RFR: JDK-8201483 Make it possible to disable JVM features

[Magnus Ihse Bursie]

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.

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.

/Magnus

>
> David
>
>> 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
>> WebRev: 
>> http://cr.openjdk.java.net/~ihse/JDK-8201483-disable-JVM-features/webrev.01
>>