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

[Bengt Rutisson]

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