post-5.1: rthreads


uthreads (until 5.1) have shortcomings
one process, one CPU
all fds are put in nonblocking mode, some side-effects
some syscalls don't work 100% correctly (kevent, open of FIFOs)

rthreads: 1:1 kernel model
threads of a single process spread over CPUs
no more behind-the-scenes nonblocking-mode for fds
problems with blocking syscalls gone