Contention Scope
Support for contention scope is optional. The Threads Module determines whether contention scope is supported by testing for the definition of the macro _POSIX_THREAD_PRIORITY_SCHEDULING.
Linux does not support process-scope threads because each Linux thread is a separate Unix process. Therefore, all threads have a fixed contention scope of RW_THR_SYSTEM_SCOPE.
You may query the contention scope and freely set it to RW_THR_SYSTEM_SCOPE (although it is already set to that by default); but any attempt to change the scope to RW_THR_PROCESS_SCOPE produces an exception.