On Tue, 15 Feb 2022 06:31:46 GMT, Chris Plummer <cjplum...@openjdk.org> wrote:
>> Zhengyu Gu has updated the pull request incrementally with one additional >> commit since the last revision: >> >> David and Chris' comments > > src/jdk.jdwp.agent/share/native/libjdwp/classTrack.c line 65: > >> 63: * handler may acquire the same monitor(s), e.g. classTrackLock in >> cbTrackingObjectFree(), >> 64: * which can lead to deadlock. >> 65: */ > > The debug agent does a lot alloc/dealloc calls while processing JVMTI events > and holding locks. So the question is why this is not problematic other than > this classTrackLock issue. I believe the answer is that > cbTrackingObjectFree() is unique in that it is handled outside of the debug > agent's normal event handling code, which is serialized. > cbTrackingObjectFree() is called so the debug agent can maintain a list of > loaded classes, and is not an event that gets passed on to the debugger like > most JVMTI events are. So we have a case here where classTrackLock can be > grabbed by both "typical" JVMTI event handling code via the > classTrack_processUnloads() call, and then this special > cbTrackingObjectFree() event handling. > > I think having this comment here doesn't help the reader of the code below > unless they somehow read the comment first and then recognized it's > application in the code below. At the very least the code below should > tersely state while the lock is being released, and then refer to this > comment for details. I moved comments inside `classTrack_processUnloads()`, let me know if you prefer other places. ------------- PR: https://git.openjdk.java.net/jdk/pull/7461
