Merge branch 'task1/themis/priority-donation' into 'task1/priority-donation'

Merge task1/themis/priority-donation into task1/priority-donation

See merge request lab2425_autumn/pintos_22!13

src/threads/synch.c

@@ -194,11 +194,12 @@ lock_init (struct lock *lock)
   sema_init (&lock->semaphore, 1);
 }
 
-/* Allows for the donor to donate its priority to donee, iteratively
+/* Current thread donates its priority to donee, iteratively
    propagating the donation in the case of chains in the wait-for graph.
    Also keeps track of the donation by updating the donors list. */
 static void
-donate_priority (struct thread *donor, struct thread *donee) {
+donate_priority (struct thread *donee) {
+  struct thread *donor = thread_current ();
   list_push_back (&donee->donors_list, &donor->donor_elem);
   
   while (donee != NULL)
@@ -209,17 +210,26 @@ donate_priority (struct thread *donor, struct thread *donee) {
       if (donor->priority <= donee->priority)
           break;
 
-      donee->priority = donor->priority;
-
       /* Also stop propagation of donation once a donee is reached with
          no donees of its own (sink node in WFG). */
       if (donee->waiting_lock == NULL)
-        donee = NULL;
+        {
+          /* Only the sink node of the WFG isn't waiting for a lock and
+             could be on the ready list. Thus, as its priority changed,
+             it must be reinserted into the list. */
+          enum intr_level old_level = intr_disable ();
+          donee->priority = donor->priority;
+          ready_list_reinsert (donee);
+          intr_set_level (old_level);
+          
+          donee = NULL;
+        }
       else
-        donee = donee->waiting_lock->holder;
+        {
+          donee->priority = donor->priority;
+          donee = donee->waiting_lock->holder;
+        }
     }
-
-  ready_list_reorder ();
 }
 
 /* Acquires LOCK, sleeping until it becomes available if
@@ -244,7 +254,7 @@ lock_acquire (struct lock *lock)
   if (lock->holder != NULL)
     {
       t->waiting_lock = lock;
-      donate_priority (t, lock->holder);
+      donate_priority (lock->holder);
     }
 
   sema_down (&lock->semaphore);

src/threads/thread.c

@@ -465,10 +465,20 @@ thread_get_recent_cpu (void)
   return 0;
 }
 
+/* Reinsert thread t into the ready list at its correct position
+   in descending order of priority. Used when this thread's priority
+   may have changed. Must be called with interrupts disabled. */
 void
-ready_list_reorder (void)
+ready_list_reinsert (struct thread *t)
 {
-  list_sort (&ready_list, priority_more, NULL);
+  ASSERT (intr_get_level () == INTR_OFF);
+
+  /* If the thread isn't ready to run, do nothing. */
+  if (t->status != THREAD_READY)
+    return;
+
+  list_remove (&t->elem);
+  list_insert_ordered (&ready_list, &t->elem, priority_more, NULL);
 }
 
 /* Idle thread.  Executes when no other thread is ready to run.
@@ -558,7 +568,7 @@ init_thread (struct thread *t, const char *name, int priority)
   t->stack = (uint8_t *) t + PGSIZE;
   t->base_priority = priority;
   t->magic = THREAD_MAGIC;
-
+  
   list_init (&t->donors_list);
   t->priority = t->base_priority;
   t->waiting_lock = NULL;

src/threads/thread.h

@@ -151,6 +151,6 @@ void thread_set_nice (int);
 int thread_get_recent_cpu (void);
 int thread_get_load_avg (void);
 
-void ready_list_reorder (void);
+void ready_list_reinsert (struct thread *t);
 
 #endif /* threads/thread.h */