RFR [9] 8148117: Move sun.misc.Cleaner to jdk.internal.ref

[Alan Bateman]

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