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How to check for threads being finished in python?

0 votes
62 views

I have a pool of worker threads, created like this:

threads = [MyThread(*args) for i in range(numthreads)]
for t in threads:
 t.start()

I then block until the threads are all done:

while any(t.isAlive() for t in threads):
 pass

Is that the right way to wait for the threads to be done? Should I stick a call to time.sleep() inside the while loop? If so, how long should I sleep? That's probably an unanswerable question, but some guidelines on
choosing the sleep time will be appreciated.

posted Jul 5, 2013 by anonymous

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3 Answers

+1 vote

Using the threading module, I assume. Is there any reason you can't simply join() each thread in succession?

answer Jul 5, 2013 by anonymous
+1 vote

I think your while loop busy-waits until the threads are completed. Do this instead:

for t in threads: t.join() # optionally pass a timeout to join
answer Jul 5, 2013 by anonymous
+1 vote

If you are just going to wait for them to finish, and never use them again...

for t in threads:
 t.join()

Doesn't matter which thread ends first, this operation will either block if the thread hasn't finished or cycle to the next thread if it has.

answer Jul 5, 2013 by anonymous
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0 votes

This is my first script where I want to use the python threading module. I have a large dataset which is a list of dict this can be as much as 200 dictionaries in the list. The final goal is a histogram for each dict 16 histograms on a page ( 4x4 ) - this already works.
What I currently do is a create a nested list [ [ {} ], [ {} ] ] each inner list contains 16 dictionaries, thus each inner list is a single page of 16 histograms. Iterating over the outer-list and creating the graphs takes to long. So I would like multiple inner-list to be processes simultaneously and creating the graphs in "parallel".
I am trying to use the python threading for this. I create 4 threads loop over the outer-list and send a inner-list to the thread. This seems to work if my nested lists only contains 2 elements - thus less elements than threads. Currently the scripts runs and then seems to get hung up. I monitor the resource on my mac and python starts off good using 80% and when the 4-thread is created the CPU usages drops to 0%.

My thread creating is based on the following : http://www.tutorialspoint.com/python/python_multithreading.htm


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