How to kill threading.Thread instance?

Antoon Pardon apardon at forel.vub.ac.be
Mon Sep 22 14:06:50 CEST 2008


On 2008-09-21, Fredrik Lundh <fredrik at pythonware.com> wrote:
> Diez B. Roggisch wrote:
>
>>> I wonder why something like myThread.exit() or myThread.quit() or
>>> threading.kill(myThread) can't be implemented?
>>> Is something like that present in Python 3000?
>> 
>> Not that I'm aware of it (which doesn't mean to much though).
>> 
>> However I *am* aware of the bazillions discussions that have been held 
>> over this here - and the short answer is: it is a generally very bad 
>> idea to terminate threads hard, as it can cause all kinds of corruption.
>
> the problem is that you have no idea what the thread is doing, so just 
> killing it dead it may make one big mess out of the application's 
> internal state; see e.g. this post
>
>    http://mail.python.org/pipermail/python-list/2006-August/400256.html
>
>    That's wise ;-)  Stopping a thread asynchronously is in /general/ a
>    dangerous thing to do, and for obvious reasons.  For example, perhaps
>    the victim thread is running in a library routine at the time the
>    asynch exception is raised, and getting forcibly ejected from the
>    normal control flow leaves a library-internal mutex locked forever.
>    Or perhaps a catch-all "finally:" clause in the library manages to
>    release the mutex, but leaves the internals in an inconsistent state.
>
> which links to a FAQ from Sun on this very topic:
>
> http://java.sun.com/j2se/1.3/docs/guide/misc/threadPrimitiveDeprecation.html
>
> (note that Java releases all mutexes when a thread is killed, but that's 
> not much better, as the FAQ explains)
>
> so as usual, the right thing to do is to do things in the right way.

Why not let the programmer make the call whether killing the thread dead
is the right thing or not. Maybe the programmer has a pretty good idea
about what the thread can possibilbly be doing and knows that killing it
won't produce a mess.

Sure caution people to be very carefull when they are thinking about
doing something like this. Just as people are generally adviced to
use Queues when doing multithreading. But that is no reason to
disallow certain kind of actions.

-- 
Antoon Pardon



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