harmony-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Weldon Washburn" <weldon...@gmail.com>
Subject [DRLVM][GC] Goals for 2006/2007
Date Mon, 14 Aug 2006 17:23:05 GMT

There is rough consensus that the immediate goal for Harmony JVM is to
reliably run simple commercial workloads with acceptable performance.
In regards to a garbage collector for a Harmony JVM in 2006 there are
some data points worth noting.  1) A quick survey shows most basic
commercial JVMs implement a generational collector. 2) While the
existing drlvm garbage collector, gcv4, implements some interesting
advanced concepts, it is not currently a generational collector.  3)
The MMTk port to drlvm is not yet finished.  Even assuming MMTk's
generational configuration is appropriate, it is still too early to
put this garbage collector on the roadmap for a 2006 Harmony JVM.  It
might be worth revisiting in 2007.  But it's too far away to debate at
this time.

Given the above data points, the following is a first stab at
requirements for Harmony "GCV5".  The intention is to set down some
basic parameters.

Generational Collector with mark/compacting mature object space

Parallel collection, no concurrent collection (Editor's note: parallel
collection is a specific term meaning that during gc collection, most
CPUs in an SMP box are busy collecting garbage.  This is fairly
straight forward to build.  Concurrent collection is a specific term
meaning that Java application threads make forward progress while
special GC threads are simultaneously collecting.  This is hard to

Parallel allocation. (Again, this is very straight forward.  Basically
each Java thread gets private chunks of memory to allocate out of.)

Write barriers.  A generational collector benefits from write barriers
that detect whenever a pointer to a younger object is written inside
an older object.

For expediency, GCV5 should try to plug into the existing JVM/GC
interface.  However, if this interface is broken, we need to jump at
the opportunity to make it right.

The goal is to make this code readable/modifiable/debuggable by non-GC
engineers.  The code should read as nothing more than a basic
generational GC.  No experimental code should ever be checked into
Harmony GCV5 source base.

Performance goals should be discussed after the initial implementation
is committed.

Object pinning is not required at this time.  However, be prepared
that at a later date we might discover pinning is needed to get
acceptable performance from native methods that use JNI.

Supports Java 1.5.  This means GCV5 must implement functionality such
as weak/soft/phantom references and finalization.

Though this work will be an investment, it is ultimately necessary for
Harmony to meet medium term goals, eg., being maintainable, passing
TcK successfully, etc.  and be a platform for future, more advanced
work, which is a requirement that v4 cannot meet.

Thoughts on the above?

Weldon Washburn
Intel Middleware Products Division

Terms of use : http://incubator.apache.org/harmony/mailing.html
To unsubscribe, e-mail: harmony-dev-unsubscribe@incubator.apache.org
For additional commands, e-mail: harmony-dev-help@incubator.apache.org

View raw message