+/* Low priority thread L acquires a lock, then blocks downing a
+ semaphore. Medium priority thread M then blocks waiting on
+ the same semaphore. Next, high priority thread H attempts to
+ acquire the lock, donating its priority to L.
+
+ Next, the main thread ups the semaphore, waking up L. L
+ releases the lock, which wakes up H. H "up"s the semaphore,
+ waking up M. H terminates, then M, then L, and finally the
+ main thread.
+
+ Written by Godmar Back <gback@cs.vt.edu>. */
+
+#include <stdio.h>
+#include "tests/threads/tests.h"
+#include "threads/init.h"
+#include "threads/synch.h"
+#include "threads/thread.h"
+
+struct lock_and_sema
+ {
+ struct lock lock;
+ struct semaphore sema;
+ };
+
+static thread_func l_thread_func;
+static thread_func m_thread_func;
+static thread_func h_thread_func;
+
+void
+test_priority_donate_sema (void)
+{
+ struct lock_and_sema ls;
+
+ /* This test does not work with the MLFQS. */
+ ASSERT (!enable_mlfqs);
+
+ /* Make sure our priority is the default. */
+ ASSERT (thread_get_priority () == PRI_DEFAULT);
+
+ lock_init (&ls.lock);
+ sema_init (&ls.sema, 0);
+ thread_create ("low", PRI_DEFAULT + 1, l_thread_func, &ls);
+ thread_create ("med", PRI_DEFAULT + 3, m_thread_func, &ls);
+ thread_create ("high", PRI_DEFAULT + 5, h_thread_func, &ls);
+ sema_up (&ls.sema);
+ msg ("Main thread finished.");
+}
+
+static void
+l_thread_func (void *ls_)
+{
+ struct lock_and_sema *ls = ls_;
+
+ lock_acquire (&ls->lock);
+ msg ("Thread L acquired lock.");
+ sema_down (&ls->sema);
+ msg ("Thread L downed semaphore.");
+ lock_release (&ls->lock);
+ msg ("Thread L finished.");
+}
+
+static void
+m_thread_func (void *ls_)
+{
+ struct lock_and_sema *ls = ls_;
+
+ sema_down (&ls->sema);
+ msg ("Thread M finished.");
+}
+
+static void
+h_thread_func (void *ls_)
+{
+ struct lock_and_sema *ls = ls_;
+
+ lock_acquire (&ls->lock);
+ msg ("Thread H acquired lock.");
+
+ sema_up (&ls->sema);
+ lock_release (&ls->lock);
+ msg ("Thread H finished.");
+}