Re: [Webmacro-devel] Bad interaction with TimeLoop and cache time s?

[<web...@st...>]

On Thu, 16 Jan 2003, Brian Goetz wrote:

| > because the cache is immutable and therefore can be used unsynchronized.
|
| ... on uni-processor systems, or on multi-processor systems that have
| a stronger memory model than the JLS requires, which would include Intel,
| but not PPC, Alpha, or some configurations of Sparc ...

This I have also always though about: you _cannot_ go about being
unsynchronized "all the time" on such non-cache-synched systems, thus
probably raising problems for Lane's cache.

HOWEVER, isn't entering a synchronized block actually committing
_everything_ of that thread's unflushed cache back to memory (and
invalidating it)? So that, if this is in a servlet, then you _would_ have
had some synchronized blocks around some other part of the system/engine.
Wouldn't this also have changed the reference to the "unsynched" map of
Lane? - The system works by having one unsynched map, and one synched "for
backup".  Then, after some time, the synched map is remade to be a
unsynched map, and then put in place of the existing unsynched map. The
problem is of course that this won't propagate to the 'other processors'
on the system..

Well..

If the synch-semantics require _all_ cache to be flushed back to main
memory, wouldn't this _eventually_ propagate to the other processors, in a
consistent way, with e.g. the next HttpSession lookup by the servlet
container?

If not, what if the reference to the synched map is declared 'volatile'?
Would that change anything? What happens to the objects in the map? Would
you actuall be able to get hold of memory areas that weren't initialized,
as the other thread would have freed some parts of his view of the memory
(e.g. freeing the synched map), and then allocated some (and overlapping)
parts of the memory to the new map (which he puts to the volatile
reference).. ?

If those questions just sounds stupid, I must have phrased myself wrongly,
because they aren't stupid! No-one has answered them satisfactory yet! ;)
I would love if for example you, Brian, gave it a shot!


-- 
Mvh,
Endre Stølsvik               M[+47 93054050] F[+47 51625182]
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