The lock functions don't really need to disable interrupts themselves,

since they're protected by the semaphore.
Thanks to Godmar Back for reporting this.

diff --git a/doc/threads.texi b/doc/threads.texi
index 432cb2668224dab21a7be7164d476324cf2ad63d..d1ff66640cd05f9d428375bf6bf0bd91958357ea 100644 (file)
--- a/doc/threads.texi
+++ b/doc/threads.texi
@@ -328,9 +328,10 @@ timer ticks or input events.  Turning off interrupts also increases the
 interrupt handling latency, which can make a machine feel sluggish if
 taken too far.
 
-You may need to add or modify code where interrupts are already
-disabled, such as in @func{sema_up} or @func{sema_down}.  You should
-still try to keep this code as short as you can.
+The synchronization primitives themselves in @file{synch.c} are
+implemented by disabling interrupts.  You may need to increase the
+amount of code that runs with interrupts disabled here, but you should
+still try to keep it to a minimum.
 
 Disabling interrupts can be useful for debugging, if you want to make
 sure that a section of code is not interrupted.  You should remove

diff --git a/src/threads/synch.c b/src/threads/synch.c
index 5ec14abf8d4dfa11851e02917a1d030540a560f0..c2764bc38d1cdb3b47efb0f0a43f8d694d493947 100644 (file)
--- a/src/threads/synch.c
+++ b/src/threads/synch.c
@@ -192,16 +192,12 @@ lock_init (struct lock *lock)
 void
 lock_acquire (struct lock *lock)
 {
-  enum intr_level old_level;
-
   ASSERT (lock != NULL);
   ASSERT (!intr_context ());
   ASSERT (!lock_held_by_current_thread (lock));
 
-  old_level = intr_disable ();
   sema_down (&lock->semaphore);
   lock->holder = thread_current ();
-  intr_set_level (old_level);
 }
 
 /* Tries to acquires LOCK and returns true if successful or false
@@ -213,18 +209,14 @@ lock_acquire (struct lock *lock)
 bool
 lock_try_acquire (struct lock *lock)
 {
-  enum intr_level old_level;
   bool success;
 
   ASSERT (lock != NULL);
   ASSERT (!lock_held_by_current_thread (lock));
 
-  old_level = intr_disable ();
   success = sema_try_down (&lock->semaphore);
   if (success)
     lock->holder = thread_current ();
-  intr_set_level (old_level);
-
   return success;
 }
 
@@ -236,15 +228,11 @@ lock_try_acquire (struct lock *lock)
 void
 lock_release (struct lock *lock) 
 {
-  enum intr_level old_level;
-
   ASSERT (lock != NULL);
   ASSERT (lock_held_by_current_thread (lock));
 
-  old_level = intr_disable ();
   lock->holder = NULL;
   sema_up (&lock->semaphore);
-  intr_set_level (old_level);
 }
 
 /* Returns true if the current thread holds LOCK, false