17 Dec
2024
17 Dec
'24
4:19 a.m.
On Dec 16, 2024, at 7:40 AM, Douglas McIlroy <douglas.mcilroy(a)dartmouth.edu> wrote:
May be this has to do with using POSIX on multiprocessor systems that
are *not* cache coherent? May be less of an issue for now[1] though but
weren't there such systems in the past?
In any case shared access by itself is not enough for proper operation.
Bakul
[1] Given very high clock rates and increasing # of cores, I wonder
how long before they start using CSMA/CD for coherency protocols!
... When multiple processes map the same memory
object, they can
share access to the underlying data.
Notice the weasel word "can". It is not guaranteed that they will do so
automatically without delay. Apparently each process may have a physically
distinct copy of the data, not shared access to a single location.