I am using Python 2.2.2 on RH9, and just starting to work with Python
threads.
I started using the threading module and found that 10-20% of the runs
of my test program would hang. I developed smaller and smaller test
cases, finally arriving at the program at the end of this message,
which uses the thread module, not threading. This program seems to
point to problems in Python thread scheduling.
The program is invoked like this:
python threadtest.py THREADS COUNT
THREADS is the number of threads created. Each thread contains a loop
that runs COUNT times, and all threads increment a counter. (The
counter is incremented without locking -- I expect to see a final
count of less than THREADS * COUNT.)
Running with THREADS = 2 and COUNT = 100000, most of the time, the
program runs to completion. About 20% of the time however, I see one
thread finish, but the other thread never resumes.
Here is output from a run that completes normally:
[EMAIL PROTECTED] python threadtest.py 2 100000
nThreads: 2
nCycles: 100000
thread 1: started
thread 1: i = 0, counter = 1
thread 2: started
thread 2: i = 0, counter = 2691
thread 1: i = 10000, counter = 13496
thread 2: i = 10000, counter = 22526
thread 1: i = 20000, counter = 27120
thread 2: i = 20000, counter = 40365
thread 1: i = 30000, counter = 41264
thread 1: i = 40000, counter = 55922
thread 2: i = 30000, counter = 58416
thread 2: i = 40000, counter = 72647
thread 1: i = 50000, counter = 74602
thread 1: i = 60000, counter = 88468
thread 2: i = 50000, counter = 99319
thread 1: i = 70000, counter = 110144
thread 2: i = 60000, counter = 110564
thread 2: i = 70000, counter = 125306
thread 1: i = 80000, counter = 129252
Still waiting, done = 0
thread 2: i = 80000, counter = 141375
thread 1: i = 90000, counter = 147459
thread 2: i = 90000, counter = 155268
thread 1: leaving
thread 2: leaving
Still waiting, done = 2
All threads have finished, counter = 168322
Here is output from a run that hangs. I killed the process using
ctrl-c.
[EMAIL PROTECTED] python threadtest.py 2 100000
nThreads: 2
nCycles: 100000
thread 1: started
thread 1: i = 0, counter = 1
thread 2: started
thread 2: i = 0, counter = 990
thread 1: i = 10000, counter = 11812
thread 2: i = 10000, counter = 13580
thread 1: i = 20000, counter = 19127
thread 2: i = 20000, counter = 25395
thread 1: i = 30000, counter = 31457
thread 1: i = 40000, counter = 44033
thread 2: i = 30000, counter = 48563
thread 1: i = 50000, counter = 55131
thread 1: i = 60000, counter = 65291
thread 1: i = 70000, counter = 78145
thread 2: i = 40000, counter = 82715
thread 1: i = 80000, counter = 92073
thread 2: i = 50000, counter = 101784
thread 1: i = 90000, counter = 104294
thread 2: i = 60000, counter = 112866
Still waiting, done = 0
thread 1: leaving
Still waiting, done = 1
Still waiting, done = 1
Still waiting, done = 1
Still waiting, done = 1
Still waiting, done = 1
Still waiting, done = 1
Still waiting, done = 1
Still waiting, done = 1
Traceback (most recent call last):
File "threadtest.py", line 26, in ?
time.sleep(1)
KeyboardInterrupt
[EMAIL PROTECTED] osh]$
In this case, thread 1 finishes but thread 2 never runs again. Is
this a known problem? Any ideas for workarounds? Are threads widely
used in Python?
Jack Orenstein
# threadtest.py
import sys
import thread
import time
nThreads = int(sys.argv[1])
nCycles = int(sys.argv[2])
print 'nThreads: %d' % nThreads
print 'nCycles: %d' % nCycles
counter = 0
done = 0
def run(id):
global done
print 'thread %d: started' % id
global counter
for i in range(nCycles):
counter += 1
if i % 10000 == 0:
print 'thread %d: i = %d, counter = %d' % (id, i, counter)
print 'thread %d: leaving' % id
done += 1
for i in range(nThreads):
thread.start_new_thread(run, (i + 1,))
while done < nThreads:
time.sleep(1)
print 'Still waiting, done = %d' % done
print 'All threads have finished, counter = %d' % counter
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