A thread that has been completed without thread_join/2 being called on it is partly reclaimed: the Prolog stacks are released and the C thread is destroyed. A small data structure representing the exit status of the thread is retained until thread_join/2 is called on the thread. Defined values for Status are:

true

The goal has been proven successfully.

false

The goal has failed.

exception(Term)

The thread is terminated on an exception. See print_message/2 to turn system exceptions into readable messages.

exited(Term)

The thread is terminated on thread_exit/1 using the argument Term.

Note that the pthread primitive pthread_join() cannot be interrupted. Some systems provide pthread_timedjoin_np(). If this is provided thread_join/2 is implemented as a loop of timed joins with a 0.25 sec timeout while signals are being tested after each timeout. Such systems allow combining thread_join/2 with call_with_time_limit/2 as well as signalling threads blocked in thread_join/2 using thread_signal/2.