JEP 291: Deprecate the Concurrent Mark Sweep (CMS) Garbage Collector

kirk at kirk at
Fri Jul 1 17:24:36 UTC 2016

Hi Jon,

I’ve reversed engineered startup parameters and the result is a chart of all possible flag settings and their outcomes. I’d be happy to share it with you as I believe it shows a way to prevent CMS from being turned on. That said, I would consider this approach to be a hack and I’m not sure it should be used. However it does suggest there is a way to prevent CMS from being activated. BTW, it can’t be turned on after the JVM is initialized.

Kind regards,
Kirk Pepperdine

> On Jul 1, 2016, at 5:12 PM, Jon Masamitsu <jon.masamitsu at> wrote:
> On 7/1/2016 7:39 AM, Andrew Haley wrote:
>> On 01/07/16 15:36, Jon Masamitsu wrote:
>>> Do you have a suggestion on how continued support for CMS in OpenJDK
>>> would work?  I've been told that if CMS is built in the binaries that Oracle
>>> distributes, then customers will expect Oracle to support it. Regardless
>>> of what the release notes say.
>> How are they to know that it's in there?
> If nothing else, it's open source.  :-)
>>  All you have to do is
>> disable the option in Oracle builds.
> It seems like that should be enough, but I honestly don't know.
> If there's some squirrely way for a customer to turn it on
> (jcmd, start up script, who knows what), we'd be stuck.
> I think Oracle is very care about such things.  If asked, "Is there
> any possible way that CMS could be turned on?",  the best
> I could do would be to say, "I don't think so".  Not good enough.
> Jon
>> Andrew.

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