RFR: 8234662: Sweeper should keep current nmethod alive before yielding for ICStub refills

[Stefan Karlsson]

Looks good.

StefanK

On 2019-11-22 16:03, erik.osterlund at oracle.com wrote:
> Hi,
> 
> Today, when GCs scan the stack, all nmethods roots found from threads 
> are nmethods that have gone through an nmethod entry barrier (in the 
> case of concurrent class unloading), except the super special sweeper 
> nmethod that is currently being processed when it runs out of ICStubs 
> and need to safepoint to refill ICStubs, which with the fantastic 
> safepoint coalescing optimization that we all know and love, can get 
> fused into a GC safepoint, which will find the sweeper nmethod and be 
> confused why it has not gone through an entry barrier before it yielded 
> to the safepoint like everyone else.
> 
> This causes some headache, and I would like to harmonize this better by 
> simply calling the nmethod entry barrier on that nmethod in the sweeper, 
> before yielding to the safepoint. Then there is no need to treat it as a 
> special case.
> 
> Bug:
> https://bugs.openjdk.java.net/browse/JDK-8234662
> 
> Webrev:
> http://cr.openjdk.java.net/~eosterlund/8234662/webrev.00/
> 
> Thanks.
> /Erik