Re: System wide JVMs

[Blair Wyman <blairw@xxxxxxxxxx>]

Not sure where you heard that "the iSeries JVM actually pauses execution in
the JVM to do clean up," but it's simply not the case.  In fact, the
asynchronous nature of the iSeries' GC algorithms helped push us to our
early domination of the specJBB benchmark.

The only exception to this generally asynchronous behavior -- where mutator
threads are actually paused -- occurs when an attempt to allocate storage
would cause the JVM to exceed its maximum heap size.  (Before throwing an
OutOfMemoryError the JVM is required to "try real hard" to collect
everything it can.)

FWIW, the design of the iSeries JVM GC was originally based on "Portable,
Unobtrusive Garbage Collection for Multiprocessor Systems", Doligez and
Gonthier, POPL 1/94, but has seen several improvements over the years from
colleagues in IBM Research division (notably Haifa).

Just wanted to set the record straight.

-blair


  ___   _           Blair Wyman                  IBM Rochester
 ( /_)  /  _  ' _   (507)253-2891            blairw@xxxxxxxxxx
__/__)_/_<_/_/_/_'  Opinions expressed may not be those of IBM



                                                                           
             "Jim McLean"                                                  
             <Jim.McLean@farro                                             
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                                       System wide JVMs                    
             07/06/2004 12:58                                              
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Guys,

I think the main reason why there aren't system wide JVMs is for code
security/stability.  Wouldn't it be kinda crazy if all Java processes were
using the same JVM?  Processes could just start screwing with other
processes session type objects whenever they felt like it.  What about
garbage collection in this huge JVM?  As far as I know the iSeries is a bit
different in terms of GC compared to the typical background process.  The
iSeries JVM actually pauses execution in the JVM to do clean up.  I think
we would have alot of clean-up to do if we have processes entering and
leaves the same JVM all the time.

Just throwing out what I see as some potential problems...