多线的的同步—条件变量

//reader_writer.c

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

/* 写者写完通知读者去读
读者读完通知写者去写 */

typedef struct{
    int value;
    
    int r_wait;
    pthread_mutex_t r_mutex;
    pthread_cond_t r_cond;
    
    int w_wait;
    pthread_mutex_t w_mutex;
    pthread_cond_t w_cond;
}Storage;

void set_value(Storage *s, int value)
{
    s->value = value;
}

int get_value(Storage *s)
{
    return s->value;
}

void *set_fn(void *arg)
{
    Storage *s = (Storage *)arg;
    int i = 0;
    for(; i < 100; i++){
        set_value(s, i+100);
        printf("writer write %d\n",i+100);
        pthread_mutex_lock(&s->r_mutex);
        //判断读者是否调用wait函数，如果调用了wait函数，那么写者就调用broadcast唤醒读者
        while(s->r_wait == 0){
            pthread_mutex_unlock(&s->r_mutex);
            sleep(1);
            pthread_mutex_lock(&s->r_mutex);
        }
        s->r_wait = 0;
        pthread_mutex_unlock(&s->r_mutex);
        pthread_cond_broadcast(&s->r_cond);
        
        //设置写者调用了wait函数，等待读者通知
        pthread_mutex_lock(&s->w_mutex);
        s->w_wait = 1;
        pthread_cond_wait(&s->w_cond, &s->w_mutex);
        pthread_mutex_unlock(&s->w_mutex);
    }
    
    return (void *)0;
}

void *get_fn(void *arg)
{
    Storage *s = (Storage *)arg;
    int i = 0;
    for(; i < 100; i++){
        //设置读者调用了wait函数，等待写者通知（r_wait和读者的wait函数绑定，1表示调用了wait函数）
        pthread_mutex_lock(&s->r_mutex);
        s->r_wait = 1;
        pthread_cond_wait(&s->r_cond, &s->r_mutex);
        pthread_mutex_unlock(&s->r_mutex);
        printf("reader read %d\n",get_value(s));
        
        //读者通知写者再写
        pthread_mutex_lock(&s->w_mutex);
        while(s->w_wait == 0){
            pthread_mutex_unlock(&s->w_mutex);
            sleep(1);
            pthread_mutex_lock(&s->w_mutex);
        }
        s->w_wait = 0;
        pthread_mutex_unlock(&s->w_mutex);
        pthread_cond_broadcast(&s->w_cond);
    }
    
    return (void *)0;
}

int main()
{
    pthread_t reader,writer;
    
    Storage s;
    s.r_wait = 0;
    pthread_mutex_init(&s.r_mutex, NULL);
    pthread_cond_init(&s.r_cond, NULL);
    
    s.w_wait = 0;
    pthread_mutex_init(&s.w_mutex, NULL);
    pthread_cond_init(&s.w_cond, NULL);
    
    if(pthread_create(&reader, NULL, get_fn, (void *)&s) < 0){
        printf("pthread_create failed\n");
    }
    
    if(pthread_create(&writer, NULL, set_fn, (void *)&s) < 0){
        printf("pthread_create failed\n");
    }
    
    pthread_join(reader, NULL);
    pthread_join(writer, NULL);
    
    pthread_mutex_destroy(&s.r_mutex);
    pthread_mutex_destroy(&s.w_mutex);
    
    pthread_cond_destroy(&s.r_cond);
    pthread_cond_destroy(&s.w_cond);
    
    return 0;
}