Future of CMS

Volker Simonis volker.simonis at gmail.com
Sat Jun 11 13:37:48 UTC 2016

Hi Jon,

I'm a little bit disappointed that you didn't think about SAP when you sent
your initial mail ;)

But seriously: SAP is supporting CMS and will probably do so for quite a
long time (simply because we do support old Java releases for a very long

Completely removing CMS from the HotSpot code base may increase these
support costs considerably for us.

Do you plan to really delete the sources from the repos or do you only plan
to disable it at build time?

I think only disable it at build time would make it easier for us and
others to still support it in the future. But in that case we really have
to come up with a better development model which would allow external
developers to directly push CMS changes (much like ppc64 or aarch64
changes). Everything else would be a real PITA.

Thank you and best regards,

On Saturday, June 11, 2016, Jon Masamitsu <jon.masamitsu at oracle.com> wrote:

> Added hotspot-gc-dev.
> On 6/10/2016 6:17 PM, Jon Masamitsu wrote:
>> Jungwoo, Ramki, Tony (and other friends of CMS),
>> I wanted to be sure you guys saw this JEP.
>> Deprecate the CMS garbage collector (UseConcMarkSweepGC).
>> http://openjdk.java.net/jeps/8142518
>> I know you do development on CMS and wanted to know if
>> had thoughts about the future of CMS.
>> At some point Oracle is going to stop supporting CMS.
>> The burden of testing and maintaining the CMS code doesn't
>> make much sense given that we think G1 is the better
>> collector.    If we deprecate CMS in jdk9, support would be dropped
>> no earlier than jdk10.
>> Have you guys talked about what you would like to do with regard
>> to continuing CMS development without Oracle's help?
>> I've been told that if CMS exists in the Oracle binaries, then
>> customers will expect it to work.  So not supporting CMS
>> means it is not in the build.
>> Jon
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