On 25/01/2016 15:27, Peter Levart wrote:
But let me ask something. Doesn't GC processing require (at least in
some phases) that user threads be stopped in a safepoint? What happens
when a user thread is blocked by kernel on memory access? Such thread
can't be stopped in a safepoint. Safepoint can't begin, so GC can't
proceed and therefore can't promote objects to old generation at that
time. Am I right? If yes, then time does not pass for objects while a
user thread is blocked on memory access, so they won't get promoted to
old gen any time sooner after the user thread is unblocked.
With memory mapping then it's very possible that a memory access to
stall waiting for pages to be faulted in. So yes, I assume any
STW/safepoint is going to be stall. On the other hand then threads doing
file or socket I/O on these buffers will be in native (maybe blocked,
maybe not) and so aren't an issue. They will safepoint on return or if
they attempt to re-enter.
-Alan
