RFR: JDK-8201483 Make it possible to disable JVM features
david.holmes at oracle.com
Thu Apr 12 21:30:08 UTC 2018
On 12/04/2018 11:33 PM, Magnus Ihse Bursie wrote:
> On 2018-04-12 14:15, David Holmes wrote:
>> Hi Magnus,
>> On 12/04/2018 9:39 PM, Magnus Ihse Bursie wrote:
>>> It is currently easy to add new JVM features to the JVM build, but it
>>> is not possible to remove features.
>>> With this change, features can be both added or removed from the
>>> default set. They are added using --with-jvm-features=f1,f2 and
>>> removed using --with-jvm-features=-f1,-f2. The syntax can be
>>> combined, so --with-jvm-features=dtrace,-nmt will enable dtrace but
>>> disable native memory tracking.
>> I need to point out that we have never tested disabling individual VM
>> features likes this. They are either all on, or all off for the
>> minimal VM! There may be implicit dependencies between features.
> Well, I have. :-) However, I don't do that regularly, and changes might
> very well have crept in. As always, if you build something non-standard
> that is not regularly tested, you're on your own.
Feels to me like you've taken away the safety-fence and are encouraging
people to attempt these unsupported configurations. Whether that was
your intent or not.
> In any case, the purpose of this is not so much to disable existing JVM
> features (after all, no one has really been missing this functionality),
> as to pave the way for the upcoming patch for including/excluding
> individual GCs.
Surely a GC selection flag would have sufficed.
>>> I also included some additional code cleanup and fixes, such as
>>> printing the JVM feature set at the summary.
>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8201483
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