X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=src%2Fthreads%2Fthread.c;h=01e8ea42919913a8c5219221c01f52a38f5f1d3e;hb=8abbb333aea445641d967befd3ca477502ea770b;hp=1e5a7d27179e928cb462a813200ed1a8518ccbf4;hpb=546d8bf36bae548643722e1f5d55fd0fcc1c4262;p=pintos-anon

diff --git a/src/threads/thread.c b/src/threads/thread.c
index 1e5a7d2..01e8ea4 100644
--- a/src/threads/thread.c
+++ b/src/threads/thread.c
@@ -46,13 +46,17 @@ static long long idle_ticks;    /* # of timer ticks spent idle. */
 static long long kernel_ticks;  /* # of timer ticks in kernel threads. */
 static long long user_ticks;    /* # of timer ticks in user programs. */
 
+/* Scheduling. */
+#define TIME_SLICE 4            /* # of timer ticks to give each thread. */
+static unsigned thread_ticks;   /* # of timer ticks since last yield. */
+
 static void kernel_thread (thread_func *, void *aux);
 
 static void idle (void *aux UNUSED);
 static struct thread *running_thread (void);
 static struct thread *next_thread_to_run (void);
 static void init_thread (struct thread *, const char *name, int priority);
-static bool is_thread (struct thread *);
+static bool is_thread (struct thread *) UNUSED;
 static void *alloc_frame (struct thread *, size_t size);
 static void schedule (void);
 void schedule_tail (struct thread *prev);
@@ -73,7 +77,7 @@ thread_init (void)
 {
   ASSERT (intr_get_level () == INTR_OFF);
 
-  lock_init (&tid_lock, "tid");
+  lock_init (&tid_lock);
   list_init (&ready_list);
 
   /* Set up a thread structure for the running thread. */
@@ -88,16 +92,18 @@ thread_init (void)
 void
 thread_start (void) 
 {
-  thread_create ("idle", PRI_DEFAULT, idle, NULL);
+  thread_create ("idle", PRI_MAX, idle, NULL);
   intr_enable ();
 }
 
-/* Called by the timer interrupt handler at each timer tick to
-   update statistics. */
+/* Called by the timer interrupt handler at each timer tick.
+   Thus, this function runs in an external interrupt context. */
 void
 thread_tick (void) 
 {
   struct thread *t = thread_current ();
+
+  /* Update statistics. */
   if (t == idle_thread)
     idle_ticks++;
 #ifdef USERPROG
@@ -106,6 +112,10 @@ thread_tick (void)
 #endif
   else
     kernel_ticks++;
+
+  /* Enforce preemption. */
+  if (++thread_ticks >= TIME_SLICE)
+    intr_yield_on_return ();
 }
 
 /* Prints thread statistics. */
@@ -273,11 +283,70 @@ thread_yield (void)
   schedule ();
   intr_set_level (old_level);
 }
+
+/* Sets the current thread's priority to NEW_PRIORITY. */
+void
+thread_set_priority (int new_priority) 
+{
+  thread_current ()->priority = new_priority;
+}
+
+/* Returns the current thread's priority. */
+int
+thread_get_priority (void) 
+{
+  return thread_current ()->priority;
+}
+
+/* Sets the current thread's nice value to NICE. */
+void
+thread_set_nice (int nice UNUSED) 
+{
+  /* Not yet implemented. */
+}
+
+/* Returns the current thread's nice value. */
+int
+thread_get_nice (void) 
+{
+  /* Not yet implemented. */
+  return 0;
+}
+
+/* Returns 100 times the system load average. */
+int
+thread_get_load_avg (void) 
+{
+  /* Not yet implemented. */
+  return 0;
+}
+
+/* Returns 100 times the current thread's recent_cpu value. */
+int
+thread_get_recent_cpu (void) 
+{
+  /* Not yet implemented. */
+  return 0;
+}
 
-/* Idle thread.  Executes when no other thread is ready to run. */
+/* Idle thread.  Executes when no other thread is ready to run.
+
+   The idle thread is initially put on the ready list by
+   thread_start().  It will be scheduled once initially, at which
+   point it initializes idle_thread and immediately blocks.
+   After that, the idle thread never appears in the ready list.
+   It is returned by next_thread_to_run() as a special case when
+   the ready list is empty. */
 static void
 idle (void *aux UNUSED) 
 {
+  /* Initialize idle_thread.
+
+     Until we run for the first time, idle_thread remains a null
+     pointer.  That's okay because we know that, at that point,
+     the ready list has at least one element (the idle thread),
+     so next_thread_to_run() will not attempt to return the idle
+     thread. */
   idle_thread = thread_current ();
 
   for (;;) 
@@ -285,11 +354,20 @@ idle (void *aux UNUSED)
       /* Let someone else run. */
       intr_disable ();
       thread_block ();
-      intr_enable ();
 
-      /* Use CPU `hlt' instruction to wait for interrupt.
-         See [IA32-v2a] "HLT" and [IA32-v3] 7.7. */
-      asm ("hlt");
+      /* Re-enable interrupts and wait for the next one.
+
+         The `sti' instruction disables interrupts until the
+         completion of the next instruction, so these two
+         instructions are executed atomically.  This atomicity is
+         important; otherwise, an interrupt could be handled
+         between re-enabling interrupts and waiting for the next
+         one to occur, wasting as much as one clock tick worth of
+         time.
+
+         See [IA32-v2a] "HLT", [IA32-v2b] "STI", and [IA32-v3a]
+         7.11.1 "HLT Instruction". */
+      asm ("sti; hlt");
     }
 }
 
@@ -314,13 +392,13 @@ running_thread (void)
      down to the start of a page.  Because `struct thread' is
      always at the beginning of a page and the stack pointer is
      somewhere in the middle, this locates the curent thread. */
-  asm ("mov %0, %%esp" : "=g" (esp));
+  asm ("mov %%esp, %0" : "=g" (esp));
   return pg_round_down (esp);
 }
 
 /* Returns true if T appears to point to a valid thread. */
 static bool
-is_thread (struct thread *t) 
+is_thread (struct thread *t)
 {
   return t != NULL && t->magic == THREAD_MAGIC;
 }
@@ -395,6 +473,9 @@ schedule_tail (struct thread *prev)
   /* Mark us as running. */
   cur->status = THREAD_RUNNING;
 
+  /* Start new time slice. */
+  thread_ticks = 0;
+
 #ifdef USERPROG
   /* Activate the new address space. */
   process_activate ();