在linux下利用信号量实现一个写者线程多个读者线程

#include<pthread.h>
#include<string.h>
#include<stdlib.h>
#include<stdio.h>
#include<semaphore.h>
typedef struct
{
    int value;
    sem_t sem,semw;// 信号量要和共享资源相互"绑定"
    int sign;
}Storage;
void set_data(Storage *s,int value)
{
    s->value=value;
}

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

void* rd1_fn(void *arg)
{
    Storage *s=(Storage*)arg;
    int i=0;
    for(;i<100;i++)
    {
        sem_wait(&s->sem);//实现读线程与写线程的同步
        s->sign++;
        int value=get_data(s);
        sleep(3);
        printf("rd1(0x)%lx read data :%d
",pthread_self(),value);
        if(s->sign!=3)
        sem_post(&s->sem);//实现读线程之间的互斥
        else
        sem_post(&s->semw);//实现写线程与读线程的同步
//        usleep(100);
        sleep(4);
    }
    return (void*)0;
}
void* rd2_fn(void *arg)
{
    Storage *s=(Storage*)arg;
    int i=0;
    for(;i<100;i++)
    {
        sem_wait(&s->sem);
        s->sign++;
        int value=get_data(s);
        sleep(2);
        printf("rd2(0x)%lx read data :%d
",pthread_self(),value);
        if(s->sign!=3)
        sem_post(&s->sem);
        else
        sem_post(&s->semw);
    //    usleep(100);
        sleep(1);
    }
    return (void*)0;
}
void* rd3_fn(void *arg)
{
    Storage *s=(Storage*)arg;
    int i=0;
    for(;i<100;i++)
    {
        sem_wait(&s->sem);
        s->sign++;
        int value=get_data(s);
        sleep(1);
        printf("rd3(0x)%lx read data :%d
",pthread_self(),value);
        if(s->sign!=3)
        sem_post(&s->sem);
        else
        sem_post(&s->semw);
    //    usleep(100);
        sleep(2);
    }
    return (void*)0;
}

void* wt_fn(void *arg)
{
    Storage *s=(Storage*)arg;
    int i=0;
    for(;i<100;i++)
    {
        sem_wait(&s->semw);//实现for循环里写线程的互斥
        s->sign=0;
        set_data(s,i+100);
        sleep(1);
        printf("wt(0x)%lx wrote data :%d
",pthread_self(),i+100);
        sem_post(&s->sem);//实现写线程与读线程的同步
        sleep(3);
    //    sleep(5);
    }    
    return (void*)0;
}
int main(void)
{
    int err;
    pthread_t rd1,rd2,rd3,wt;
    Storage s;
    s.value=0;
    s.sign=0;
    sem_init(&s.sem,0,0);//初始化为0
    sem_init(&s.semw,0,1);//初始化为1
    pthread_create(&rd1,NULL,rd1_fn,(void*)&s);
    pthread_create(&rd2,NULL,rd2_fn,(void*)&s);
    pthread_create(&rd3,NULL,rd3_fn,(void*)&s);
    pthread_create(&wt,NULL,wt_fn,(void*)&s);
    pthread_join(rd1,NULL);
    pthread_join(rd2,NULL);
    pthread_join(rd3,NULL);
    pthread_join(wt,NULL);
    sem_destroy(&s.sem);
    sem_destroy(&s.semw);
    return 0;
}

利用两个信号量 实现了写者之间的互斥，读者之间的互斥，读者和写者之间的同步。 若要实现多个写者，只需按照多个读者的思路写即可。