Availability:built-in
thread_setconcurrency(-Old,
+New)Determine the concurrency of the process,
which is defined as the maximum number of concurrently active threads.
`Active' here means they are using CPU time. This option is provided if
the thread implementation provides pthread_setconcurrency(). Solaris is
a typical example of this family. On other systems this predicate
unifies Old to 0 (zero) and succeeds silently.