X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=src%2Fthreads%2Fthread.c;h=fed6b841aded48864edee8307fec6fb6090c87ae;hb=c9c283cb3e26a5b6d918ee47dcf8efe28522b18d;hp=04b446f9f475d0225b45b4f6e6d797a12defbd87;hpb=987024569c1e5e9468238849dd79ec8d386352e6;p=pintos-anon

diff --git a/src/threads/thread.c b/src/threads/thread.c
index 04b446f..fed6b84 100644
--- a/src/threads/thread.c
+++ b/src/threads/thread.c
@@ -2,123 +2,167 @@
 #include <stddef.h>
 #include "debug.h"
 #include "interrupt.h"
+#include "intr-stubs.h"
 #include "lib.h"
+#include "gdt.h"
 #include "mmu.h"
 #include "palloc.h"
 #include "random.h"
 #include "switch.h"
 
-uint32_t thread_stack_ofs = offsetof (struct thread, stack);
+#define THREAD_MAGIC 0x1234abcdu
 
+/* List of processes in THREAD_READY state, that is, processes
+   that are ready to run but not actually running. */
 static struct list run_queue;
 
-void
-thread_init (void) 
-{
-  list_init (&run_queue);
-}
+/* Idle thread. */
+static struct thread *idle_thread;      /* Thread. */
+static void idle (void *aux UNUSED);    /* Thread function. */
 
-struct thread_root_frame 
+/* Stack frame for kernel_thread(). */
+struct kernel_thread_frame 
   {
     void *eip;                  /* Return address. */
     void (*function) (void *);  /* Function to call. */
     void *aux;                  /* Auxiliary data for function. */
   };
 
-static void
-thread_root (void (*function) (void *aux), void *aux) 
-{
-  ASSERT (function != NULL);
-  
-  function (aux);
-  thread_exit ();
-}
+static void kernel_thread (void (*function) (void *aux), void *aux);
 
-static struct thread *
-new_thread (const char *name) 
+static struct thread *next_thread_to_run (void);
+static struct thread *new_thread (const char *name);
+static bool is_thread (struct thread *t);
+static void *alloc_frame (struct thread *t, size_t size);
+static void destroy_thread (struct thread *t);
+static void schedule (void);
+void schedule_tail (struct thread *prev);
+
+/* Initializes the threading system.  After calling, create some
+   threads with thread_create() or thread_execute(), then start
+   the scheduler with thread_start(). */
+void
+thread_init (void) 
 {
-  struct thread *t;
+  ASSERT (intr_get_level () == INTR_OFF);
 
-  ASSERT (name != NULL);
-  
-  t = palloc_get (PAL_ZERO);
-  if (t != NULL)
-    {
-      strlcpy (t->name, name, sizeof t->name);
-      t->stack = (uint8_t *) t + PGSIZE;
-      t->status = THREAD_BLOCKED;
-    }
-  
-  return t;
+  /* Initialize run queue. */
+  list_init (&run_queue);
+
+  /* Create idle thread. */
+  idle_thread = thread_create ("idle", idle, NULL);
+  idle_thread->status = THREAD_BLOCKED;
 }
 
-static void *
-alloc_frame (struct thread *t, size_t size) 
+/* Starts the thread scheduler.  The caller should have created
+   some threads with thread_create() or thread_execute().  Never
+   returns to the caller. */
+void
+thread_start (void) 
 {
-  ASSERT (size % sizeof (uint32_t) == 0);
+  struct thread *t = next_thread_to_run ();
+  if (t->status == THREAD_READY)
+    list_remove (&t->rq_elem);
+  t->status = THREAD_RUNNING;
+  switch_threads (NULL, t);
 
-  t->stack -= size;
-  return t->stack;
+  NOT_REACHED ();
 }
 
+/* Creates a new kernel thread named NAME, which executes
+   FUNCTION passing AUX as the argument, and adds it to the ready
+   queue.  If thread_start() has been called, then the new thread
+   may be scheduled before thread_create() returns.  Use a
+   semaphore or some other form of synchronization if you need to
+   ensure ordering. */
 struct thread *
 thread_create (const char *name, void (*function) (void *aux), void *aux) 
 {
   struct thread *t;
-  struct thread_root_frame *rf;
-  struct switch_thunk_frame *tf;
-  struct switch_frame *sf;
+  struct kernel_thread_frame *kf;
+  struct switch_entry_frame *ef;
+  struct switch_threads_frame *sf;
 
