Understanding threading

Question

Trying to get my head around threading. In my code, it's only firing one thread, when I think it should go straight on to the second. I've been reading about locks and allocating but don't quite understand. What would I need to do here to let 2 threads run independently at the same time?

import thread

def myproc(item):
    print("Thread fired for " + item)
    while True:
        pass

things = ['thingone', 'thingtwo']

for thing in things:
    try:
        thread.start_new_thread(myproc(thing))

    except:
        print("Error")

Answer 1

You've got the signature to start_new_thread wrong. You're calling myproc and passing the result as an argument to start_new_thread, which never happens as myproc never terminates.

Instead, it should be:

thread.start_new_thread(myproc, (thing,) )

The first argument is the function (ie. the function object, not calling the function) and the second is a tuple of arguments.

See: https://docs.python.org/2/library/thread.html#thread.start_new_thread

Once you have your program actually starting both threads, you probably want to add a pause at the end because the threads will terminate when the main thread finishes.

Also, please consider using the threading module instead of the thread module, as it provides a much nicer higher level interface, such as a convenient way for waiting until your threads have finished executing.

See: https://docs.python.org/2/library/threading.html#module-threading