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

Vladimir Kozlov vladimir.kozlov at oracle.com
Fri Aug 28 02:51:01 UTC 2015

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.


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

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