分析了一下Mission 1中的代码，现在我们来开始正式实现。

 

首先，给线程结构体 struct thread{}加上ticks_blocked成员，在threads/thread.h中

　　

/* Record the time the thread has been blocked. */    int64_t ticks_blocked;

在线程创建的时候，ticks_blocked应该被初始化为0，在threads/thread.c中，找到thread_create()函数，添加如下代码：

/*Set default ticks_blocked ＝ 0*/  t->ticks_blocked = 0;

修改timer_sleep()函数：

/* Sleeps for approximately TICKS timer ticks.  Interrupts must   be turned on. */voidtimer_sleep (int64_t ticks){  if (ticks <= 0)  {    return;  }  ASSERT (intr_get_level () == INTR_ON);  enum intr_level old_level = intr_disable ();  struct thread *current_thread = thread_current ();  current_thread->ticks_blocked = ticks;  thread_block ();  intr_set_level (old_level);}

在这里我们调用了一个thread_block()函数，在threads/thread.c中修改：

/* Puts the current thread to sleep.  It will not be scheduled   again until awoken by thread_unblock().   This function must be called with interrupts turned off.  It   is usually a better idea to use one of the synchronization   primitives in synch.h. */voidthread_block (void){  ASSERT (!intr_context ());  ASSERT (intr_get_level () == INTR_OFF);  thread_current ()->status = THREAD_BLOCKED;  schedule ();}

然后，修改时钟中断处理函数，找到devices/timer.中的timer_interrupt()函数，添加代码

thread_foreach (blocked_thread_check, NULL);

这里的thread_foreach()函数，即对每个函数都执行blocked_thread_check()，在threads/thread.c中修改。

/* Invoke function 'func' on all threads, passing along 'aux'.   This function must be called with interrupts off. */voidthread_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);    }}

最后，给thread添加一个blocked_thread_check()方法：

先声明

void blocked_thread_check (struct thread *, void * UNUSED);

然后在thread.c中添加：

/* Check the blocked thread */voidblocked_thread_check (struct thread *t, void *aux UNUSED){  if (t->status == THREAD_BLOCKED && t->ticks_blocked > 0)  {      t->ticks_blocked--;      if (t->ticks_blocked == 0)      {          thread_unblock(t);      }  }}

这里又修改了一个thread_unblock()函数，作用是将线程丢到ready队列中：

/* 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.)   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. */voidthread_unblock (struct thread *t){  enum intr_level old_level;  ASSERT (is_thread (t));  old_level = intr_disable ();  ASSERT (t->status == THREAD_BLOCKED);  list_push_back (&ready_list, &t->elem);  t->status = THREAD_READY;  intr_set_level (old_level);}

这样一来，timer_sleep()的唤醒机制我们就实现了，将更改过的代码push上去。

中间发现自己犯了几个小错误，fix bug之后才跑通。

具体的代码可以在我的Github中找到。