[Info-vax] Still no DIR/SORT_BY_TIME

[Simon Clubley]

On 2015-08-18, Stephen Hoffman <seaohveh at hoffmanlabs.invalid> wrote:
> On 2015-08-18 18:01:09 +0000, David Froble said:
>> It's always possible to not conform to locking.  Just be careful when 
>> doing so.  Read only usually is safe.
>
> Constants?  Entirely read-only, with no changes to the values?  Sure.   
> But beware of shared memory on Alpha multiprocessors: 
> http://labs.hoffmanlabs.com/node/407
>

Another variant of that (on some ARM MCUs) is when your peripherals are
on an internal bus and register updating isn't instantaneous because the
device register updates are posted across the bus.

In that case, you need to use a Data Synchronisation Barrier in your
interrupt handler wrapper or a race condition occurs in which it's
possible to take a second interrupt for the same event when you return
from your interrupt routine.

It's not only multiprocessor shared memory which needs barriers... :-)

Simon.

-- 
Simon Clubley, clubley at remove_me.eisner.decus.org-Earth.UFP
Microsoft: Bringing you 1980s technology to a 21st century world