Description

   This routine stores the value specified in the level argument in
   the "concurrency level" global setting for the calling thread's
   process. Because the Threads Library automatically manages the
   concurrency of all threads in a multithreaded process, it ignores
   this concurrency level value.

   "Concurrency level" is a parameter used to coerce "simple" 2-
   level schedulers into allowing application concurrency. The
   Threads Library supplies the maximum concurrency at all times,
   automatically. It has no need for coercion, and calls pthread_
   setconcurrency() merely to determine the value returned by the
   next call to pthread_getconcurrency().

   The concurrency level value has no effect on the behavior of a
   multithreaded program that uses the Threads Library. This routine
   is provided for Single UNIX Specification, Version 2 source code
   compatibility and has no other effect when called.

   After calling this routine, subsequent calls to the pthread_
   getconcurrency() routine return the same value, until another
   call to pthread_setconcurrency() changes that value.

   The initial concurrency level is zero (0), indicating that the
   Threads Library manages the concurrency level. To indicate in a
   portable manner that the implementation is to resume control of
   concurrency level, call this routine with a level argument of
   zero (0).

   The concurrency level value can be obtained using the pthread_
   getconcurrency() routine.