first timer alarm implementation

1 files changed, 41 insertions, 4 deletions

diff --git a/pintos-progos/devices/timer.c b/pintos-progos/devices/timer.c
index befaaae..bf78351 100644
--- a/pintos-progos/devices/timer.c
+++ b/pintos-progos/devices/timer.c
@@ -30,11 +30,16 @@ static void busy_wait (int64_t loops);
 static void real_time_sleep (int64_t num, int32_t denom);
 static void real_time_delay (int64_t num, int32_t denom);
 
+/* list of processes waiting for an alarm event
+ * and currently put to sleep */
+static struct list alarm_list;
+
 /* Sets up the timer to interrupt TIMER_FREQ times per second,
    and registers the corresponding interrupt. */
 void
 timer_init (void) 
 {
+  list_init (&alarm_list);
   pit_configure_channel (0, 2, TIMER_FREQ);
   intr_register_ext (0x20, timer_interrupt, "8254 Timer");
 }
@@ -89,11 +94,26 @@ timer_elapsed (int64_t then)
 void
 timer_sleep (int64_t ticks) 
 {
-  int64_t start = timer_ticks ();
+  struct thread *t = thread_current ();
+  enum intr_level old_level;
 
-  ASSERT (intr_get_level () == INTR_ON);
-  while (timer_elapsed (start) < ticks) 
-    thread_yield ();
+  /* nothing to sleep here */
+  if (ticks <= 0)
+    return;
+
+  t->alarm_tick = timer_ticks () + ticks;
+
+  /* add thread to alarm list
+   * disable interrupts as this is critical */
+  old_level = intr_disable ();
+  ASSERT (t->status == THREAD_RUNNING);
+  list_push_back (&alarm_list, &t->elem);
+
+  /* block the thread */
+  thread_block();
+
+  /* restore interrupt */
+  intr_set_level (old_level);
 }
 
 /* Sleeps for approximately MS milliseconds.  Interrupts must be
@@ -170,8 +190,25 @@ timer_print_stats (void)
 static void
 timer_interrupt (struct intr_frame *args UNUSED)
 {
+  struct list_elem *el, *next;
+
   ticks++;
   thread_tick ();
+
+  /* check for threads waiting for an alarm event */
+  for (el = list_begin (&alarm_list); el != list_end (&alarm_list); el = next)
+    {
+      struct thread *t = list_entry (el, struct thread, elem);
+      if (t->alarm_tick == timer_ticks ())
+        {
+          next = list_remove (el);
+          /* unblock must be called AFTER removing,
+           * as thread_unblock() will reuse thread.elem */
+          thread_unblock (t);
+        }
+      else
+        next = list_next (el);
+    }
 }
 
 /* Returns true if LOOPS iterations waits for more than one timer