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From Justin Erenkrantz <jerenkra...@ebuilt.com>
Subject Re: DCEthreads - cancellation / mutexes is possible
Date Tue, 17 Jul 2001 15:47:09 GMT
On Tue, Jul 17, 2001 at 03:26:29PM +0200, Luke Kenneth Casson Leighton wrote:
> therefore, i conclude that the dce/rpc codebase has successfully
> implemented thread cancellation in their POSIX/Draft4 thread
> library.
> 
> additionally, the context app, being threaded, has to have
> locking on the little 'stores' it maintains.  i do not know
> what it means [well, okay, i do, but i've never actually
> programmed with threads is more like it] but there is some
> code in there that mentions 'mutex'.
> 
> i presume that this is working, too.
> 
> does this help answer your question, justin?

I don't like cancellation of threads from a design perspective.  I don't
care much that some test "works."  It wasn't an issue of whether the
underlying OS supports cancellation of threads - it was an issue that
this now becomes a nightmare to code up correctly.  We now need to add
cancellation points, and there are certain activities that the thread
may enter which are non-cancellable no matter what we do (i.e. mutex
acquisition).  AIUI, the dce/rpc codebase is a commercial *user-space* 
threading add-on.  Yuck.  -1 on dce/rpc for that aspect alone.  

-1 on having cancellation of threads based on the overall design.  I 
abhor the idea of a thread being forced to exit against its wishes.  
It will just lead us down a road that I don't wish to go down in APR.
Now, if someone wants to write a httpd MPM that uses cancellation,
be my guest.  I can't stop you (I don't have commit access there and 
hence veto power).  In fact, before even considering cancellation 
support in APR, I'd want to see a MPM that uses cancellation properly
and is just as robust (hehe) as the current threading MPM.  When that
occurs, I might be willing to reconsider.

And, from what I can tell, Dean Gaudet has mentioned this morning that 
he is willing to veto async notification.  Dean, would that include 
cancellation of threads?  I have a suspicion it might.  Dean has 
commit access on httpd as well, so if you can convince Dean to 
change his mind, I'll change mine.  -- justin


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