RFR: 8189276: Make SuspendibleThreadSet and related code available to other GCs

[David Holmes]

+1 on not exposing this to runtime, but leave it as GC.

David

On 18/10/2017 7:10 AM, Roman Kennke wrote:
> 
>> The SuspendibleThreadSet API for synchronizing any non-Java thread 
>> with safepoints currently resides under gc/g1. It is very useful for 
>> other GCs too (in particular, Shenandoah does use it too), so I wanted 
>> to move it to a common location like gc/common. Then Kim Barrett 
>> commented that it might actually be useful for other threads outside 
>> GC land and to put it under runtime/. So I did:
>>
>> http://cr.openjdk.java.net/~rkennke/8189276/webrev.00/ 
>> <http://cr.openjdk.java.net/%7Erkennke/8189276/webrev.00/>
>>
>> I also added a generic hook to call the STS from safepoint 
>> sync/desync, which is consequently used by G1 now. In other words, the 
>> CollectedHeap API that Erik Ö introduced is no longer used by G1. Only 
>> CMS still uses that API because it has its own way to sync with 
>> safepoints. I filed another bug 
>> <https://bugs.openjdk.java.net/browse/JDK-8189364> for this. Although 
>> I have my doubt it will ever be fixed. This seems to have been very 
>> carefully evolved (to put it positive), and the risk of breaking it is 
>> relatively high, and thus doesn't seem worth the struggle to make it 
>> fit the STS.
>>
>> Issue:
>> https://bugs.openjdk.java.net/browse/JDK-8189276
>>
>> What do you think? Ok to go in?
>>
> Replying to myself here.
> I must admit that I am a bit reluctant to expose it to runtime/ unless 
> there's a specific need for it. So maybe go back to the original plan to 
> move it into gc/common and leave all the rest alone for now? What do 
> others think?
> 
> Roman