thread: Properly protect 'all_list' around insertion.

[pintos-anon] / src / threads / thread.c

diff --git a/src/threads/thread.c b/src/threads/thread.c
index b0d5a9138eb6e5a438fda9eabb3ec8e67d1ca519..d68c123fb2476420d09557f4f52d4a6fb12949f4 100644 (file)
--- 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/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/palloc.h"
 #include "threads/switch.h"
 #include "threads/synch.h"

+#include "threads/vaddr.h"

 #ifdef USERPROG
 #include "userprog/process.h"
 #endif
 #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;
 
    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;
 
 /* Idle thread. */
 static struct thread *idle_thread;
 


@@ -46,16 +50,25 @@ 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. */
 
 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. */
+
+/* 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);
 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 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);
 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
 static tid_t allocate_tid (void);
 
 /* Initializes the threading system by transforming the code


@@ -67,14 +80,18 @@ static tid_t allocate_tid (void);
 
    After calling this function, be sure to initialize the page
    allocator before trying to create any threads with
 
    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) 
 {
   ASSERT (intr_get_level () == INTR_OFF);
 
 void
 thread_init (void) 
 {
   ASSERT (intr_get_level () == INTR_OFF);
 

-  lock_init (&tid_lock, "tid");
+  lock_init (&tid_lock);

   list_init (&ready_list);
   list_init (&ready_list);

+  list_init (&all_list);

 
   /* Set up a thread structure for the running thread. */
   initial_thread = running_thread ();
 
   /* Set up a thread structure for the running thread. */
   initial_thread = running_thread ();


@@ -88,16 +105,26 @@ thread_init (void)
 void
 thread_start (void) 
 {
 void
 thread_start (void) 
 {

-  thread_create ("idle", PRI_DEFAULT, 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 ();
   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 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 ();
 void
 thread_tick (void) 
 {
   struct thread *t = thread_current ();

+
+  /* Update statistics. */

   if (t == idle_thread)
     idle_ticks++;
 #ifdef USERPROG
   if (t == idle_thread)
     idle_ticks++;
 #ifdef USERPROG


@@ -106,6 +133,10 @@ thread_tick (void)
 #endif
   else
     kernel_ticks++;
 #endif
   else
     kernel_ticks++;

+
+  /* Enforce preemption. */
+  if (++thread_ticks >= TIME_SLICE)
+    intr_yield_on_return ();

 }
 
 /* Prints thread statistics. */
 }
 
 /* Prints thread statistics. */


@@ -118,13 +149,15 @@ thread_print_stats (void)
 
 /* Creates a new kernel thread named NAME with the given initial
    PRIORITY, which executes FUNCTION passing AUX as the argument,
 
 /* Creates a new kernel thread named NAME with the given initial
    PRIORITY, 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.  It could even exit before
-   thread_create() returns.  Use a semaphore or some other form
-   of synchronization if you need to ensure ordering.  Returns
-   the thread identifier for the new thread, or TID_ERROR if
-   creation fails.
+   and adds it to the ready queue.  Returns the thread identifier
+   for the new thread, or TID_ERROR if creation fails.
+
+   If thread_start() has been called, then the new thread may be
+   scheduled before thread_create() returns.  It could even exit
+   before thread_create() returns.  Contrariwise, the original
+   thread may run for any amount of time before the new thread is
+   scheduled.  Use a semaphore or some other form of
+   synchronization if you need to ensure ordering.

 
    The code provided sets the new thread's `priority' member to
    PRIORITY, but no actual priority scheduling is implemented.
 
    The code provided sets the new thread's `priority' member to
    PRIORITY, but no actual priority scheduling is implemented.


@@ -138,6 +171,7 @@ thread_create (const char *name, int priority,
   struct switch_entry_frame *ef;
   struct switch_threads_frame *sf;
   tid_t tid;
   struct switch_entry_frame *ef;
   struct switch_threads_frame *sf;
   tid_t tid;

+  enum intr_level old_level;

 
   ASSERT (function != NULL);
 
 
   ASSERT (function != NULL);
 


@@ -150,6 +184,11 @@ thread_create (const char *name, int priority,
   init_thread (t, name, priority);
   tid = t->tid = allocate_tid ();
 
   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;
   /* Stack frame for kernel_thread(). */
   kf = alloc_frame (t, sizeof *kf);
   kf->eip = NULL;


