操作系统读写锁

读写锁

pthread_rwlock_t rwlock = PTHREAD_RWLOCK_INITIALIZER;
功能：定义并初始化读写锁
​
int pthread_rwlock_init(pthread_rwlock_t *restrict rwlock,const pthread_rwlockattr_t *restrict attr);
功能：初始化读写锁
​
int pthread_rwlock_rdlock(pthread_rwlock_t *rwlock);
功能：加读锁，如果不能加则阻塞等待int pthread_rwlock_wrlock(pthread_rwlock_t *rwlock);
功能：加写锁，如果不能加则阻塞等待int pthread_rwlock_unlock(pthread_rwlock_t *rwlock);
功能：解读写锁。int pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock);
功能：尝试加读锁，如果不能加则立即返回
​
int pthread_rwlock_trywrlock(pthread_rwlock_t *rwlock);
功能：尝试加写锁，如果不能加则立即返回
​
int pthread_rwlock_timedrdlock(pthread_rwlock_t *restrict rwlock,const struct timespec *restrict abstime);
功能：带倒计时加读锁，超时则立即返回int pthread_rwlock_timedwrlock(pthread_rwlock_t *restrict rwlock,const struct timespec *restrict abstime);
功能：带倒计时加写锁，超时则立即返回
​
int pthread_rwlock_destroy(pthread_rwlock_t *rwlock);
功能：销毁读写锁使用读写锁的线程应根据后续的操作进行加锁，如果只对数据进行读取则只加读锁即可，只有对数据进行修改时才应该加写锁，与互斥锁的区别是，它能让只读的线程加上锁，使用原理与文件锁一样。线程A     线程B读锁      读锁  OK读锁      写锁  NO写锁      读锁  NO写锁      写锁  NO

练习：使用读写锁来解决同步问题。

#include <stdio.h>
#include <pthread.h>
​
pthread_rwlock_t rwlock = PTHREAD_RWLOCK_INITIALIZER;
​
int num = 0;
void* run(void* arg)
{for(int i=0; i<1000000; i++){pthread_rwlock_wrlock(&rwlock);num++;pthread_rwlock_unlock(&rwlock);}    
}
​
int main(int argc,const char* argv[])
{pthread_t tid1,tid2;pthread_create(&tid1,NULL,run,NULL);pthread_create(&tid2,NULL,run,NULL);pthread_join(tid1,NULL);pthread_join(tid2,NULL);pthread_rwlock_destroy(&rwlock);printf("%d\n",num);
}