Re: [Sablevm-developer] Threading support in SableVM

[Etienne G. <gag...@uq...>]

Hi All,

First, I'll be away for a little over 2 weeks, so don't expect any
reply from me.

See comments below.

Chris Pickett wrote:
> ...
> For the Pentium 4, Intel Xeon, and P6 family processors, if the area of 
> memory being locked during a LOCK operation is cached in the processor 
> that is performing the LOCK operation as write-back memory and is 
> completely contained in a cache line, the processor may not assert the
> LOCK# signal on the bus....
> ... 
> So that means it looks like the problem is elsewhere (e.g. writes to 
> "xxx.flag" that Etienne mentioned). ...

Hmmm...  I'm not convinced.  Have you actually read the JVM spec for
JMM (memory model)?  Acquiring a thin lock should cause all UNRELATED
memory content to be gotten from main memory after the lock, and
unlocking should do the reverse.  SableVM does not do any of this
currently.  It's not a problem on uniprocessors, but I expect this to
be quite a problem on MPs.  My language, here, is quite fuzzy; it would
be best explained in terms of "read/write" barriers, yet I have to find
a "reliable" definition of "barriers" which would be consistent across
MPs.

Etienne

-- 
Etienne M. Gagnon, Ph.D.             http://www.info.uqam.ca/~egagnon/
SableVM:                                       http://www.sablevm.org/
SableCC:                                       http://www.sablecc.org/