Rhialto <rhialto@falu.nl> writes:

> On Fri 18 May 2007 at 11:42:28 -0700, Bill Stouder-Studenmund wrote:
>> On Fri, May 18, 2007 at 02:52:31PM +1000, Daniel Carosone wrote:
>> >  If the upcall in question tells libpthread that the lwp has been
>> >  blocked, the upcall stack doesn't get recycled to process more
>> >  upcalls until the lwp later unblocks.
>> 
>> I don't think that's fully correct.
>> 
>> There are two different stacks involved. There's the stack of the thread 
>> that was running, made a system call, and got blocked, and then there's 
>> the stack for the upcall telling libpthread about the blockage.
>
> Why do these need to be different stacks? I would think that a blocked
> stack would make a perfect candidate for temporary use for upcalls.
>
> I'm probably missing something here, because it seems too obvious :-)

The SA/pthread library uses the stack as the thread ID, essentially,
so things like locking wouldn't work properly, because the lock owner
would be wrong.

I kept meaning to make a non-stack-ID mechanism for those
architectures that had a spare or defined stack-ID register, but it
never happened.

      - Nathan