X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?p=pintos-anon;a=blobdiff_plain;f=src%2Fthreads%2Fthread.c;h=d68c123fb2476420d09557f4f52d4a6fb12949f4;hp=5229aef34d013b5bfd8bcd9c09a2983637018dc9;hb=09fa5c11aff62bd728d4fe8de28a7abaf252fed3;hpb=3f521b71eaf97c531bfa671b3aa2b9b971a37499

diff --git a/src/threads/thread.c b/src/threads/thread.c
index 5229aef..d68c123 100644
--- a/src/threads/thread.c
+++ b/src/threads/thread.c
@@ -7,10 +7,10 @@
 #include "threads/flags.h"
 #include "threads/interrupt.h"
 #include "threads/intr-stubs.h"
-#include "threads/mmu.h"
 #include "threads/palloc.h"
 #include "threads/switch.h"
 #include "threads/synch.h"
+#include "threads/vaddr.h"
 #ifdef USERPROG
 #include "userprog/process.h"
 #endif
@@ -24,6 +24,10 @@
    that are ready to run but not actually running. */
 static struct list ready_list;
 
+/* List of all processes.  Processes are added to this list
+   when they are first scheduled and removed when they exit. */
+static struct list all_list;
+
 /* Idle thread. */
 static struct thread *idle_thread;
 
@@ -50,6 +54,11 @@ static long long user_ticks;    /* # of timer ticks in user programs. */
 #define TIME_SLICE 4            /* # of timer ticks to give each thread. */
 static unsigned thread_ticks;   /* # of timer ticks since last yield. */
 
+/* If false (default), use round-robin scheduler.
+   If true, use multi-level feedback queue scheduler.
+   Controlled by kernel command-line option "-o mlfqs". */
+bool thread_mlfqs;
+
 static void kernel_thread (thread_func *, void *aux);
 
 static void idle (void *aux UNUSED);
@@ -59,7 +68,7 @@ static void init_thread (struct thread *, const char *name, int priority);
 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);
+void thread_schedule_tail (struct thread *prev);
 static tid_t allocate_tid (void);
 
 /* Initializes the threading system by transforming the code
@@ -71,7 +80,10 @@ static tid_t allocate_tid (void);
 
    After calling this function, be sure to initialize the page
    allocator before trying to create any threads with
-   thread_create(). */
+   thread_create().
+
+   It is not safe to call thread_current() until this function
+   finishes. */
 void
 thread_init (void) 
 {
@@ -79,6 +91,7 @@ thread_init (void)
 
   lock_init (&tid_lock);
   list_init (&ready_list);
+  list_init (&all_list);
 
   /* Set up a thread structure for the running thread. */
   initial_thread = running_thread ();
@@ -92,8 +105,16 @@ thread_init (void)
 void
 thread_start (void) 
 {
-  thread_create ("idle", PRI_MAX, idle, NULL);
+  /* Create the idle thread. */
+  struct semaphore idle_started;
+  sema_init (&idle_started, 0);
+  thread_create ("idle", PRI_MIN, idle, &idle_started);
+
+  /* Start preemptive thread scheduling. */
   intr_enable ();
+
+  /* Wait for the idle thread to initialize idle_thread. */
+  sema_down (&idle_started);
 }
 
 /* Called by the timer interrupt handler at each timer tick.
@@ -150,6 +171,7 @@ thread_create (const char *name, int priority,
   struct switch_entry_frame *ef;
   struct switch_threads_frame *sf;
   tid_t tid;
+  enum intr_level old_level;
 
   ASSERT (function != NULL);
 
@@ -162,6 +184,11 @@ thread_create (const char *name, int priority,
   init_thread (t, name, priority);
   tid = t->tid = allocate_tid ();
 
+  /* Prepare thread for first run by initializing its stack.
+     Do this atomically so intermediate values for the 'stack' 
+     member cannot be observed. */
+  old_level = intr_disable ();
+
   /* Stack frame for kernel_thread(). */
   kf = alloc_frame (t, sizeof *kf);
   kf->eip = NULL;
@@ -175,6 +202,9 @@ thread_create (const char *name, int priority,
   /* Stack frame for switch_threads(). */
   sf = alloc_frame (t, sizeof *sf);
   sf->eip = switch_entry;
+  sf->ebp = 0;
+
+  intr_set_level (old_level);
 
   /* Add to run queue. */
   thread_unblock (t);
@@ -200,7 +230,12 @@ thread_block (void)
 
 /* Transitions a blocked thread T to the ready-to-run state.
    This is an error if T is not blocked.  (Use thread_yield() to
-   make the running thread ready.) */
+   make the running thread ready.)
+
+   This function does not preempt the running thread.  This can
+   be important: if the caller had disabled interrupts itself,
+   it may expect that it can atomically unblock a thread and
+   update other data. */
 void
 thread_unblock (struct thread *t) 
 {
@@ -259,9 +294,11 @@ thread_exit (void)
   process_exit ();
 #endif
 
