Question

我有一个多线程C程序，其中一个线程创建随机时间和数字，并将它们存储在已排序的链表中，第二个线程将第一个节点中的时间与当前系统时间进行比较，并在每次删除节点时删除该节点时间平等。但是，0 0首先被添加到链表中，我找不到位置。据我所知，它没有被添加到插入函数中。任何帮助将不胜感激。以下是相关代码：

#include <pthread.h> 
#include <stdio.h>
#include <stdlib.h> 
#include <unistd.h> 
#include <time.h>
#include <signal.h> 

pthread_mutex_t count_mutex;

/* Link list node */
struct node
{
    int roomNo;
    time_t time;
    struct node* next;
};

void printList(struct node *node)
{
  while(node!=NULL)
  {
    printf("%d ", node->roomNo);
    printf("%d\n ", node->time);
    node = node->next;
  }
}

/* Function to insert a node at the beginging of the linked list */
void insert(struct node** head_ref, int new_room, time_t new_time)
{
  /* allocate node */
  struct node* new_node =
  (struct node*) malloc(sizeof(struct node));

  /* put in the data  */
  new_node->roomNo  = new_room;
  new_node->time  = new_time;

  /* link the old list off the new node */
  new_node->next = (*head_ref);    

  /* move the head to point to the new node */
  (*head_ref)    = new_node;
    MergeSort(&(*head_ref));
} 


/* sorts the linked list by changing next pointers (not data) */
void MergeSort(struct node** headRef)
{
  struct node* head = *headRef;
  struct node* a;
  struct node* b;

  /* Base case -- length 0 or 1 */
  if ((head == NULL) || (head->next == NULL))
  {
     return;
  }

    /* Split head into 'a' and 'b' sublists */
  FrontBackSplit(head, &a, &b); 

  /* Recursively sort the sublists */
  MergeSort(&a);
  MergeSort(&b);

  /* answer = merge the two sorted lists together */
  *headRef = SortedMerge(a, b);
}


struct node* SortedMerge(struct node* a, struct node* b)
{
  struct node* result = NULL;

  /* Base cases */
  if (a == NULL)
    return(b);
  else if (b==NULL)
    return(a);

  /* Pick either a or b, and recur */
  if (a->time <= b->time)
  {
    result = a;
    result->next = SortedMerge(a->next, b);
  }
  else
  {
    result = b;
    result->next = SortedMerge(a, b->next);
  }
  return(result);
 }


void FrontBackSplit(struct node* source,
                     struct node** frontRef, struct node** backRef)
{
  struct node* fast;
  struct node* slow;
  if (source==NULL || source->next==NULL)
  {
    /* length < 2 cases */
    *frontRef = source;
    *backRef = NULL;
  }
  else
  {
    slow = source;
    fast = source->next;

    /* Advance 'fast' two nodes, and advance 'slow' one node */
    while (fast != NULL)
    {
       fast = fast->next;
      if (fast != NULL)
      {
        slow = slow->next;
        fast = fast->next;
      }
    }

    /* 'slow' is before the midpoint in the list, so split it in two
     at that point. */
    *frontRef = source;
    *backRef = slow->next;
    slow->next = NULL;
  }
}

void * addThread(void *n) 
{  
  struct node *llnode = n;
  int i;
        for(i = 0; i <4; i++)
    { 
             pthread_mutex_lock(&count_mutex);
             printf("Adding node.\n");
             insert(&llnode, getRandRoom(), getRandTime());
     sleep(1);
             printf("the list is...\n");
             printList(llnode);
             pthread_mutex_unlock(&count_mutex);
    }
}

struct node* head;

int main()
{
    signal(SIGINT, ctrlc_catch);

    pthread_t addWakeup, makeWakeup;

    pthread_create(&addWakeup, NULL, addThread, (void*)&head);
    pthread_create(&makeWakeup, NULL, wakeThread, (void*)&head);

    pthread_join(addWakeup, NULL);
    pthread_join(makeWakeup, NULL);

      return 0;
}

示例输出是：

Adding node.
the list is...
0 0
 4000 1323882918
 Adding node.
the list is...
 0 0
 809 1323882890
 4000 1323882918
 Adding node.
the list is...
0 0
 809 1323882890
 7617 1323882908
 4000 1323882918
 Adding node.
the list is...
0 0
 809 1323882890
 7617 1323882908
 4000 1323882918
 4426 1323882926

Answer 1

虽然它可能存在于未显示的代码中，但代码可能需要调用pthread_mutex_init来初始化互斥锁。有可能变量count_mutex的内容“偶然”初始化为实际可行的值，但依靠它是不好的。

Answer 2

您的函数addthread创建其参数llnode的本地副本n，并使用指向llnode的指针来调用insert（）。插入可以更改llnode，但该更改只会影响本地副本。

您应该更改addThread以采用struct node**类型的参数，而不是struct node*。

Answer 3

你的问题很可能是由于将head（即〜struct node**）而不是head（即struct node*）的地址传递给线程函数{{1}是void *的类型转换。将此致电struct node*更改为pthread_create(&addWakeup, NULL, addThread, (void*)&head);＆amp;下一次打电话也是类似的。 很遗憾你当前没有看到崩溃。在我的系统上，我发现将pthread_create(&addWakeup, NULL, addThread, (void*)head);初始化为head会导致程序崩溃。 @wildplasser已经提供了类似的建议。尝试更改并检查打印的列表希望这有帮助！

C中的链表 - 第一个节点数据不正确，无法弄明白

3 个答案: