Hi Alan, Calling sun.nio directly from java.lang seemed a bit dodgy to me, which is why I proposed some type of exit hook (maybe I overthought this?). But that’d be OK, could make this change a lot simpler. :-) And, yes, I came across the issue of not being able to query whether a ThreadLocal exists on a Thread when I implemented my prototype. Which is why I think introducing an exit hook on ThreadLocal, instead of Thread, is probably the better approach (it will only be called if the ThreadLocal exists).
Tony ————— Tony Printezis | @TonyPrintezis | tprinte...@twitter.com On April 6, 2018 at 4:02:56 AM, Alan Bateman (alan.bate...@oracle.com) wrote: On 05/04/2018 22:45, Tony Printezis wrote: > Hi all, > > We recently hit another interesting issue with the NIO thread-local > DirectByteBuffer cache. One of our services seems to create and drop > threads at regular intervals. I assume this is due to a thread pool > dynamically resizing itself. > > Let's say a thread starts, lives long enough for its Thread object to be > promoted to the old gen (along with its cached direct buffer), then exits. > This will result in its cached direct buffer(s) being unreachable in the > old gen and will only be reclaimed after the next full GC / concurrent GC > cycle. > Right, if a short lived thread does I/O with a buffer backed by an array in the heap then any direct buffers in its thread local cache won't be freed until there is a GC and reference processing. It's something that I've prototyped a few times and always leaned towards not exposing anything in the API, instead just hooking into the thread exit to clear the buffer cache. One thing to watch out for is that the buffer cache may not exist (as the thread didn't do any I/O with heap buffers) so you'll end up creating (an empty) buffer cache at thread exit. That is benign of course but still unsettling to have additional code executing at this time. -Alan
