使用线程同步打印数字的顺序

2023-09-23 10:40:58 学习 3次阅读 投稿:佚名
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在这里,我们将看到如何使用不同的线程按正确的顺序打印数字。在这里,我们将创建n个线程,然后对它们进行同步。思路是,第一个线程将打印1,然后第二个线程将打印2,依此类推。当一个线程尝试打印时,它将锁定资源,因此其他线程无法使用该部分。

示例

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t* cond = NULL;
int threads;
volatile int count = 0;
void* sync_thread(void* num) { //this function is used to synchronize the threads
   int thread_number = *(int*)num;
   while (1) {
      pthread_mutex_lock(&mutex); //lock the section
      if (thread_number != count) { //if the thread number is not same as count, put all thread
          except one into waiting state
         pthread_cond_wait(&cond[thread_number], &mutex);
      }
      printf("%d ", thread_number + 1); //print the thread number
         count = (count+1)%(threads);
      // notify the next thread
      pthread_cond_signal(&cond[count]);
      pthread_mutex_unlock(&mutex);
   }
   return NULL;
}
int main() {
   pthread_t* thread_id;
   volatile int i;
   int* thread_arr;
   printf("

Enter number of threads: "); scanf("%d", &threads); // allocate memory to cond (conditional variable) thread id's and array of size threads cond = (pthread_cond_t*)malloc(sizeof(pthread_cond_t) * threads); thread_id = (pthread_t*)malloc(sizeof(pthread_t) * threads); thread_arr = (int*)malloc(sizeof(int) * threads); for (i = 0; i < threads; i++) { //create threads thread_arr[i] = i; pthread_create(&thread_id[i], NULL, sync_thread, (void*)&thread_arr[i]); } // waiting for thread for (i = 0; i < threads; i++) { pthread_join(thread_id[i], NULL); } return 0; }

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输出

$ g++ test.cpp -lpthread
$ ./a.out

Enter number of threads: 5
1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3
4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5
1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3
4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1
2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4
5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2
3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5
...
...
...
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