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From "Weldon Washburn" <weldon...@gmail.com>
Subject [drlvm/mmtk] jitrino.jet write barrier design questions
Date Wed, 21 Jun 2006 23:06:01 GMT
It would be really nice if jitrino.jet allowed the write barrier to be
selected at the start of jitting an individual method.   Is this

The selections would be mutually exclusive:
no write barrier (for the existing GCV4)
write barrier written in Java (for MMTk)
write barrier written in C  (for the yet to be determined basic generational GC)

Allowing the "java" write barrier to be selected on a method by method
basis would be very useful for MMTk bring up.  The concept is to
initially run MMTK sort of like a "user mode linux".  That is, startup
the JVM w/o barriers turned on.  Run "hello world".  Then switch on
MMTK collector/allocator and Java write barriers and compile/run the
following method:

public class InitialMMTkBringup {

    public int stressTheMMTkAllocator ()  {
       while(true) {
         Object obj = new Object();
         Object [] ia = new Object[100];
         //at a later stage, add code that causes a write barrier
         //at a later stage, add code that will randomly chain Object
arrays together...

The above would be running while the underlying JVM GC is running.  If
not careful this could cause lots of confusion.  The intention is to
run MMTk in "user mode" only to the point where MMTk alloc,
collection, write barrier code paths are exercised.  Provided we do
not do anything to cause the underlying JVM GC to kick in, we should
be OK.

As a second step actually integrate MMTk into the JVM.  Note that
basic garden variety Java debugger should work w/o modification with a
"user mode MMTk".

Weldon Washburn
Intel Middleware Products Division

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