[python-win32] Geting values from a thread

[Tim Roberts]

On Mon, 10 Jan 2005 19:41:55 +0100, python at kareta.de wrote:

>Hi all,
>
>I am wondering about the following situation:
>
>I defined a class and inside this class I start a new thread with
>thread.start_new_thread. When I set some attributes of that class inside
>the thread_function, the attributes are not changed.
>
><code>
>class test:
>   def __init__(self):
>       self.param=''
>       thread.start_new_thread(self.run_thread,())
>   def run_thread(self):
>       self.param='hello'
>       return
>
>t=test()
>print t.param #result is an empty string
></code>
>The run_thread function operates on the same object but all changes are lost
>when the thread returns. How can I pass values from the thread function to the
>main thread ?
>  
>

You are misdiagnosing the problem.  The problem is that the __init__ 
function returns and your print statement executes before the run_thread 
function has had a chance to run.  Your main thread then exits, 
self.param gets set, and the second thread exits.

That's the whole advantage of threads: they run independently.

If you really need to communicate like this, you'll need to use a Queue 
or some other kind of interlock.  However, if you DO find yourself 
waiting like this very often, then it is quite likely that threads are 
not the right answer for your problem.

-- 
- Tim Roberts, timr at probo.com
  Providenza & Boekelheide, Inc.