Question

I’m hoping that someone has a quick and easy solution to this issue that I’m facing. I’m working through chapter 5 of the 4th edition of the Programming Python book by Mark Lutz and I’m having some troubles beginning on page 189. Basically, there is a very simple example:

import _thread
def action(i):
    print(i ** 32)

_thread.start_new_thread(action, (2, ))

For some reason, this script will not produce any output on my pc running Ubuntu 12.04, but will on my windows 7 machine. The output when run from the terminal is:

un@homepc:~/Desktop/pp$ python3.2 thread1.py
un@homepc:~/Desktop/pp$ 

Any help would be much appreciated.

Thanks.

Answer 1

I am not an expert of threads but this is most likely the problem:

When running this code, Python has nothing to do after the last line;so it exits forcefully ending the thread (whether it completed or not).
Depending on how the threads run, the thread may complete or it may not. (unreliable behaviour)

main thread pseudo-code instruction:

create the new thread

new thread:

action(2)

main thread next instruction:

program ended;exit

Fixed code:

import _thread
def action(i):
    print(i ** 32)
    action_lock.release() #Now Python will exit

#locks are a part of threaded programming; if you don't know what it is, you can google it.
action_lock = _thread.allocate_lock() #set a lock for the action function thread
action_lock.acquire() #Acquire the lock
_thread.start_new_thread(action, (2, ))
action_lock.acquire()