Question about Python threads
abies at pg.gda.pl
Wed Aug 28 13:19:10 CEST 2002
Armin Steinhoff wrote:
>>JVM has quite well defined semantics in presence of multiple threads
>>(including multiple processors). There are some small problems with
>>multiprocessor cache and synchronization - java memory model is in
>>process of being relaxed to allow optimized implementation.
> So the 'well defined semantic' isn't yet very well defined ... the
> processing model of JVM is at the end also not designed for
> multi-processor systems.
To be more precise.
It was well defined. It clearly stated what values field can have for
different processors given arbitrary number of threads and
synchronizations. For example, it was defined that int64 (long) access
to not have to be atomic - if you want to enforce atomiticy (sp?) you
need to wrap it in synchronization. For me, explictly saying that JVM
can update two halfs of long in non-atomic manner is a 'definition'.
Problems was with synchronization being defined too strict. To implement
it, full cache flush would be required on each synchronization. No JVM
implemented it - so we can say that all JVMs were not up to spec. Now,
this specification is being relaxed - to reflect what was really
implemented in JVMs to get reasonable performance. But again, it will be
defined - even if it will say that value can be 0 or 1, random.
But all this stuff is really not so important. What is important, is
that you can use java with multiple threads and also interact with
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