1 #include "threads/thread.h"
7 #include "threads/flags.h"
8 #include "threads/interrupt.h"
9 #include "threads/intr-stubs.h"
10 #include "threads/mmu.h"
11 #include "threads/palloc.h"
12 #include "threads/switch.h"
13 #include "threads/synch.h"
15 #include "userprog/process.h"
18 /* Random value for struct thread's `magic' member.
19 Used to detect stack overflow. See the big comment at the top
20 of thread.h for details. */
21 #define THREAD_MAGIC 0xcd6abf4b
23 /* List of processes in THREAD_READY state, that is, processes
24 that are ready to run but not actually running. */
25 static struct list ready_list;
28 static struct thread *idle_thread;
30 /* Initial thread, the thread running init.c:main(). */
31 static struct thread *initial_thread;
33 /* Lock used by allocate_tid(). */
34 static struct lock tid_lock;
36 /* Stack frame for kernel_thread(). */
37 struct kernel_thread_frame
39 void *eip; /* Return address. */
40 thread_func *function; /* Function to call. */
41 void *aux; /* Auxiliary data for function. */
45 static long long idle_ticks; /* # of timer ticks spent idle. */
46 static long long kernel_ticks; /* # of timer ticks in kernel threads. */
47 static long long user_ticks; /* # of timer ticks in user programs. */
50 #define TIME_SLICE 4 /* # of timer ticks to give each thread. */
51 static unsigned thread_ticks; /* # of timer ticks since last yield. */
53 static void kernel_thread (thread_func *, void *aux);
55 static void idle (void *aux UNUSED);
56 static struct thread *running_thread (void);
57 static struct thread *next_thread_to_run (void);
58 static void init_thread (struct thread *, const char *name, int priority);
59 static bool is_thread (struct thread *) UNUSED;
60 static void *alloc_frame (struct thread *, size_t size);
61 static void schedule (void);
62 void schedule_tail (struct thread *prev);
63 static tid_t allocate_tid (void);
65 /* Initializes the threading system by transforming the code
66 that's currently running into a thread. This can't work in
67 general and it is possible in this case only because loader.S
68 was careful to put the bottom of the stack at a page boundary.
70 Also initializes the run queue and the tid lock.
72 After calling this function, be sure to initialize the page
73 allocator before trying to create any threads with
78 ASSERT (intr_get_level () == INTR_OFF);
80 lock_init (&tid_lock);
81 list_init (&ready_list);
83 /* Set up a thread structure for the running thread. */
84 initial_thread = running_thread ();
85 init_thread (initial_thread, "main", PRI_DEFAULT);
86 initial_thread->status = THREAD_RUNNING;
87 initial_thread->tid = allocate_tid ();
90 /* Starts preemptive thread scheduling by enabling interrupts.
91 Also creates the idle thread. */
95 thread_create ("idle", PRI_MAX, idle, NULL);
99 /* Called by the timer interrupt handler at each timer tick. */
103 struct thread *t = thread_current ();
105 /* Update statistics. */
106 if (t == idle_thread)
109 else if (t->pagedir != NULL)
115 /* Enforce preemption. */
116 if (++thread_ticks >= TIME_SLICE)
117 intr_yield_on_return ();
120 /* Prints thread statistics. */
122 thread_print_stats (void)
124 printf ("Thread: %lld idle ticks, %lld kernel ticks, %lld user ticks\n",
125 idle_ticks, kernel_ticks, user_ticks);
128 /* Creates a new kernel thread named NAME with the given initial
129 PRIORITY, which executes FUNCTION passing AUX as the argument,
130 and adds it to the ready queue. Returns the thread identifier
131 for the new thread, or TID_ERROR if creation fails.
133 If thread_start() has been called, then the new thread may be
134 scheduled before thread_create() returns. It could even exit
135 before thread_create() returns. Contrariwise, the original
136 thread may run for any amount of time before the new thread is
137 scheduled. Use a semaphore or some other form of
138 synchronization if you need to ensure ordering.
