file descriptor for the given posix mqueue. Export the
timer_oshandle_np() symbol to get ktimer id for the given posix timer.
Requested by: Lewis Donzis <lew@perftech.com>
Reviewed by: jilles
Discussed with: kan
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
is default and caller does not require dedicated thread. timer needs
a dedicated thread to maintain overrun count correctly in notification
context. mqueue and aio can use thread pool to do notification
concurrently, the thread pool has lifecycle control, some threads will
exit if they have idled for a while.