fix sema_up() and hence the priority-sema testcase => 2/18 failed

+ some minor documentation and cleanup stuff

2 files changed, 7 insertions, 15 deletions

diff --git a/threads/synch.c b/threads/synch.c
index 92008ef..2cb4805 100644
--- a/threads/synch.c
+++ b/threads/synch.c
@@ -116,24 +116,21 @@ void
 sema_up (struct semaphore *sema) 
 {
   enum intr_level old_level;
-  bool yield = false;
+  struct thread *t = NULL;
 
   ASSERT (sema != NULL);
 
   old_level = intr_disable ();
-  if (!list_empty (&sema->waiters))
+  while (!list_empty (&sema->waiters))
   {
-    struct thread *t = list_entry (list_pop_front (&sema->waiters),
-        struct thread, elem);
+    t = list_entry (list_pop_front (&sema->waiters), struct thread, elem);
     thread_unblock (t);
-    /* thread_unblock() doesn't yield so check if there's a need */
-    if (t->priority > thread_current ()->priority)
-      yield = true;
   }
   sema->value++;
   intr_set_level (old_level);
 
-  if (yield)
+  /* thread_unblock() doesn't yield so check if there's a need */
+  if (t != NULL && t->priority > thread_current ()->priority)
     thread_yield();
 }
 
@@ -228,8 +225,6 @@ lock_acquire (struct lock *lock)
 
   if (lock->holder != NULL)
   {
-    //printf("[%d] acquire: lock=%p prio=%d\n", cur->tid, lock, cur->priority);
-
     /* check for a possible priority donation */
     if (cur->priority > lock->priority)
     {
@@ -291,18 +286,15 @@ lock_release (struct lock *lock)
   ASSERT (lock_held_by_current_thread (lock));
 
   lock->holder = NULL;
-  //lock->priority = we don't care as the next lock_acquire ()-call does
+  //lock->priority = we don't care as the next lock_acquire()-call does
   sema_up (&lock->semaphore);
 
   /* we don't hold the lock any longer so remove it from the lock list */
   list_remove (&lock->elem);
 
   if (list_empty (&cur->locks))
-  {
-    //printf("[%d] restoring prio from %d to %d\n", cur->tid, cur->priority, cur->saved_priority);
     /* we don't hold another lock so restore our base priority */
     thread_donation_pass_back ();
-  }
   else
   {
     /* we still hold at least one lock so change our priority to the priority of the lock */
diff --git a/threads/thread.h b/threads/thread.h
index 8bc6512..8cfafe6 100644
--- a/threads/thread.h
+++ b/threads/thread.h
@@ -110,7 +110,7 @@ struct thread
 
     int is_donated;                     /* flag if threads priority has been donated by another thread */
     int saved_priority;                 /* saved base priority in case of priority dontation */
-    struct list locks;                  /* list of locks we currently hold */
+    struct list locks;                  /* list of locks the thread currently holds */
   };
 
 /* If false (default), use round-robin scheduler.