[9] RFR(S): 8134493: Cleaning inline caches of unloaded nmethods should be done in sweeper

[Vladimir Kozlov]

CodeCache::gc_epilogue() could be optimized more. When 
needs_cache_clean() is false we need to execute loop only in debug VM.

Otherwise it looks good.

Thanks,
Vladimir

On 8/27/15 12:10 AM, Tobias Hartmann wrote:
> Hi,
>
> please review the following patch.
>
> https://bugs.openjdk.java.net/browse/JDK-8134493
> http://cr.openjdk.java.net/~thartmann/8134493/webrev.00/
>
> Problem:
> This is a follow up on JDK-8075805 [1] which modified CodeCache::gc_epilogue() to clean the ICs of unloaded nmethods as well. The problem is that this code is executed at a safepoint and may affect safepoint duration. The other changes of JDK-8134493 are fine.
>
> Solution:
> We do the cleaning of unloaded nmethods at the unloaded -> zombie transition in the sweeper. I also modified nmethod::cleanup_inline_caches() to not emit any transition stubs if the nmethod is already dead.
>
> As Martin Doerr pointed out in another thread, we have to be careful with accessing CompiledIC::cached_metadata() of unloaded nmethods. For example, the following scenario may happen (IC of A references B):
>
>      state of A       state of B
> -------------------------------
>      not-entrant
> S   [not-on-stack]
> S   zombie
> 	             unloaded
>
> Now the IC of A still references the unloaded nmethod B and is_call_to_compiled() will access the unloaded metadata. I fixed this by checking caller->is_alive().
>
> Thanks,
> Tobias
>
> [1] https://bugs.openjdk.java.net/browse/JDK-8075805
>
>