140 The code provided sets the new thread's `priority' member to
141 PRIORITY, but no actual priority scheduling is implemented.
142 Priority scheduling is the goal of Problem 1-3. */
144 thread_create (const char *name, int priority,
145 thread_func *function, void *aux)
148 struct kernel_thread_frame *kf;
149 struct switch_entry_frame *ef;
150 struct switch_threads_frame *sf;
153 ASSERT (function != NULL);
155 /* Allocate thread. */
156 t = palloc_get_page (PAL_ZERO);
160 /* Initialize thread. */
161 init_thread (t, name, priority);
162 tid = t->tid = allocate_tid ();
164 /* Stack frame for kernel_thread(). */
165 kf = alloc_frame (t, sizeof *kf);
167 kf->function = function;
170 /* Stack frame for switch_entry(). */
171 ef = alloc_frame (t, sizeof *ef);
172 ef->eip = (void (*) (void)) kernel_thread;
174 /* Stack frame for switch_threads(). */
175 sf = alloc_frame (t, sizeof *sf);
176 sf->eip = switch_entry;
178 /* Add to run queue. */
184 /* Puts the current thread to sleep. It will not be scheduled
185 again until awoken by thread_unblock().
187 This function must be called with interrupts turned off. It
188 is usually a better idea to use one of the synchronization
189 primitives in synch.h. */
193 ASSERT (!intr_context ());
194 ASSERT (intr_get_level () == INTR_OFF);
196 thread_current ()->status = THREAD_BLOCKED;
200 /* Transitions a blocked thread T to the ready-to-run state.
201 This is an error if T is not blocked. (Use thread_yield() to
202 make the running thread ready.) */
204 thread_unblock (struct thread *t)
206 enum intr_level old_level;
208 ASSERT (is_thread (t));
210 old_level = intr_disable ();
211 ASSERT (t->status == THREAD_BLOCKED);
212 list_push_back (&ready_list, &t->elem);
213 t->status = THREAD_READY;
214 intr_set_level (old_level);
217 /* Returns the name of the running thread. */
221 return thread_current ()->name;
224 /* Returns the running thread.
225 This is running_thread() plus a couple of sanity checks.
226 See the big comment at the top of thread.h for details. */
228 thread_current (void)
230 struct thread *t = running_thread ();
232 /* Make sure T is really a thread.
233 If either of these assertions fire, then your thread may
234 have overflowed its stack. Each thread has less than 4 kB
235 of stack, so a few big automatic arrays or moderate
236 recursion can cause stack overflow. */
237 ASSERT (is_thread (t));
238 ASSERT (t->status == THREAD_RUNNING);
243 /* Returns the running thread's tid. */
247 return thread_current ()->tid;
250 /* Deschedules the current thread and destroys it. Never
251 returns to the caller. */
255 ASSERT (!intr_context ());
261 /* Just set our status to dying and schedule another process.
262 We will be destroyed during the call to schedule_tail(). */
264 thread_current ()->status = THREAD_DYING;
269 /* Yields the CPU. The current thread is not put to sleep and
270 may be scheduled again immediately at the scheduler's whim. */
274 struct thread *cur = thread_current ();
275 enum intr_level old_level;
277 ASSERT (!intr_context ());
279 old_level = intr_disable ();
280 list_push_back (&ready_list, &cur->elem);
281 cur->status = THREAD_READY;
283 intr_set_level (old_level);
286 /* Sets the current thread's priority to NEW_PRIORITY. */
288 thread_set_priority (int new_priority)
290 thread_current ()->priority = new_priority;
293 /* Returns the current thread's priority. */
295 thread_get_priority (void)
297 return thread_current ()->priority;
300 /* Sets the current thread's nice value to NICE. */
302 thread_set_nice (int nice UNUSED)
304 /* Not yet implemented. */
307 /* Returns the current thread's nice value. */
309 thread_get_nice (void)
311 /* Not yet implemented. */
315 /* Returns 100 times the system load average. */
317 thread_get_load_avg (void)
319 /* Not yet implemented. */
323 /* Returns 100 times the current thread's recent_cpu value. */
325 thread_get_recent_cpu (void)
327 /* Not yet implemented. */
331 /* Idle thread. Executes when no other thread is ready to run. */
333 idle (void *aux UNUSED)
335 idle_thread = thread_current ();
339 /* Let someone else run. */
343 /* Re-enable interrupts and wait for the next one.
