri, Apr 11, 2008 at 3:29 PM, Steve Holden <st***@holdenweb.com
<mailto:st***@holdenweb.com>wrote:

Jonathan Shao wrote:

Hi all,
I'm a beginner to Python, so please bear with me.
Is there a way of guarenteeing that all created threads in a
program are finished before the main program exits? I know that
using join() can guarentee this, but from the test scripts I've
run, it seems like join() also forces each individual thread to
terminate first before the next thread can finish. So if I
create like 20 threads in a for loop, and I join() each created
thread, then join() will in effect cause the threads to be
executed in serial rather than in parallel.
No it won't, as in fact there is no mechanism to force a thread to
terminate in Python. When you join() each created thread the main
thread will wait for each thread to finish. Supposing the
longest-lived thread finished first then all others will immediately
return from join().

The only requirement it is imposing is that all sub-threads must be
finished before the main thread terminates.

regards
Steve
--
Steve Holden +1 571 484 6266 +1 800 494 3119
Holden Web LLC http://www.holdenweb.com/

I guess I'm doing something wrong with join(). Here's a test script I
wrote up...

import threading
import time
class TestThread(threading.Thread):
def __init__(self, region):
self.region = region
threading.Thread.__init__(self)
def run(self):
for loop in range(10):
print "Region " + str(self.region) + " reporting: " + str(loop)
time.sleep(2)
for x in range(10):
thr = TestThread(x)
thr.start()
thr.join()
raw_input()
In this script thread 0 will finish first... Am I doing something wrong
with join()?

Yes - you are calling it before you have started ALL your threads,
thereby making hte main thread wait for the end of thread 1 before
starting the next. An impressive demonstration of thread
synchronization, but not quite what you want :-)

Try saving the threads in a list then joining them later, like this
(untested):

threads = []
for x in range(10):
thr = TestThread(x)
thr.start()
threads.append(thr)
# Now all are started, wait for all to finish
for thr in threads:
thr.join()

regards
Steve
--
Steve Holden +1 571 484 6266 +1 800 494 3119
Holden Web LLC http://www.holdenweb.com/