1. struct thread 요소 추가 o

include/threads/thread.h

• 정답

  struct thread
    {
      ...
      int init_priority;
      
      struct lock *wait_on_lock;
      struct list donations;
      struct list_elem donation_elem;
  	...
    };
  

• 구현 = 최종코드

  struct thread
  {
  	/* Owned by thread.c. */
  	tid_t tid;				   /* Thread identifier. */
  	enum thread_status status; /* Thread state. */
  	char name[16];			   /* Name (for debugging purposes). */
  	int priority;			   /* Priority. */
  
  	/* Shared between thread.c and synch.c. */
  	struct list_elem elem; /* List element. */
  	/*----------------[project1]-------------------*/
  	/* local tick */
  	int64_t wake_up_tick;
  
  	/* priority donaion 관련 element 추가 */
  	int init_priority;					// donation이후 우선순위를 초기화하기 위해 초기값 저장
  	struct lock *wait_on_lock;			// 해당 스레드가 대기하고 있는 lock자료구조 주소 저장
  	struct list donations;				// multiple donation 을 고려하기 위해사용
  	struct list_elem donation_elem;		// multiple donation 을 고려하기 위해사용
  	/*----------------[project1]-------------------*/
  #ifdef USERPROG
  	/* Owned by userprog/process.c. */
  	uint64_t *pml4; /* Page map level 4 */
  #endif
  #ifdef VM
  	/* Table for whole virtual memory owned by thread. */
  	struct supplemental_page_table spt;
  #endif
  
  	/* Owned by thread.c. */
  	struct intr_frame tf; /* Information for switching */
  	unsigned magic;		  /* Detects stack overflow. */
  };
  

2. 추가한 요소 초기화 o

thread/thread.c

• 정답

  static void
  init_thread (struct thread *t, const char *name, int priority)
  {
    ...
    t->init_priority = priority;
    t->wait_on_lock = NULL;
    list_init (&t->donations);
    ...
  }
  

• 구현 = 최종코드

  static void
  init_thread(struct thread *t, const char *name, int priority)
  {
  	ASSERT(t != NULL);
  	ASSERT(PRI_MIN <= priority && priority <= PRI_MAX);
  	ASSERT(name != NULL);
  
  	memset(t, 0, sizeof *t);
  	t->status = THREAD_BLOCKED;
  	strlcpy(t->name, name, sizeof t->name);
  	t->tf.rsp = (uint64_t)t + PGSIZE - sizeof(void *);
  	t->priority = priority;
  	t->magic = THREAD_MAGIC;
  	/*----------------[project1]-------------------*/
  	t->init_priority = priority;
  	t->wait_on_lock = NULL;
  	list_init(&t->donations);
  	/*----------------[project1]-------------------*/
  }
  

3. lock_acquire ()함수 수정

threads/synch.c

• default

  void
  lock_acquire (struct lock *lock)
  {
    ASSERT (lock != NULL);
    ASSERT (!intr_context ());
    ASSERT (!lock_held_by_current_thread (lock));
  
    sema_down (&lock->semaphore);
    lock->holder = thread_current ();
  }
  

• 정답

  void
  lock_acquire (struct lock *lock)
  {
    ASSERT (lock != NULL);
    ASSERT (!intr_context ());
    ASSERT (!lock_held_by_current_thread (lock));
  
    struct thread *cur = thread_current ();
    if (lock->holder) {
      cur->wait_on_lock = lock;
      list_insert_ordered (&lock->holder->donations, &cur->donation_elem, 
      			thread_compare_donate_priority, 0);
      donate_priority ();
    }
  
    sema_down (&lock->semaphore);
    
    cur->wait_on_lock = NULL;
    lock->holder = cur;
  }
  

• 구현1

  void lock_acquire(struct lock *lock)
  {
  	ASSERT(lock != NULL);
  	ASSERT(!intr_context());
  	ASSERT(!lock_held_by_current_thread(lock));
  
  	if (lock->holder) //lock->holder가 있다면,
  	{
  		struct thread *cur_t = thread_current();
  
  		cur_t->wait_on_lock = &lock; //내가 필요한 lock을 기록
  		cur_t->init_priority = cur_t->priority; //donation받기 전, 내 원래 priority기록
  		donate_priority(); //도네이션 해서 lock빨리써서 내놔라.
  	}
  
  	sema_down(&lock->semaphore); 			// lock쓰기
  	thread_current()->wait_on_lock = NULL;  //기다리는 lock없으므로 wait_on_lock 초기화
  	lock->holder = thread_current();		// 현재 thread가 lock->holder가 되는 것
  }
  

  차이: donate_priority()함수에서 list_insert_ordered()를 사용

• 최종코드

  void lock_acquire(struct lock *lock)
  {
  	ASSERT(lock != NULL);
  	ASSERT(!intr_context());
  	ASSERT(!lock_held_by_current_thread(lock));
  
  	struct thread *cur_t = thread_current();
  
  	if (lock->holder != NULL)
  	{
  		cur_t->wait_on_lock = lock;
  		// cur_t->init_priority = cur_t->priority; 🤔
  		list_insert_ordered(&lock->holder->donations, &cur_t->donation_elem,
  							donate_priority_less, 0); // 추가 🤔
  		donate_priority();
  	}
  
  	sema_down(&lock->semaphore);
  	cur_t->wait_on_lock = NULL;
  	lock->holder = thread_current();
  }
  

4. thread_compare_donate_priority()구현 x

thread/thread.c

• 정답

  bool
  thread_compare_donate_priority (const struct list_elem *l, 
  				const struct list_elem *s, void *aux UNUSED)
  {
  	return list_entry (l, struct thread, donation_elem)->priority
  		 > list_entry (s, struct thread, donation_elem)->priority;
  }
  

• 구현1

  다른 함수에서 비교하긴 했으나, 이전에 구현한 priority_less함수 사용.