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.
100 Thus, this function runs in an external interrupt context. */
104 struct thread *t = thread_current ();
106 /* Update statistics. */
107 if (t == idle_thread)
110 else if (t->pagedir != NULL)
116 /* Enforce preemption. */
117 if (++thread_ticks >= TIME_SLICE)
118 intr_yield_on_return ();
121 /* Prints thread statistics. */
123 thread_print_stats (void)
125 printf ("Thread: %lld idle ticks, %lld kernel ticks, %lld user ticks\n",
126 idle_ticks, kernel_ticks, user_ticks);
129 /* Creates a new kernel thread named NAME with the given initial
130 PRIORITY, which executes FUNCTION passing AUX as the argument,
131 and adds it to the ready queue. Returns the thread identifier
132 for the new thread, or TID_ERROR if creation fails.
134 If thread_start() has been called, then the new thread may be
135 scheduled before thread_create() returns. It could even exit
136 before thread_create() returns. Contrariwise, the original
137 thread may run for any amount of time before the new thread is
138 scheduled. Use a semaphore or some other form of
139 synchronization if you need to ensure ordering.
141 The code provided sets the new thread's `priority' member to
142 PRIORITY, but no actual priority scheduling is implemented.
143 Priority scheduling is the goal of Problem 1-3. */
145 thread_create (const char *name, int priority,
146 thread_func *function, void *aux)
149 struct kernel_thread_frame *kf;
150 struct switch_entry_frame *ef;
151 struct switch_threads_frame *sf;
154 ASSERT (function != NULL);
156 /* Allocate thread. */
157 t = palloc_get_page (PAL_ZERO);
161 /* Initialize thread. */
162 init_thread (t, name, priority);
163 tid = t->tid = allocate_tid ();
165 /* Stack frame for kernel_thread(). */
166 kf = alloc_frame (t, sizeof *kf);
168 kf->function = function;
171 /* Stack frame for switch_entry(). */
172 ef = alloc_frame (t, sizeof *ef);
173 ef->eip = (void (*) (void)) kernel_thread;
175 /* Stack frame for switch_threads(). */
176 sf = alloc_frame (t, sizeof *sf);
177 sf->eip = switch_entry;
179 /* Add to run queue. */
185 /* Puts the current thread to sleep. It will not be scheduled
186 again until awoken by thread_unblock().
188 This function must be called with interrupts turned off. It
189 is usually a better idea to use one of the synchronization
190 primitives in synch.h. */
194 ASSERT (!intr_context ());
195 ASSERT (intr_get_level () == INTR_OFF);
197 thread_current ()->status = THREAD_BLOCKED;
201 /* Transitions a blocked thread T to the ready-to-run state.
202 This is an error if T is not blocked. (Use thread_yield() to
203 make the running thread ready.) */
205 thread_unblock (struct thread *t)
207 enum intr_level old_level;
209 ASSERT (is_thread (t));
211 old_level = intr_disable ();
212 ASSERT (t->status == THREAD_BLOCKED);
213 list_push_back (&ready_list, &t->elem);
214 t->status = THREAD_READY;
215 intr_set_level (old_level);
218 /* Returns the name of the running thread. */
222 return thread_current ()->name;
225 /* Returns the running thread.
226 This is running_thread() plus a couple of sanity checks.
227 See the big comment at the top of thread.h for details. */
229 thread_current (void)
231 struct thread *t = running_thread ();
233 /* Make sure T is really a thread.
234 If either of these assertions fire, then your thread may
235 have overflowed its stack. Each thread has less than 4 kB
236 of stack, so a few big automatic arrays or moderate
237 recursion can cause stack overflow. */
238 ASSERT (is_thread (t));
239 ASSERT (t->status == THREAD_RUNNING);
244 /* Returns the running thread's tid. */
248 return thread_current ()->tid;
251 /* Deschedules the current thread and destroys it. Never
252 returns to the caller. */
256 ASSERT (!intr_context ());
262 /* Just set our status to dying and schedule another process.
263 We will be destroyed during the call to schedule_tail(). */
265 thread_current ()->status = THREAD_DYING;
270 /* Yields the CPU. The current thread is not put to sleep and
271 may be scheduled again immediately at the scheduler's whim. */
275 struct thread *cur = thread_current ();
276 enum intr_level old_level;
278 ASSERT (!intr_context ());
280 old_level = intr_disable ();
281 list_push_back (&ready_list, &cur->elem);
282 cur->status = THREAD_READY;
284 intr_set_level (old_level);
287 /* Sets the current thread's priority to NEW_PRIORITY. */
289 thread_set_priority (int new_priority)
291 thread_current ()->priority = new_priority;
294 /* Returns the current thread's priority. */
296 thread_get_priority (void)
298 return thread_current ()->priority;
301 /* Sets the current thread's nice value to NICE. */
303 thread_set_nice (int nice UNUSED)
305 /* Not yet implemented. */
308 /* Returns the current thread's nice value. */
310 thread_get_nice (void)
312 /* Not yet implemented. */
316 /* Returns 100 times the system load average. */
318 thread_get_load_avg (void)
320 /* Not yet implemented. */
324 /* Returns 100 times the current thread's recent_cpu value. */
326 thread_get_recent_cpu (void)
328 /* Not yet implemented. */
332 /* Idle thread. Executes when no other thread is ready to run. */
334 idle (void *aux UNUSED)
336 idle_thread = thread_current ();
340 /* Let someone else run. */
344 /* Re-enable interrupts and wait for the next one.