   ASSERT (function != NULL);
 
   t = new_thread (name);
 
-  /* Stack frame for thread_root(). */
-  rf = alloc_frame (t, sizeof *rf);
-  rf->eip = NULL;
-  rf->function = function;
-  rf->aux = aux;
+  /* Stack frame for kernel_thread(). */
+  kf = alloc_frame (t, sizeof *kf);
+  kf->eip = NULL;
+  kf->function = function;
+  kf->aux = aux;
 
-  /* Stack frame for switch_thunk(). */
-  tf = alloc_frame (t, sizeof *tf);
-  tf->eip = (void (*) (void)) thread_root;
+  /* Stack frame for switch_entry(). */
+  ef = alloc_frame (t, sizeof *ef);
+  ef->eip = (void (*) (void)) kernel_thread;
 
-  /* Stack frame for thread_switch(). */
+  /* Stack frame for switch_threads(). */
   sf = alloc_frame (t, sizeof *sf);
-  sf->eip = (void (*) (void)) switch_thunk;
+  sf->eip = switch_entry;
 
   /* Add to run queue. */
-  thread_ready (t);
+  thread_wake (t);
 
   return t;
 }
 
-struct thread *
-thread_current (void) 
-{
-  uint32_t *esp;
-  asm ("movl %%esp, %0\n" : "=g" (esp));
-  return pg_round_down (esp);
-}
-
 #ifdef USERPROG
+/* Starts a new thread running a user program loaded from
+   FILENAME, and adds it to the ready queue.  If thread_start()
+   has been called, then new thread may be scheduled before
+   thread_execute() returns.*/
 bool
 thread_execute (const char *filename) 
 {
-  struct thread *t = new_thread (filename);
+  struct thread *t;
+  struct intr_frame *if_;
+  struct switch_entry_frame *ef;
+  struct switch_threads_frame *sf;
+  void (*start) (void);
+
+  ASSERT (filename != NULL);
+
+  t = new_thread (filename);
   if (t == NULL)
     return false;
   
-  if (!addrspace_load (&t->addrspace, filename)) 
-    panic ("%s: program load failed", filename);
-  printk ("%s: loaded\n", filename);
+  if (!addrspace_load (t, filename, &start)) 
+    PANIC ("%s: program load failed", filename);
+
+  /* Interrupt frame. */
+  if_ = alloc_frame (t, sizeof *if_);
+  if_->es = SEL_UDSEG;
+  if_->ds = SEL_UDSEG;
+  if_->eip = start;
+  if_->cs = SEL_UCSEG;
+  if_->eflags = FLAG_IF | FLAG_MBS;
+  if_->esp = PHYS_BASE;
+  if_->ss = SEL_UDSEG;
+
+  /* Stack frame for switch_entry(). */
+  ef = alloc_frame (t, sizeof *ef);
+  ef->eip = intr_exit;
+
+  /* Stack frame for switch_threads(). */
+  sf = alloc_frame (t, sizeof *sf);
+  sf->eip = switch_entry;
+
+  /* Add to run queue. */
+  thread_wake (t);
+
   return true;
 }
 #endif
 
+/* Transitions T from its current state to THREAD_READY, the
+   ready-to-run state.  On entry, T must be ready or blocked.
+   (Use thread_yield() to make the running thread ready.) */
 void
-thread_ready (struct thread *t) 
+thread_wake (struct thread *t) 
 {
+  ASSERT (is_thread (t));
+  ASSERT (t->status == THREAD_READY || t->status == THREAD_BLOCKED);
   if (t->status != THREAD_READY) 
     {
       list_push_back (&run_queue, &t->rq_elem);
@@ -126,133 +170,226 @@ thread_ready (struct thread *t)
     }
 }
 
-static struct thread *
-find_next_to_run (void) 
+/* Returns the name of thread T. */
+const char *
+thread_name (struct thread *t) 
 {
-  if (list_empty (&run_queue))
-    return NULL;
-  else
-    return list_entry (list_pop_front (&run_queue), struct thread, rq_elem);
+  ASSERT (is_thread (t));
+  return t->name;
 }
 