345 The `sti' instruction disables interrupts until the
346 completion of the next instruction, so these two
347 instructions are executed atomically. This atomicity is
348 important; otherwise, an interrupt could be handled
349 between re-enabling interrupts and waiting for the next
350 one to occur, wasting as much as one clock tick worth of
353 See [IA32-v2a] "HLT", [IA32-v2b] "STI", and [IA32-v3] 7.7. */
358 /* Function used as the basis for a kernel thread. */
360 kernel_thread (thread_func *function, void *aux)
362 ASSERT (function != NULL);
364 intr_enable (); /* The scheduler runs with interrupts off. */
365 function (aux); /* Execute the thread function. */
366 thread_exit (); /* If function() returns, kill the thread. */
369 /* Returns the running thread. */
371 running_thread (void)
375 /* Copy the CPU's stack pointer into `esp', and then round that
376 down to the start of a page. Because `struct thread' is
377 always at the beginning of a page and the stack pointer is
378 somewhere in the middle, this locates the curent thread. */
379 asm ("mov %0, %%esp" : "=g" (esp));
380 return pg_round_down (esp);
383 /* Returns true if T appears to point to a valid thread. */
385 is_thread (struct thread *t)
387 return t != NULL && t->magic == THREAD_MAGIC;
390 /* Does basic initialization of T as a blocked thread named
393 init_thread (struct thread *t, const char *name, int priority)
396 ASSERT (PRI_MIN <= priority && priority <= PRI_MAX);
397 ASSERT (name != NULL);
399 memset (t, 0, sizeof *t);
400 t->status = THREAD_BLOCKED;
401 strlcpy (t->name, name, sizeof t->name);
402 t->stack = (uint8_t *) t + PGSIZE;
403 t->priority = priority;
404 t->magic = THREAD_MAGIC;
407 /* Allocates a SIZE-byte frame at the top of thread T's stack and
408 returns a pointer to the frame's base. */
410 alloc_frame (struct thread *t, size_t size)
412 /* Stack data is always allocated in word-size units. */
413 ASSERT (is_thread (t));
414 ASSERT (size % sizeof (uint32_t) == 0);
420 /* Chooses and returns the next thread to be scheduled. Should
421 return a thread from the run queue, unless the run queue is
422 empty. (If the running thread can continue running, then it
423 will be in the run queue.) If the run queue is empty, return
425 static struct thread *
426 next_thread_to_run (void)
428 if (list_empty (&ready_list))
431 return list_entry (list_pop_front (&ready_list), struct thread, elem);
434 /* Completes a thread switch by activating the new thread's page
435 tables, and, if the previous thread is dying, destroying it.
437 At this function's invocation, we just switched from thread
438 PREV, the new thread is already running, and interrupts are
439 still disabled. This function is normally invoked by
440 thread_schedule() as its final action before returning, but
441 the first time a thread is scheduled it is called by
442 switch_entry() (see switch.S).
444 It's not safe to call printf() until the thread switch is
445 complete. In practice that means that printf()s should be
446 added at the end of the function.
448 After this function and its caller returns, the thread switch
451 schedule_tail (struct thread *prev)
453 struct thread *cur = running_thread ();
455 ASSERT (intr_get_level () == INTR_OFF);
457 /* Mark us as running. */
458 cur->status = THREAD_RUNNING;
460 /* Start new time slice. */
464 /* Activate the new address space. */
468 /* If the thread we switched from is dying, destroy its struct
469 thread. This must happen late so that thread_exit() doesn't
470 pull out the rug under itself. */
471 if (prev != NULL && prev->status == THREAD_DYING)
473 ASSERT (prev != cur);
474 if (prev != initial_thread)
475 palloc_free_page (prev);
479 /* Schedules a new process. At entry, interrupts must be off and
480 the running process's state must have been changed from
481 running to some other state. This function finds another
482 thread to run and switches to it.
484 It's not safe to call printf() until schedule_tail() has
489 struct thread *cur = running_thread ();
490 struct thread *next = next_thread_to_run ();
491 struct thread *prev = NULL;
493 ASSERT (intr_get_level () == INTR_OFF);
494 ASSERT (cur->status != THREAD_RUNNING);
495 ASSERT (is_thread (next));
498 prev = switch_threads (cur, next);
499 schedule_tail (prev);
502 /* Returns a tid to use for a new thread. */
506 static tid_t next_tid = 1;
509 lock_acquire (&tid_lock);
511 lock_release (&tid_lock);
516 /* Offset of `stack' member within `struct thread'.
517 Used by switch.S, which can't figure it out on its own. */
518 uint32_t thread_stack_ofs = offsetof (struct thread, stack);