kernel: Add z_thread_wake_joiners() utility

POSIX has a somewhat odd behavior that when you call
pthread_detach()[1], it is supposed to synchronously wake up anyone
currently joining the thread.  That isn't a Zephyr kernel behavior[2],
so it needs to be exposed.

The implementation is as simple as it sounds.  This is minimal: we
don't try to keep any state around to inform the k_thread_join() call
whether the thread actually exited or if this new function was used.
That has to be provided by the outer layers (pthreads already do
this).

[1] Which tells the OS/platform that it can clean the thread up as
soon as it exits and doesn't have to keep it around as a zombie until
someone calls pthread_join() on it.

[2] Because... why!?  Not needing to keep a thread around for joiners
isn't the same thing as disallowing joins!

Signed-off-by: Andy Ross <[email protected]>

Author: andyross

kernel/include/ksched.h

@@ -64,6 +64,7 @@ void z_ready_thread(struct k_thread *thread);
 void z_requeue_current(struct k_thread *curr);
 struct k_thread *z_swap_next_thread(void);
 void z_thread_abort(struct k_thread *thread);
+void z_thread_wake_joiners(struct k_thread *thread);
 
 static inline void z_pend_curr_unlocked(_wait_q_t *wait_q, k_timeout_t timeout)
 {

kernel/sched.c

@@ -1729,6 +1729,13 @@ static void end_thread(struct k_thread *thread)
 	}
 }
 
+void z_thread_wake_joiners(struct k_thread *thread)
+{
+	LOCKED(&sched_spinlock) {
+		unpend_all(&thread->join_queue);
+	}
+}
+
 void z_thread_abort(struct k_thread *thread)
 {
 	k_spinlock_key_t key = k_spin_lock(&sched_spinlock);