-static void
-idle (void) 
+/* Returns the running thread. */
+struct thread *
+thread_current (void) 
 {
-  static int idle = 0;
-  if (idle++ == 0)
-    printk ("idle\n");
+  uint32_t *esp;
+  struct thread *t;
+
+  /* Copy the CPU's stack pointer into `esp', and then round that
+     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 ("movl %%esp, %0\n" : "=g" (esp));
+  t = pg_round_down (esp);
+
+  /* Make sure T is really a thread.
+     If this assertion fires, then your thread may have
+     overflowed its stack.  Each thread has less than 4 kB of
+     stack, so a few big automatic arrays or moderate recursion
+     can cause stack overflow. */
+  ASSERT (is_thread (t));
+
+  return t;
 }
 
+/* Deschedules the current thread and destroys it.  Never
+   returns to the caller. */
 void
-thread_destroy (struct thread *t) 
+thread_exit (void) 
 {
-  ASSERT (t->status == THREAD_DYING);
-  ASSERT (t != thread_current ());
+  ASSERT (!intr_context ());
 
-  palloc_free (t);
+  intr_disable ();
+  thread_current ()->status = THREAD_DYING;
+  schedule ();
+  NOT_REACHED ();
 }
 
+/* Yields the CPU.  The current thread is not put to sleep and
+   may be scheduled again immediately at the scheduler's whim. */
 void
-thread_schedule (void) 
+thread_yield (void) 
 {
-  struct thread *cur, *next, *prev;
-
-  ASSERT (intr_get_level () == IF_OFF);
+  struct thread *cur = thread_current ();
+  enum intr_level old_level;
+  
+  ASSERT (!intr_context ());
 
-  cur = thread_current ();
-  ASSERT (cur->status != THREAD_RUNNING);
+  old_level = intr_disable ();
+  list_push_back (&run_queue, &cur->rq_elem);
+  cur->status = THREAD_READY;
+  schedule ();
+  intr_set_level (old_level);
+}
 
-  while ((next = find_next_to_run ()) == NULL)
-    idle ();
+/* Puts the current thread to sleep.  It will not be scheduled
+   again until awoken by thread_wake(). */
+void
+thread_sleep (void) 
+{
+  ASSERT (!intr_context ());
+  ASSERT (intr_get_level () == INTR_OFF);
 
-  next->status = THREAD_RUNNING;
-  prev = switch_threads (cur, next);
+  thread_current ()->status = THREAD_BLOCKED;
+  schedule ();
+}
+
+/* Idle thread.  Executes when no other thread is ready to run. */
+static void
+idle (void *aux UNUSED) 
+{
+  for (;;) 
+    {
+      /* Wait for an interrupt. */
+      DEBUG (idle, "idle");
+      asm ("hlt");
+
+      /* Let someone else run. */
+      intr_disable ();
+      thread_sleep ();
+      intr_enable ();
+    }
+}
 
-  /* Prevent GCC from reordering anything around the thread
-     switch. */
-  asm volatile ("" : : : "memory");
+/* Function used as the basis for a kernel thread. */
+static void
+kernel_thread (void (*function) (void *aux), void *aux) 
+{
+  ASSERT (function != NULL);
 
-#ifdef USERPROG
-  addrspace_activate (&cur->addrspace);
-#endif
+  intr_enable ();       /* The scheduler runs with interrupts off. */
+  function (aux);       /* Execute the thread function. */
+  thread_exit ();       /* If function() returns, kill the thread. */
+}
+
+/* Returns true if T appears to point to a valid thread. */
+static bool
+is_thread (struct thread *t) 
+{
+  return t != NULL && t->magic == THREAD_MAGIC;
+}
 
-  if (prev != NULL && prev->status == THREAD_DYING) 
-    thread_destroy (prev);
+/* Creates a new thread named NAME and initializes its fields.
+   Returns the new thread if successful or a null pointer on
+   failure. */
+static struct thread *
+new_thread (const char *name) 
+{
+  struct thread *t;
 
-  intr_enable ();
+  ASSERT (name != NULL);
+  
+  t = palloc_get (PAL_ZERO);
+  if (t != NULL)
+    {
+      strlcpy (t->name, name, sizeof t->name);
+      t->stack = (uint8_t *) t + PGSIZE;
+      t->status = THREAD_BLOCKED;
+      t->magic = THREAD_MAGIC;
+    }
+  
+  return t;
 }
 
