Condition variables and mutexes supporting the use of routines-consumer, producer model

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

//链表的结点
struct msg
{
    
    
    int num; 
    struct msg *next; 
};
 
struct msg *head = NULL;    //头指针
struct msg *temp = NULL;    //节点指针

//静态方式初始化互斥锁和条件变量
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t has_producer = PTHREAD_COND_INITIALIZER;
 
void *producer(void *arg)
{
    
    
    while (1)   //线程正常不会解锁，除非收到终止信号
    {
    
    
        pthread_mutex_lock(&mutex);         //加锁

        temp = malloc(sizeof(struct msg));
        temp->num = rand() % 100 + 1;
        temp->next = head;
        head = temp;                        //头插法
        printf("---producered---%d\n", temp->num);

        pthread_mutex_unlock(&mutex);       //解锁
        pthread_cond_signal(&has_producer); //唤醒消费者线程
        usleep(rand() % 3000);              //为了使该线程放弃cpu,让结果看起来更加明显。
    }

    return NULL;
}

void *consumer(void *arg)
{
    
    
    while (1)       //线程正常不会解锁，除非收到终止信号
    {
    
    
        pthread_mutex_lock(&mutex);     //加锁
        while (head == NULL)            //如果共享区域没有数据，则解锁并等待条件变量
        {
    
    
            //没有数据就则处于等待状态。
            pthread_cond_wait(&has_producer, &mutex);   //我们通常在一个循环内使用该函数
        }
        temp = head;
        head = temp->next;
        printf("------------------consumer--%d\n", temp->num);
        free(temp);                     //删除节点，头删法
        temp = NULL;                    //防止野指针
        pthread_mutex_unlock(&mutex);   //解锁

        usleep(rand() % 3000);          //为了使该线程放弃cpu,让结果看起来更加明显。
    }
    return NULL;
}

int main(void)
{
    
    
    pthread_t ptid, ctid;
    srand(time(NULL));      //根据时间摇一个随机数种子

    //创建生产者和消费者线程
    pthread_create(&ptid, NULL, producer, NULL);
    pthread_create(&ctid, NULL, consumer, NULL);

    //主线程回收两个子线程
    pthread_join(ptid, NULL);
    pthread_join(ctid, NULL);
 
    return 0;
}
/*gcc cond3.c -o cond3 -lpthread*/

The use of condition variables can prevent the CPU from being in a polling state all the time and improve the lack of mutex.