线程与读写锁

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#include <pthread.h>#include <stdio.h>pthread_rwlock_t lock;void * write1(void *arg){    pthread_rwlock_wrlock(&lock);    puts("write1");    pthread_rwlock_unlock(&lock);    return((void *)1);}void *write2(void *arg){    pthread_rwlock_wrlock(&lock);    puts("write2");    pthread_rwlock_unlock(&lock);    return((void *)2);}void *read1(void *arg){    pthread_rwlock_rdlock(&lock);    puts("read1");    sleep(10);    pthread_rwlock_unlock(&lock);    return((void *)3);}void *read2(void *arg){    pthread_rwlock_rdlock(&lock);    puts("read2");    pthread_rwlock_unlock(&lock);    return((void *)3);}int main(void){    pthread_t   th1,th2,th3,th4;    int         ret;    ret =pthread_create(&th1,NULL,write1,NULL);    if( ret != 0 )    {        perror("pthread1 ");        return 0;    }    usleep(1000);    ret = pthread_create(&th3,NULL,read1,NULL);    if( ret != 0 )    {        perror("pthread3 ");        return 0;    }    usleep(1000);    ret = pthread_create(&th4,NULL,read2,NULL);    if( ret != 0 )    {        perror("pthread4 ");        return 0;    }    usleep(1000);    ret = pthread_create(&th2,NULL,write2,NULL);    if( ret != 0 )    {        perror("pthread2 ");        return 0;    }    pthread_join(th3,NULL);    pthread_rwlock_destroy(&lock);    return 1;}

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

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