Python Threading With Concurrency

Question

I wrote the following code while trying to learn threading in python.

    import threading
    import time

    def printWorker(x,y):
        t = time.time()
        while time.time() - t < 10:
            print "Name:%s  Time:%s" %(y,str(time.time() - t))
            time.sleep(x)

    t1 = threading.Thread(target = printWorker(2,'Thread-1'))
    t2 = threading.Thread(target = printWorker(3,'Thread-2'))

    t1.start()
    t2.start()

Im trying to get an output where both Thread-1 and Thread-2 start at same time. IE Print

Thread-1 Stuff, Thread-2 Stuff, Thread-1 Stuff, Thread-2 Stuff, instead of

Thread-1 Stuff, Thread-1 Stuff, Thread-1 Stuff, Thread-1 Stuff, Thread-2 Stuff, Thread-2 Stuff, Thread-2 Stuff, Thread-2 Stuff

Instead Thread-2 Only starts after Thread-1. I've checked online examples but I don't understand what I'm doing wrong mechanically.

FogleBird · Accepted Answer · 2011-11-27 18:03:14Z

4

To pass arguments you need to do this:

t1 = threading.Thread(target=printWorker, args=(2, 'Thread-1'))
t2 = threading.Thread(target=printWorker, args=(3, 'Thread-2'))

Your code is invoking printWorker on the main thread and starting two threads with target=None (the return value of printWorker).

answered Nov 27, 2011 at 18:03

FogleBird

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4 Comments

kal Over a year ago

Wow thanks a lot for that help. Also could you point me in a direction where i can understand args and kwargs. Thank you very much. :)

Vilas Over a year ago

Even after fixing this you might not necessarily observe "Thread-1 Stuff, Thread-2 Stuff, Thread-1 Stuff, Thread-2 Stuff" since you are not doing anything to guarantee the enforcement of that particular schedule. Sleeps are not a reliable mechanism for enforcing required thread scheduling.

kal Over a year ago

I know sleeps arent reliable. This was just a test to see if they are running asynchronously or synchronously.

Vilas Over a year ago

Ok. Another recommended practice: parent threads should call join on the threads they have started :)

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