[concurrency-interest] question the about the JMM

Larry Riedel larryr at saturn.sdsu.edu
Wed Dec 5 16:37:38 EST 2007


> reasoning in 'caches and invalidation' is not the way to
> go with the new JMM.

I think it should be ok to reason that way, as long as it is
done in a way which is consistent with the actual semantics,
which I think is viable.  It seems to me kind of like saying
a lock is "protecting a critical section of code" rather
than "protecting some objects".  If I say thinking the
latter is the way to go, maybe it would not be unreasonable
for someone to say to me "but it is the critical sections of
code that access the objects".

If somebody was to think like "whenever I release a lock,
the caches get invalidated, and by the time another thread
has acquired a lock after that, the caches will have been
updated", where "after" is defined in terms of real world
time, it seems to me like something close to that could
be part of a valid model for somebody who wants to think
in terms of one single real world time, as long as they
are careful about which caches and locks, and which object
values are in the caches.

If someone thinks whenever a thread acquires/releases
a lock, it will see the latest changes any other thread
made to any value prior to the most recent acquire/release
of a lock in that thread, it seems like they may just be
misinformed, rather than using a fundamentally poor model.


Larry



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