libthreads: perform all scheduling/model-checking from master thread

To keep all user-space actions under control, we should perform all scheduling
and model-checking from the main system thread. This pushes some of the
thread_yield() logic to a system function (as desired).

diff --git a/libthreads.c b/libthreads.c
index 892d784587b7c00fa22083bde526567729326170..4233c0e306bdd94d8be557f58835c3be89eb20de 100644 (file)
--- a/libthreads.c
+++ b/libthreads.c
@@ -61,9 +61,8 @@ int thread_yield(void)
 
        DBG();
        old = thread_current();
-       model->scheduler->add_thread(old);
-       next = model->scheduler->next_thread();
-       DEBUG("(%d, %d)\n", old->index, next->index);
+       old->state = THREAD_READY;
+       next = model->system_thread;
        return thread_swap(old, next);
 }
 
@@ -74,17 +73,38 @@ static void thread_dispose(struct thread *t)
        stack_free(t->stack);
 }
 
-static void thread_wait_finish(void)
+/*
+ * Return 1 if found next thread, 0 otherwise
+ */
+static int thread_system_next(void)
 {
        struct thread *curr, *next;
 
+       curr = thread_current();
+       if (curr) {
+               if (curr->state == THREAD_READY)
+                       model->scheduler->add_thread(curr);
+               else if (curr->state == THREAD_RUNNING)
+                       /* Stopped while running; i.e., completed */
+                       thread_dispose(curr);
+               else
+                       DEBUG("ERROR: current thread in unexpected state??\n");
+       }
+       next = model->scheduler->next_thread();
+       if (next)
+               next->state = THREAD_RUNNING;
+       DEBUG("(%d, %d)\n", curr ? curr->index : -1, next ? next->index : -1);
+       if (!next)
+               return 1;
+       return thread_swap(model->system_thread, next);
+}
+
+static void thread_wait_finish(void)
+{
+
        DBG();
 
-       do {
-               if ((curr = thread_current()))
-                       thread_dispose(curr);
-               next = model->scheduler->next_thread();
-       } while (next && !thread_swap(model->system_thread, next));
+       while (!thread_system_next());
 }
 
 int thread_create(struct thread *t, void (*start_routine), void *arg)