RTEMS: race between recvfrom()/accept() and close() results in stuck threads

[mdavidsaver]

Running testChannelAccess on RTEMS (for the first time?) leaves worker threads hung in recvfrom() and accept(). On investigation I find that this results if a socket is close()d while concurrent accept() or recvfrom() is in progress.

[mdavidsaver]

The current shutdown sequence:

shutdown(socket, SHUT_RDWR);
close(socket);
thread.exitWait()

The problem with RTEMS can be avoided with:

shutdown(socket, SHUT_RDWR);
thread.exitWait()
close(socket);

However, this presents problems on targets other than Linux and RTEMS where shutdown() doesn't interrupt either accept() or recvfrom().

cf. epics-base/epics-base#30