RE: FW: Java Vs RPG on iSeries

["Blair Wyman" <blairw@xxxxxxxxxx>]

On Friday, 09/20/2002 at 02:00 AST, "Steve Richter"
<srichter@autocoder.com> wrote:
[snip]

> Do all objects have a reference counter? and is the object locked when
the
> reference counter is increased/decreased?

GC does not typically use reference counting, which has trouble with cycles
of dependencies.

Traditional GC is sometimes called "mark and sweep" -- the GC thread scans
every thread (and global areas) for "root" references, and then chases
reference chains marking everything that is reachable.  When you're done,
everything that is not marked is garbage, and is swept away.

Modern collectors get a lot fancier.  Sun uses a "generational" collector
(it assumes an object that has survived a collection is likely to live a
lot longer).

iSeries uses a different scheme, originally based on "Portable, Unobtrusive
Garbage Collection for Multiprocessor Systems", Doligez and Gonthier, POPL
1/94.  Very high concurrency, in that threads are not required to pause for
long periods as some other thread scans them -- the threads scan themselves
(while servicing an interrupt), send the results to the GC thread, and then
continue on their merry way.  Very clever stuff, indeed, and accounts for
the lack of "hiccups" in the iSeries JVM, even under heavy load.

-blair

Blair Wyman -- iSeries JVM -- (507) 253-2891
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"It is a sobering thought that when Mozart was my age,
he had been dead for two years." -- Tom Lehrer