-  /* Just set our status to dying and schedule another process.
-     We will be destroyed during the call to schedule_tail(). */
+  /* Remove thread from all threads list, set our status to dying,
+     and schedule another process.  That process will destroy us
+     when it calls thread_schedule_tail(). */
   intr_disable ();
+  list_remove (&thread_current()->allelem);
   thread_current ()->status = THREAD_DYING;
   schedule ();
   NOT_REACHED ();
@@ -278,12 +315,30 @@ thread_yield (void)
   ASSERT (!intr_context ());
 
   old_level = intr_disable ();
-  list_push_back (&ready_list, &cur->elem);
+  if (cur != idle_thread) 
+    list_push_back (&ready_list, &cur->elem);
   cur->status = THREAD_READY;
   schedule ();
   intr_set_level (old_level);
 }
 
+/* Invoke function 'func' on all threads, passing along 'aux'.
+   This function must be called with interrupts off. */
+void
+thread_foreach (thread_action_func *func, void *aux)
+{
+  struct list_elem *e;
+
+  ASSERT (intr_get_level () == INTR_OFF);
+
+  for (e = list_begin (&all_list); e != list_end (&all_list);
+       e = list_next (e))
+    {
+      struct thread *t = list_entry (e, struct thread, allelem);
+      func (t, aux);
+    }
+}
+
 /* Sets the current thread's priority to NEW_PRIORITY. */
 void
 thread_set_priority (int new_priority) 
@@ -333,21 +388,17 @@ thread_get_recent_cpu (void)
 
    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. */
+   point it initializes idle_thread, "up"s the semaphore passed
+   to it to enable thread_start() to continue, 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) 
+idle (void *idle_started_ 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. */
+  struct semaphore *idle_started = idle_started_;
   idle_thread = thread_current ();
+  sema_up (idle_started);
 
   for (;;) 
     {
@@ -365,8 +416,9 @@ idle (void *aux UNUSED)
          one to occur, wasting as much as one clock tick worth of
          time.
 
-         See [IA32-v2a] "HLT", [IA32-v2b] "STI", and [IA32-v3] 7.7. */
-      asm ("sti; hlt");
+         See [IA32-v2a] "HLT", [IA32-v2b] "STI", and [IA32-v3a]
+         7.11.1 "HLT Instruction". */
+      asm volatile ("sti; hlt" : : : "memory");
     }
 }
 
@@ -407,6 +459,8 @@ is_thread (struct thread *t)
 static void
 init_thread (struct thread *t, const char *name, int priority)
 {
+  enum intr_level old_level;
+
   ASSERT (t != NULL);
   ASSERT (PRI_MIN <= priority && priority <= PRI_MAX);
   ASSERT (name != NULL);
@@ -417,6 +471,10 @@ init_thread (struct thread *t, const char *name, int priority)
   t->stack = (uint8_t *) t + PGSIZE;
   t->priority = priority;
   t->magic = THREAD_MAGIC;
+
+  old_level = intr_disable ();
+  list_push_back (&all_list, &t->allelem);
+  intr_set_level (old_level);
 }
 
 /* Allocates a SIZE-byte frame at the top of thread T's stack and
@@ -463,7 +521,7 @@ next_thread_to_run (void)
    After this function and its caller returns, the thread switch
    is complete. */
 void
-schedule_tail (struct thread *prev) 
+thread_schedule_tail (struct thread *prev)
 {
   struct thread *cur = running_thread ();
   
@@ -482,12 +540,13 @@ schedule_tail (struct thread *prev)
 
   /* If the thread we switched from is dying, destroy its struct
      thread.  This must happen late so that thread_exit() doesn't
-     pull out the rug under itself. */
-  if (prev != NULL && prev->status == THREAD_DYING) 
+     pull out the rug under itself.  (We don't free
+     initial_thread because its memory was not obtained via
+     palloc().) */
+  if (prev != NULL && prev->status == THREAD_DYING && prev != initial_thread) 
     {
       ASSERT (prev != cur);
-      if (prev != initial_thread)
-        palloc_free_page (prev);
+      palloc_free_page (prev);
     }
 }
 
@@ -496,8 +555,8 @@ schedule_tail (struct thread *prev)
    running to some other state.  This function finds another
    thread to run and switches to it.
 
-   It's not safe to call printf() until schedule_tail() has
-   completed. */
+   It's not safe to call printf() until thread_schedule_tail()
+   has completed. */
 static void
 schedule (void) 
 {
@@ -511,7 +570,7 @@ schedule (void)
 
   if (cur != next)
     prev = switch_threads (cur, next);
-  schedule_tail (prev); 
+  thread_schedule_tail (prev);
 }
 
 /* Returns a tid to use for a new thread. */