This is the xr threads package.

- Only implemented for sparc; this should be trivial to fix.
- Only for SunOS 4.0; this will be less trivial to fix, because of reliance
    on mmap and semaphores.
- A lot of Unix I/O stuff is included here; this ought to be broken out into
    a separate component

Demers, October 24, 1988 9:46:13 am PDT

TODO:

January 3, 1989 12:44:37 pm PST

  - In UIOPrivate.h, there's one IOPOrder per thread.  I think this may be
  unnecessary -- in most cases the IOPOrders can be stack-frame-allocated,
  and in the remaining cases they need to be heap allocated and garbage-
  collected anyway.

