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

[Stefan Karlsson]

On 10/24/13 1:41 PM, 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

Looks good to me.

StefanK

>
> Thanks,
> Bengt