条件变量解决生产者消费者问题

目录

1.条件变量函数原型

pthread_cond_init

pthread_cond_destroy

pthread_cond_wait

pthread_cond_timedwait

pthread_cond_signal

pthread_cond_broadcast

2.案例源码

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生产者消费者问题:生产者不能在容器满了继续生成，消费者不能在容器为空的时候消费

1.条件变量函数原型

条件变量的类型 pthread_cond_t

pthread_cond_init

int pthread_cond_init(pthread_cond_t *restrict cond, const pthread_condattr_t *restrict attr);

-功能:初始化

pthread_cond_destroy

int pthread_cond_destroy(pthread_cond_t *cond);

-功能:回收资源

pthread_cond_wait

 int pthread_cond_wait(pthread_cond_t *restrict cond, pthread_mutex_t *restrict mutex);

-功能:等待，调用了该函数，线程会阻塞。当这个函数调用阻塞的时候，会对互斥锁进行解锁，当不阻塞的，继续向下执行，会重新加锁。

pthread_cond_timedwait

int pthread_cond_timedwait(pthread_cond_t *restrict cond, pthread_mutex_t *restrict mutex, const struct timespec *restrict abstime);

-功能:等待多少时间，调用了这个函数，线程会阻塞，知道指定的时间结束。

pthread_cond_signal

int pthread_cond_signal(pthread_cond_t *cond);

-功能:唤醒一个或多个等待的线程

pthread_cond_broadcast

int pthread_cond_broadcast(pthread_cond_t *cond);

-功能:唤醒所有的等待的线程

2.案例源码

通过设置条件变量来在没有资料的时候消费者等待生产者来生成

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

//创建互斥量
pthread_mutex_t mutex;
//创建条件变量
pthread_cond_t cond;

struct Node{
    int num;
    struct Node *next;
};

//头节点
struct Node *head=NULL;

void *producer(void *arg){
    //不断创建新的节点，添加到链表中
    while(1){
        pthread_mutex_lock(&mutex);
        struct Node * newNode = (struct Node *)malloc(sizeof(struct Node));
        newNode->next=head;
        head=newNode;
        newNode->num=rand()%1000;
        printf("add node, num %d,tid :%ld\n",newNode->num,pthread_self());

        //只要生成了一个，就通知消费者消费
        pthread_cond_signal(&cond);

        pthread_mutex_unlock(&mutex);
        usleep(100);
    }
    return NULL;
}

void *customer(void *arg){
    while(1){
        pthread_mutex_lock(&mutex);
        //保存头节点的指针
        struct Node* tmp=head;
        if(head!=NULL){
            head=head->next;
            printf("del node, num:%d,tid:%ld\n",tmp->num,pthread_self());
            free(tmp);
            pthread_mutex_unlock(&mutex);
            usleep(100);
        }else{
            pthread_cond_wait(&cond,&mutex);
            pthread_mutex_unlock(&mutex);
        }
    }
    return NULL;
}
int main(){

    pthread_mutex_init(&mutex,NULL);
    pthread_cond_init(&cond,NULL);

    //创建5个生产者线程和5个消费者线程
    pthread_t ptids[5],ctids[5];
    for(int i=0;i<5;i++){
        pthread_create(&ptids[i],NULL,producer,NULL);
        pthread_create(&ctids[i],NULL,customer,NULL);
    }

    for(int i=0;i<5;i++){
        pthread_detach(ptids[i]);
        pthread_detach(ptids[i]);
    }

    while(1){
        sleep(10);
    }

    pthread_mutex_destroy(&mutex);
    pthread_cond_destroy(&cond);

    pthread_exit(NULL);
    return 0;
}