Re: deferred cancellation of ipc

[Marcus Brinkmann]

On Tue, Oct 14, 2003 at 04:00:35PM -0700, Volkmar Uhlig wrote:
> After reading your initial scenario again there is a rather simple
> solution--use zero timeouts.  Instead of storing the cancel flag you
> store the intended send timeout value, which could be zero.  Of course
> you still run into a race on MP if you don't use some synchronization
> primitive, but that is a different issue you have to deal with anyway.  
> This solution assumes that you _only_ want to ensure that the thread
> does not block.

That doesn't seem to give me any relief.  If I see the zero timeout in my
thread for the IPC, I can also see a cancel flag and exit right away.  I can
do a quick poll on the IPC, if I want to, but as you said, the
synchronization problem has to be solved, because the race happens if the
cancel happens after I checked the cancel flag and before I enter the IPC
call.
 
> > Or does maybe stopping a thread on another CPU count as 
> > preemption and is also delayed?
> 
> Sorry, but I don't get what you mean.  What is "stopping"; exregs?

Yes.  Also called halting.  If I stop/halt a thread on another cpu, will
this stop/halt the thread even if it delayed preemption?  Or does preemption
delay prevent that?

Thanks,
Marcus

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Marcus Brinkmann              The Hurd http://www.gnu.org/software/hurd/
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