-void
-thread_yield (void) 
+/* Allocates a SIZE-byte frame at the top of thread T's stack and
+   returns a pointer to the frame's base. */
+static void *
+alloc_frame (struct thread *t, size_t size) 
 {
-  ASSERT (!intr_context ());
+  /* Stack data is always allocated in word-size units. */
+  ASSERT (is_thread (t));
+  ASSERT (size % sizeof (uint32_t) == 0);
 
-  intr_disable ();
-  thread_ready (thread_current ());
-  thread_schedule ();
+  t->stack -= size;
+  return t->stack;
 }
 
-void
-thread_start (struct thread *t) 
+/* Chooses and returns the next thread to be scheduled.  Should
+   return a thread from the run queue, unless the run queue is
+   empty.  (If the running thread can continue running, then it
+   will be in the run queue.)  If the run queue is empty, return
+   idle_thread. */
+static struct thread *
+next_thread_to_run (void) 
 {
-  ASSERT (intr_get_level () == IF_OFF);
-
-  if (t->status == THREAD_READY) 
-    list_remove (&t->rq_elem);
-  t->status = THREAD_RUNNING;
-  switch_threads (NULL, t);
+  if (list_empty (&run_queue))
+    return idle_thread;
+  else
+    return list_entry (list_pop_front (&run_queue), struct thread, rq_elem);
 }
 
-void
-thread_exit (void) 
+/* Destroys T, which must be in the dying state and must not be
+   the running thread. */
+static void
+destroy_thread (struct thread *t) 
 {
-  ASSERT (!intr_context ());
+  ASSERT (is_thread (t));
+  ASSERT (t->status == THREAD_DYING);
+  ASSERT (t != thread_current ());
 
-  intr_disable ();
-  thread_current ()->status = THREAD_DYING;
-  thread_schedule ();
+  addrspace_destroy (t);
+  palloc_free (t);
 }
 
+/* Completes a thread switch by activating the new thread's page
+   tables, and, if the previous thread is dying, destroying it.
+
+   At this function's invocation, we just switched from thread
+   PREV, the new thread is already running, and interrupts are
+   still disabled.  This function is normally invoked by
+   thread_schedule() as its final action before returning, but
+   the first time a thread is scheduled it is called by
+   switch_entry() (see switch.S).
+
+   After this function and its caller returns, the thread switch
+   is complete. */
 void
-thread_sleep (void) 
+schedule_tail (struct thread *prev) 
 {
-  ASSERT (!intr_context ());
-  ASSERT (intr_get_level () == IF_OFF);
+  struct thread *cur = thread_current ();
+  
+  ASSERT (intr_get_level () == INTR_OFF);
 
-  thread_current ()->status = THREAD_BLOCKED;
-  thread_schedule ();
+  cur->status = THREAD_RUNNING;
+  if (prev != NULL && prev->status == THREAD_DYING) 
+    destroy_thread (prev);
+
+#ifdef USERPROG
+  addrspace_activate (cur);
+#endif
 }
 
+/* Schedules a new process.  At entry, interrupts must be off and
+   the running process's state must have been changed from
+   running to some other state.  This function finds another
+   thread to run and switches to it. */
 static void
-tfunc (void *aux UNUSED) 
+schedule (void) 
 {
-  for (;;) 
-    {
-      size_t count, i;
-      if (random_ulong () % 5 == 0)
-        {
-          printk ("%s exiting\n", thread_current ()->name);
-          break;
-        }
-      count = random_ulong () % 25 * 10000;
-      printk ("%s waiting %zu: ", thread_current ()->name, count);
-      for (i = 0; i < count; i++);
-      printk ("%s\n", thread_current ()->name);
-    }
-}
+  struct thread *cur = thread_current ();
+  struct thread *next = next_thread_to_run ();
 
-void
-thread_self_test (void)
-{
-  struct thread *t;
-  int i;
-    
-  for (i = 0; i < 4; i++) 
+  ASSERT (intr_get_level () == INTR_OFF);
+  ASSERT (cur->status != THREAD_RUNNING);
+  ASSERT (is_thread (next));
+
+  if (cur != next)
     {
-      char name[2];
-      name[0] = 'a' + i;
-      name[1] = 0;
-      t = thread_create (name, tfunc, NULL); 
+      struct thread *prev = switch_threads (cur, next);
+      schedule_tail (prev); 
     }
-  thread_start (t); 
 }
+
+/* Offset of `stack' member within `struct thread'.
+   Used by switch.S, which can't figure it out on its own. */
+uint32_t thread_stack_ofs = offsetof (struct thread, stack);