> On Mar 21, 2016, at 8:20 AM, Per Liden <per.li...@oracle.com> wrote: > > Hi Peter & David, > > (Resurrecting an old thread here...) > > On 2014-01-22 03:19, David Holmes wrote: >> Hi Peter, >> >> On 22/01/2014 12:00 AM, Peter Levart wrote: >>> Hi, David, Kalyan, >>> >>> Summing up the discussion, I propose the following patch for >>> ReferenceHandler: >>> >>> http://cr.openjdk.java.net/~plevart/jdk9-dev/OOMEInReferenceHandler/webrev.01/ >>> >> >> I can live with it, though it maybe that once Cleaner has been preloaded >> instanceof can no longer throw OOME. Can't be 100% sure. And there's >> some duplication/verbosity in the commentary that could be trimmed down :) > > While investigating a Reference pending list issue on the GC side of things I > looked at the ReferenceHandler thread and noticed something which made me > uneasy. The fix for JDK-8022321 added pre-loading of the Cleaer class to > avoid OMME, but also moved the "instanceof Cleaner" inside the try/catch with > a comment that it "sometimes" can throw an OOME. I understand this was done > because we're not 100% sure if a OOME can still happen here, despite the > pre-loading. > > However, if it can throw an OOME that means it's allocating, which in turn > means it can provoke a GC. If that happens, it looks to me like we have a bug > here. The ReferenceHandler thread is not allowed to provoke a GC while it's > holding on to the pending list lock, since the pending list might be updated > during a GC and "pending = r.discovered" will than overwrite something other > than "r", silently dropping any newly discovered References which will never > be discovered by the the GC again. > > On the other hand, if an OOME can never happen (i.e. no GC) here then we're > good the comment is just incorrect. The instanceof check could be moved out > of the try/catch block again, like it was prior to this change, just to make > it obvious that we will not be able to cause new allocations inside the > critical section. Or at a minimum, the comment saying OOME can still happen > should be adjusted. > > Thoughts? > > thanks, > Per > > Btw, to the best of my knowledge, the pre-loading of Cleaner should avoid any > GC activity from instanceof, but I can't say that am a 100% sure either.
Per - I think you are raising the same issue as discussed in https://bugs.openjdk.java.net/browse/JDK-8055232.
