线程与读写锁

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


pthread_rwlock_t lock;

void *write1(void *arg)
{
    pthread_rwlock_wrlock(&lock);
    puts("write1");
    pthread_rwlock_unlock(&lock);

    return NULL;
}

void *read1(void *arg)
{
    pthread_rwlock_rdlock(&lock);
    puts("read1");
    sleep(2);
    pthread_rwlock_unlock(&lock);
    return NULL;
}

void *read2(void *arg)
{
    pthread_rwlock_rdlock(&lock);
    puts("read2");
    pthread_rwlock_unlock(&lock);
    return NULL;
}

int main(void)
{
    pthread_t   th1,th2,th3;
    int         ret = 0;

    ret = pthread_rwlock_init(&lock,NULL);
    if( ret != 0 )
    {
        perror("pthread_rwlock_init");
        return -1;
    }

    ret = pthread_create(&th1,NULL,read1,NULL);
    if( ret != 0 )
    {
        perror("read1 ");
        return -2;
    }

    usleep(2000);

    ret = pthread_create(&th2,NULL,write1,NULL);
    if( ret != 0 )
    {
        perror("write1 ");
        return -3;
    }

    usleep(2000);

    ret = pthread_create(&th3,NULL,read2,NULL);
    if( ret != 0 )
    {
        perror("read2 ");
        return -4;
    }

    pthread_join(th1,NULL);
    pthread_join(th2,NULL);
    pthread_join(th3,NULL);
    pthread_rwlock_destroy(&lock);
    return 0;
}

读写锁特点：

1）多个读者可以同时进行读 
2）写者之间必须互斥 
3）写者与读者之间互斥 
4 ) 写者优先于读者（唤醒时优先考虑写者）

互斥锁特点： 
1 ) 一次只能一个线程拥有互斥锁，其他线程只有等待

读写锁实现了互斥锁。

---

转载地址