c - 如何在 C 中使用 pthread 交替 5 个 0 值和 5 个 1 值？

Question

我有一个使用 C 语言的小作业，它用交替的 5 个 0 值(由一个线程写入)和 5 个 1 值(由第二个线程写入)填充大小为 30 的整数数组。

这是迄今为止我的代码:

#include <stdio.h>
#include <pthread.h>

 int count = 0;
 int oktogo = 1; //0 is false, 1 is true. For thread2 this is reversed.

  pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
  pthread_cond_t condition = PTHREAD_COND_INITIALIZER;

  void *start_thread_one()
  {
    int i;
     for (i=1;i<30;i++) {
        pthread_mutex_lock(&mutex);
        while (oktogo == 0)
           pthread_cond_wait(&condition, &mutex);
        count=0;
        printf("thread one: %d\n", count);
        oktogo = 0;
        pthread_mutex_unlock(&mutex);
        pthread_cond_signal(&condition);
    }
    pthread_exit(0);
    }

 void *start_thread_two()
 {
   int i;
    for(i=1;i<30;i++) {
       pthread_mutex_lock(&mutex);
       while (oktogo == 1)
           pthread_cond_wait(&condition, &mutex);
       count =1;
       printf("thread two: %d\n", count);
       oktogo = 1;
       pthread_mutex_unlock(&mutex);
       pthread_cond_signal(&condition);
   }
   pthread_exit(0);
 }

 int main ()
 {
  int count = 0;
  pthread_t p1,p2;

  pthread_create(&p1,NULL,(void *)start_thread_one,NULL);
  pthread_create(&p2,NULL,(void *)start_thread_two,NULL);

   pthread_join(p1,NULL);
   pthread_join(p2,NULL);

   return(0);
}

输出仅显示线程一的值为 0，然后线程二的值为 1。如何交替打印 5 个 0 值和 5 个 1 值，而不是逐一打印？

截图:

Answer 1

您的线程同步逻辑似乎没问题。

唯一的问题是，当您有机会[并让主线程]在加入线程后将其打印出来时，您实际上并没有将其存储到数组中。

此外，您实际上并不需要两个单独的线程函数。您可以使用一个参数/值为 0 或 1 的参数。也就是说，参数指定线程数组的起始偏移量、要存储的值以及 oktogo 所需的值>.

无论如何，这是一个工作版本:

#include <stdio.h>
#include <pthread.h>

int count = 0;
int oktogo = 0;                         // 0 is false, 1 is true. For thread2 this is reversed.

#define CHUNK       5
int array[5000];

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t condition = PTHREAD_COND_INITIALIZER;

void *
start_thread(void *ptr)
{
    long self = (long) ptr;
    int i;

    for (i = 1; i < 30; i++) {
        pthread_mutex_lock(&mutex);

        while (oktogo != self)
            pthread_cond_wait(&condition, &mutex);

        printf("thread %ld: %d\n",self,count);
        for (int idx = 0;  idx < CHUNK;  ++idx, ++count)
            array[count] = self;

        oktogo = ! self;
        pthread_mutex_unlock(&mutex);
        pthread_cond_signal(&condition);
    }

    pthread_exit(0);
}

int
main()
{
    int count = 0;
    pthread_t p1,
     p2;

    for (int idx = 0;  idx < sizeof(array) / sizeof(array[0]);  ++idx)
        array[idx] = -1;

    pthread_create(&p1, NULL, (void *) start_thread, (void *) 0);
    pthread_create(&p2, NULL, (void *) start_thread, (void *) 1);

    pthread_join(p1, NULL);
    pthread_join(p2, NULL);

    for (int idx = 0;  idx < sizeof(array) / sizeof(array[0]);  ++idx) {
        if (array[idx] >= 0)
            printf("%d: %d\n",idx,array[idx]);
    }

    return (0);
}