CMA threads usage?

[h]

I have looked at the CMA threads package as a potential means to 
execute multi-threaded software under Unix.  I need threads to have
the following semantics:  a thread executing a blocking system call
(eg: read(...)) should only block itself and allow other threads to
continue to execute, and preemptive scheduling of threads allowing
the currently executing thread to be preempted if a higher priority
thread becomes ready.  CMA threads do not have this functionality.

My questions are:
  How are users of CMA threads achieving parallelism in their code
  when blocking system calls are neccessary or desirable?

  Are alternate libraries providing non-blocking versions of the
  system calls used that are compatible with CMA's model of threads?

  Do you HAVE to resort to using O_NDELAY and busy wait loops when
  to avoid blocking system calls?

  Etc?

Any info or suggestions would be appreciate, thanks.
-- 
----------
Michael L. Kornegay,
  kornegay at oiscola.columbia.ncr.com