Description

   This routine obtains and returns the value of 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.

   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.

   The initial concurrency level is zero (0), indicating that the
   Threads Library controls the concurrency level.

   The concurrency level can be set using the pthread_
   setconcurrency() routine.