JDK-8027132: Print deprecation warning message for the flags controlling the CMS foreground collector

[Erik Helin]

Bengt,

looks even better :)

Thanks,
Erik

On 2013-10-24, Bengt Rutisson wrote:
> 
> Thanks for the reviews Erik and Stefan!
> 
> Thomas suggested to add a JTreg test for these flags. Here is a
> webrev with the same code change as before but with a test added:
> 
> http://cr.openjdk.java.net/~brutisso/8027132/webrev.01/
> 
> Thanks, Thomas for pointing this out.
> 
> Bengt
> 
> 
> On 2013-10-24 14:26, Erik Helin wrote:
> >Hi Bengt,
> >
> >looks good, thanks for doing this!
> >
> >Erik
> >
> >On 2013-10-24, Bengt Rutisson wrote:
> >>Hi all,
> >>
> >>Can I have a couple of reviews for this small change?
> >>
> >>http://cr.openjdk.java.net/~brutisso/8027132/webrev.00/
> >>
> >>CR: https://bugs.openjdk.java.net/browse/JDK-8027132
> >>
> >>Background from the CR:
> >>
> >>Normally CMS reverts to the SerialOld GC when it needs to do a full
> >>GC. There is a mode in CMS to instead use the "foreground
> >>collector".  This is a single threaded stop-the-world mode which
> >>completes an ongoing concurrent CMS collection (a normal
> >>"background" collection in CMS).
> >>
> >>The foreground collector is very slow and to enable it two flags are
> >>required. First -XX:-UseCMSCompactAtFullCollection needs to be added
> >>to the command line to turn off the SerialOld collector, then
> >>-XX:CMSFullGCsBeforeCompaction needs to be set to a value greater
> >>than 0.
> >>
> >>The foreground collector adds a lot of complexity to the CMS code
> >>but has few (if any?) use cases. Thus, it would be good to remove it
> >>to simplify the code. In order to remove it we need to deprecate it
> >>first. This bug report is only about deprecating the flags to allow
> >>us to remove the foreground collector in a future release.
> >>
> >>The following flags should log a warning message that they are
> >>deprecated, but the VM should still continue to work when they are
> >>used:
> >>
> >>UseCMSCompactAtFullCollection
> >>CMSFullGCsBeforeCompaction
> >>UseCMSCollectionPassing
> >>
> >>Thanks,
> >>Bengt
>