[TUHS] mmap, was SCCS, TeamWare, BitKeeper, and Git

[Bakul Shah via TUHS]

On Dec 16, 2024, at 7:40 AM, Douglas McIlroy <douglas.mcilroy at dartmouth.edu> wrote:
> 
> 
>> ... 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.

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!