The thr_join() function suspends processing of
the calling thread until the target thread completes.
The thread argument must be a member of the current
process and cannot be a detached thread. See thr_create(3THR).
If two or more threads wait for the same thread to complete, all will
suspend processing until the thread has terminated, and then one thread
will return successfully and the others will return with an error of ESRCH. The thr_join() function will not block
processing of the calling thread if the target thread
has already terminated.
If a thr_join() call returns successfully with
a non-null status argument, the value passed
to thr_exit(3THR) by the terminating thread
will be placed in the location referenced by status.
If the target thread ID is 0, thr_join() finds
and returns the status of a terminated undetached thread in the process.
If no such thread exists, it suspends processing of the calling thread until
a thread for which no other thread is waiting enters that state, at which
time it returns successfully, or until all other threads in the process
are either daemon threads or threads waiting in thr_join(),
in which case it returns EDEADLK. See NOTES.
If departed is not NULL, it points to a location that is set to the ID of the terminated
thread if thr_join() returns successfully.