@@ -163,6 +202,9 @@ thread_create (const char *name, int priority,
   /* Stack frame for switch_threads(). */
   sf = alloc_frame (t, sizeof *sf);
   sf->eip = switch_entry;
   /* 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);
 
   /* Add to run queue. */
   thread_unblock (t);


@@ -188,7 +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
 
 /* 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) 
 {
 void
 thread_unblock (struct thread *t) 
 {


@@ -247,9 +294,11 @@ thread_exit (void)
   process_exit ();
 #endif
 
   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 ();
   intr_disable ();

+  list_remove (&thread_current()->allelem);

   thread_current ()->status = THREAD_DYING;
   schedule ();
   NOT_REACHED ();
   thread_current ()->status = THREAD_DYING;
   schedule ();
   NOT_REACHED ();


@@ -266,27 +315,110 @@ thread_yield (void)
   ASSERT (!intr_context ());
 
   old_level = intr_disable ();
   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);
 }
   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) 
+{
+  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;
+}

 \f
 \f

-/* 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, "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
 static void

-idle (void *aux UNUSED) 
+idle (void *idle_started_ UNUSED) 

 {
 {

+  struct semaphore *idle_started = idle_started_;

   idle_thread = thread_current ();
   idle_thread = thread_current ();

+  sema_up (idle_started);

 
   for (;;) 
     {
       /* Let someone else run. */
       intr_disable ();
       thread_block ();
 
   for (;;) 
     {
       /* Let someone else run. */
       intr_disable ();
       thread_block ();

-      intr_enable ();

 
 

-      /* Use CPU `hlt' instruction to wait for interrupt. */
-      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 volatile ("sti; hlt" : : : "memory");

     }
 }
 
     }
 }
 


@@ -311,13 +443,13 @@ 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. */
      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));
+  asm ("mov %%esp, %0" : "=g" (esp));

   return pg_round_down (esp);
 }
 
 /* Returns true if T appears to point to a valid thread. */
 static bool
   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;
 }
 {
   return t != NULL && t->magic == THREAD_MAGIC;
 }


@@ -327,6 +459,8 @@ is_thread (struct thread *t)
 static void
 init_thread (struct thread *t, const char *name, int priority)
 {
 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);
   ASSERT (t != NULL);
   ASSERT (PRI_MIN <= priority && priority <= PRI_MAX);
   ASSERT (name != NULL);


@@ -337,6 +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;
   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
 }
 
 /* Allocates a SIZE-byte frame at the top of thread T's stack and


@@ -376,10 +514,14 @@ next_thread_to_run (void)
    the first time a thread is scheduled it is called by
    switch_entry() (see switch.S).
 
    the first time a thread is scheduled it is called by
    switch_entry() (see switch.S).
 

+   It's not safe to call printf() until the thread switch is
+   complete.  In practice that means that printf()s should be
+   added at the end of the function.
+

    After this function and its caller returns, the thread switch
    is complete. */
 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 ();
   
 {
   struct thread *cur = running_thread ();
   


@@ -388,6 +530,9 @@ schedule_tail (struct thread *prev)
   /* Mark us as running. */
   cur->status = THREAD_RUNNING;
 
   /* Mark us as running. */
   cur->status = THREAD_RUNNING;
 

+  /* Start new time slice. */
+  thread_ticks = 0;
+

 #ifdef USERPROG
   /* Activate the new address space. */
   process_activate ();
 #ifdef USERPROG
   /* Activate the new address space. */
   process_activate ();


@@ -395,19 +540,23 @@ 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
 
   /* 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);
     {
       ASSERT (prev != cur);

-      if (prev != initial_thread)
-        palloc_free_page (prev);
+      palloc_free_page (prev);

     }
 }
 
 /* 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
     }
 }
 
 /* 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. */
+   thread to run and switches to it.
+
+   It's not safe to call printf() until thread_schedule_tail()
+   has completed. */

 static void
 schedule (void) 
 {
 static void
 schedule (void) 
 {


@@ -421,7 +570,7 @@ schedule (void)
 
   if (cur != next)
     prev = switch_threads (cur, next);
 
   if (cur != next)
     prev = switch_threads (cur, next);

-  schedule_tail (prev); 
+  thread_schedule_tail (prev);

 }
 
 /* Returns a tid to use for a new thread. */
 }
 
 /* Returns a tid to use for a new thread. */