[Python-Dev] threading issue: preventing starting twice
Russell E. Owen
rowen at cesmail.net
Wed Feb 25 14:29:40 EST 2004
In the threading module, one must of course only start a thread once. I
have some questions about handling this gracefully.
First of all, the documentation only says it is an error to start a
thread more than once. It does not say which exception is raised. On my
system I find it is AssertionError. So...is that going to be true on all
systems? Is the test based on "assert", in which case it will go away
for optimized code (and then what happens)?
Anyway, if it is always AssertionError, I'd like to get the docs updated
to say that.
Also...if possible, it'd be nice to have some way to ask if a thread has
ever been started. More generally, it'd be nice to be able to determine
what state a thread is in. I'm not sure if there are any states other
than ready to run, running and finished. If that's it, perhaps one could
add methods isReady and didRun (a getState method would probably be
better if there are more states, but then one has to deal with magic
I realize it is a common Python paradigm to assume something will work
(such as starting the thread) and catch the exception if it doesn't, but:
- this is tricky if the exception is not documented
- sometimes one simply wants to know, without actually starting the
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