Re: RFR (XS) 8066679: jvmtiRedefineClasses.cpp assert cache ptrs must match

[Daniel D. Daugherty]

On 3/25/15 7:16 PM, serguei.spit...@oracle.com wrote:

Please, review the fix for:
  https://bugs.openjdk.java.net/browse/JDK-8066679


Open hotspot webrev:

http://cr.openjdk.java.net/~sspitsyn/webrevs/2015/hotspot/8066679-JVMTI-cache.1/

src/share/vm/prims/jvmtiRedefineClasses.cpp
    I concur that the old assertions are bad. They assume that
    the cached class file bytes on the scratch_class must match
    the cached class file bytes on the target class. That's a
    valid assumption in a RedefineClasses() only world, but that's
    not true when RetransformClasses() is used.

This will be hard to test. I think the race can only happen
on the first retransform of a class. If you have two parallel
retransform threads, both see that there are no cached bytes
so both cache the initial bytes and then both have to update
the cached bytes pointer at about the same time... Very hard
to do...

Thumbs up.

Dan

Summary:

There can be multiple concurrent RetransformClasses calls on different threads. So that, the assert "cache ptrs must match" is incorrect as it was based on wrong assumptions. The fix removes two related asserts and also frees the scratch_class cached_class_file_bytes

  if it is necessary to avoid leaking the memory.


Testing:
  In progress: nsk redefine classes tests, JTREG java/lang/instrument


Thanks,
Serguei