linux 读写锁-蒲公英云

linux 读写锁

悠悠 2022-03-12 06:16 290阅读 0赞

转载自https://www.cnblogs.com/wzben/p/5432518.html
读写锁是一个可以分写状态和读状态的锁，可以分别加上写状态或读状态的锁。在读模式的锁下，所有试图以读模式获得它进行加锁的线程都可以获得锁，所有希望以写模式获得它的都会被阻塞。在写模式下，读写锁都被阻塞。读写锁又成共享互斥锁。
简单的说，读模式的加锁下，所有进程都可以获得读锁，但都不能获得写锁。
在写模式下，读写锁就变成了互斥锁，只有一个线程可以获得锁。
例子：
4个线程，全都加锁，不释放锁。

#include <pthread.h> 
#include <semaphore.h>
#include <unistd.h> 
#include <stdio.h>
#include<fcntl.h>
#include <pthread.h>
#include <errno.h>
int index = 1;
pthread_rwlock_t rwlock;
pthread_mutex_t mutex;
void fun1(void){ 
    int i = 0;
    while(i<50){ 
    //if(pthread_mutex_trylock(&mutex)==0){ 
    if(pthread_rwlock_tryrdlock(&rwlock)==0){ 
    printf("In thread 1,lock,index is %d\n",index);
    //pthread_mutex_unlock(&mutex);never unlock
    }
    else
    printf("con not get lock in thread 1\n");
    if(pthread_rwlock_trywrlock(&rwlock)==EBUSY)
        printf("con not write in thread 1\n");
    i++;
    usleep(100);
    }
}
void fun2(void){ 
    int i = 0;
    while(i<50){ 
    //if(pthread_mutex_trylock(&mutex)==0){ 
    if(pthread_rwlock_tryrdlock(&rwlock)==0){ 
    printf("In thread 2,lock,index is %d\n",index);
    i++;
    //pthread_mutex_unlock(&mutex);never unlock
    }
    else
    printf("con not get lock in thread 2\n");
    if(pthread_rwlock_trywrlock(&rwlock)==EBUSY)
        printf("con not write in thread 2\n");
    i++;
    usleep(100);
    }
}
void fun3(void){ 
    int i = 0;
    while(i<50){ 
    //if(pthread_mutex_trylock(&mutex)==0){ 
    if(pthread_rwlock_tryrdlock(&rwlock)==0){ 
    printf("In thread 3,lock,index is %d\n",index);
    //pthread_mutex_unlock(&mutex);never unlock
    }
    else
    printf("con not get lock in thread 3\n");
    i++;
    if(pthread_rwlock_trywrlock(&rwlock)==EBUSY)
        printf("con not write in thread 3\n");
    usleep(100);
    }
}
void fun4(void){ 
    int i = 0;
    while(i<50){ 
    //if(pthread_mutex_trylock(&mutex)==0){ 
    if(pthread_rwlock_tryrdlock(&rwlock)==0){ 
    printf("In thread 4,lock,index is %d\n",index);
    }
    //pthread_mutex_unlock(&mutex);never unlock
    else
    printf("con not get lock in thread 4\n");
    if(pthread_rwlock_trywrlock(&rwlock)==EBUSY)
        printf("con not write in thread 4\n");
    i++;
    usleep(100);
    }
}
int main(){ 
    pthread_t tid1,tid2,tid3,tid4;
    pthread_mutex_init(&mutex,NULL);
    pthread_create(&tid1,NULL,(void*)fun1,NULL);
    pthread_create(&tid2,NULL,(void*)fun2,NULL);
    pthread_create(&tid3,NULL,(void*)fun3,NULL);
    pthread_create(&tid4,NULL,(void*)fun4,NULL);
    pthread_join(tid1,NULL);
    pthread_join(tid2,NULL);
    pthread_join(tid3,NULL);
    pthread_join(tid4,NULL);
}