346 The `sti' instruction disables interrupts until the
347 completion of the next instruction, so these two
348 instructions are executed atomically. This atomicity is
349 important; otherwise, an interrupt could be handled
350 between re-enabling interrupts and waiting for the next
351 one to occur, wasting as much as one clock tick worth of
354 See [IA32-v2a] "HLT", [IA32-v2b] "STI", and [IA32-v3] 7.7. */
359 /* Function used as the basis for a kernel thread. */
361 kernel_thread (thread_func *function, void *aux)
363 ASSERT (function != NULL);
365 intr_enable (); /* The scheduler runs with interrupts off. */
366 function (aux); /* Execute the thread function. */
367 thread_exit (); /* If function() returns, kill the thread. */
370 /* Returns the running thread. */
372 running_thread (void)
376 /* Copy the CPU's stack pointer into `esp', and then round that
377 down to the start of a page. Because `struct thread' is
378 always at the beginning of a page and the stack pointer is
379 somewhere in the middle, this locates the curent thread. */
380 asm ("mov %%esp, %0" : "=g" (esp));
381 return pg_round_down (esp);
384 /* Returns true if T appears to point to a valid thread. */
386 is_thread (struct thread *t)
388 return t != NULL && t->magic == THREAD_MAGIC;
391 /* Does basic initialization of T as a blocked thread named
394 init_thread (struct thread *t, const char *name, int priority)
397 ASSERT (PRI_MIN <= priority && priority <= PRI_MAX);
398 ASSERT (name != NULL);
400 memset (t, 0, sizeof *t);
401 t->status = THREAD_BLOCKED;
402 strlcpy (t->name, name, sizeof t->name);
403 t->stack = (uint8_t *) t + PGSIZE;
404 t->priority = priority;
405 t->magic = THREAD_MAGIC;
408 /* Allocates a SIZE-byte frame at the top of thread T's stack and
409 returns a pointer to the frame's base. */
411 alloc_frame (struct thread *t, size_t size)
413 /* Stack data is always allocated in word-size units. */
414 ASSERT (is_thread (t));
415 ASSERT (size % sizeof (uint32_t) == 0);
421 /* Chooses and returns the next thread to be scheduled. Should
422 return a thread from the run queue, unless the run queue is
423 empty. (If the running thread can continue running, then it
424 will be in the run queue.) If the run queue is empty, return
426 static struct thread *
427 next_thread_to_run (void)
429 if (list_empty (&ready_list))
432 return list_entry (list_pop_front (&ready_list), struct thread, elem);
435 /* Completes a thread switch by activating the new thread's page
436 tables, and, if the previous thread is dying, destroying it.
438 At this function's invocation, we just switched from thread
439 PREV, the new thread is already running, and interrupts are
440 still disabled. This function is normally invoked by
441 thread_schedule() as its final action before returning, but
442 the first time a thread is scheduled it is called by
443 switch_entry() (see switch.S).
445 It's not safe to call printf() until the thread switch is
446 complete. In practice that means that printf()s should be
447 added at the end of the function.
449 After this function and its caller returns, the thread switch
452 schedule_tail (struct thread *prev)
454 struct thread *cur = running_thread ();
456 ASSERT (intr_get_level () == INTR_OFF);
458 /* Mark us as running. */
459 cur->status = THREAD_RUNNING;
461 /* Start new time slice. */
465 /* Activate the new address space. */
469 /* If the thread we switched from is dying, destroy its struct
470 thread. This must happen late so that thread_exit() doesn't
471 pull out the rug under itself. */
472 if (prev != NULL && prev->status == THREAD_DYING)
474 ASSERT (prev != cur);
475 if (prev != initial_thread)
476 palloc_free_page (prev);
480 /* Schedules a new process. At entry, interrupts must be off and
481 the running process's state must have been changed from
482 running to some other state. This function finds another
483 thread to run and switches to it.
485 It's not safe to call printf() until schedule_tail() has
490 struct thread *cur = running_thread ();
491 struct thread *next = next_thread_to_run ();
492 struct thread *prev = NULL;
494 ASSERT (intr_get_level () == INTR_OFF);
495 ASSERT (cur->status != THREAD_RUNNING);
496 ASSERT (is_thread (next));
499 prev = switch_threads (cur, next);
500 schedule_tail (prev);
503 /* Returns a tid to use for a new thread. */
507 static tid_t next_tid = 1;
510 lock_acquire (&tid_lock);
512 lock_release (&tid_lock);
517 /* Offset of `stack' member within `struct thread'.
518 Used by switch.S, which can't figure it out on its own. */
519 uint32_t thread_stack_ofs = offsetof (struct thread, stack);