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

[Tobias Hartmann]

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