（3）读写锁

读写锁：

    在编译时必须是类似的语句：gcc -o test test.c -D_XOPEN_SOURCE=500 –lpthread

   定义：pthread_rwlock_t

初始化，销毁：

#include

int pthread_rwlock_init(pthread_rwlock_t *restrict rwlock,

const pthread_rwlockattr_t *restrict attr);

int pthread_rwlock_destroy(pthread_rwlock_t *rwlock);

Both return: 0 if OK, error number on failure

执行读写锁：

include

int pthread_rwlock_rdlock(pthread_rwlock_t *rwlock);

int pthread_rwlock_wrlock(pthread_rwlock_t *rwlock);

int pthread_rwlock_unlock(pthread_rwlock_t *rwlock);

int pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock);

int pthread_rwlock_trywrlock(pthread_rwlock_t *rwlock);

All return: 0 if OK, error number on failure

 

注意：对于读写锁一次只有一个线程占有一个写模式的读写锁，可以有多个线程拥有读模式的读写锁。

 

例程1：（注意程序可以同时读一个处以读模式下的读写锁）

#include

#include

#include

#include

 

pthread_rwlock_t flock;

char buf[512];

char str[4][30] = {"aaaaaaaaaaaaaaaaaaaa\n","bbbbbbbbbbbbbbbbbbbb\n",

       "cccccccccccccccccccc\n","dddddddddddddddddddd\n"};

void *

thr_fn1(void *arg)

{

 long i;

 for(i=0;i<2000000;i++)

 {

 pthread_rwlock_wrlock(&flock);

 strcpy(buf,str[i%4]);

 pthread_rwlock_unlock(&flock);

 }

}

 

void *

thr_fn2(void *arg)

{

 int i;

 for(i=0;i<10;i++)

{

 pthread_rwlock_rdlock(&flock);

 printf("thead 2 :%s", buf);

 pthread_rwlock_unlock(&flock);

 usleep(5);

}

}

void *

thr_fn3(void *arg)

{

 int i;

 for(i=0;i<10;i++)

{

 pthread_rwlock_rdlock(&flock);

 printf("thead 3 :%s", buf);

 pthread_rwlock_unlock(&flock);

 usleep(5);

}

}

 

 

int main()

{

 pthread_t tid1,tid2,tid3;

 int err;

 

 strcpy(buf,"hello,world!\n");

 pthread_rwlock_init(&flock,NULL);

 

 err=pthread_create(&tid1,NULL,thr_fn1,NULL);

 if(err!=0)

 printf("can't create thread 1:%s\n",strerror(err));

 err=pthread_create(&tid2,NULL,thr_fn2,NULL);

 if(err!=0)

 printf("can't create thread 2:%s\n",strerror(err));

 err=pthread_create(&tid3,NULL,thr_fn3,NULL);

 if(err!=0)

 printf("can't create thread 3:%s\n",strerror(err));

 

 pthread_join(tid1,NULL);

 pthread_join(tid2,NULL);

 pthread_join(tid3,NULL);

 

 pthread_rwlock_destroy(&flock);

return 0;

}

 

程序结果：

thead 2 :cccccccccccccccccccc

thead 3 :cccccccccccccccccccc

thead 2 :cccccccccccccccccccc

thead 3 :cccccccccccccccccccc

thead 2 :dddddddddddddddddddd

thead 3 :dddddddddddddddddddd

thead 2 :dddddddddddddddddddd

thead 3 :dddddddddddddddddddd

thead 2 :dddddddddddddddddddd

thead 3 :dddddddddddddddddddd

thead 2 :dddddddddddddddddddd

thead 3 :dddddddddddddddddddd

thead 2 :dddddddddddddddddddd

thead 3 :dddddddddddddddddddd

thead 2 :dddddddddddddddddddd

thead 3 :dddddddddddddddddddd

thead 2 :dddddddddddddddddddd

thead 3 :dddddddddddddddddddd

thead 2 :dddddddddddddddddddd

thead 3 :dddddddddddddddddddd