Unless explicitly disabled, the parallel new collector is enabled
automatically as soon as the CMS collector is enabled:
void Arguments::set_cms_and_parnew_gc_flags() {
assert(
!UseSerialGC && !UseParallelOldGC && !UseParallelGC,
"Error");
assert(UseConcMarkSweepGC, "CMS is expected to be on here");
// If we are using CMS, we prefer to UseParNewGC,
// unless explicitly forbidden.
if (FLAG_IS_DEFAULT(UseParNewGC)) {
FLAG_SET_ERGO(bool, UseParNewGC, true);
}
While it's fine to be explicit, the UseParNewGC flag is deprecatd in JDK
8 and produces warning messages in JDK 9:
Java HotSpot(TM) 64-Bit Server VM warning: Option UseParNewGC was
deprecated in version 9.0 and will likely be removed in a future
release.
Thus, we can and should just remove this flag from the default JVM
options.
Relates #18767
370b198f9f