使用线程同步顺序打印数字
在这里，我们将看到如何使用不同的线程以正确的顺序打印数字。在这里，我们将创建n个线程，然后对其进行同步。这个想法是，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，因此没有线程可以使用该部分。
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);
//通知下一个线程
pthread_cond_signal(&cond[count]);
pthread_mutex_unlock(&mutex);
}
return NULL;
}
int main() {
pthread_t* thread_id;
volatile int i;
int* thread_arr;
printf("\nEnter number of threads: ");
scanf("%d", &threads);
//将内存分配给cond（条件变量）线程ID和大小线程数组
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]);
}
//等待线程
for (i = 0; i < threads; i++) {
pthread_join(thread_id[i], NULL);
}
return 0;
}
输出结果
$ 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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