RFR(S): 8068579: Running with -XX:-UseParallelGC does not turn ParalleGC off

[Jon Masamitsu]

On 3/15/2016 6:48 AM, Per Liden wrote:
> Summary: Explicitly disabling the default collector, without 
> specifying another collector, will silently re-enable the default 
> collector. This is a bit counter intuitive. A better approach would be 
> for the VM to complain about the situation.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8068579
> Webrev: http://cr.openjdk.java.net/~pliden/8068579/webrev.0/

Changes look good.

Not part of your changes bug should this code mostly be under
INCLUDE_ALL_GCS?

Jon

> Testing: manual, jprt
>
> Example (assuming it's a platform/configuration with G1 as default):
>
> $ java -XX:-UseG1GC ...
>
> Today, the above command will happily start a VM with G1 enabled.
>
> With this patch the VM will instead complain, like this:
>
> $ java -XX:-UseG1GC ...
> Error occurred during initialization of VM
> Garbage collector not selected (default collector explicitly disabled)
>
> And of course, we're good with disabling the default collector as long 
> as you specify some other collector, e.g.:
>
> $ java -XX:-UseG1GC -XX:+UseParallelGC ...
>
> cheers,
> Per