读写锁的简单示例

/*使用读写锁实现四个线程读写一段程序的实例，共创建了四个新的线程，其中两个线程用来读取数据，另外两个线程用来写入数据。在任意时刻，如果有一个线程在写数据，将阻塞所有其他线程的任何操作。*/
#include <errno.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <bits/pthreadtypes.h>
pthread_rwlock_t rwlock;//读写锁对象
int a=0;
void *thread_function_read_o(void *arg);//读线程1
void *thread_function_read_t(void *arg);//读线程2
void *thread_function_write_o(void *arg);//写线程1
void *thread_function_write_t(void *arg);//写线程2
   

int main(int argc,char *argv[])
{
    int res;
    pthread_t a_thread,b_thread,c_thread,d_thread;
    void *thread_result;

    res=pthread_rwlock_init(&rwlock,NULL);//初始化读写锁
    if (res != 0)
    {
        perror("rwlock initialization failed");
        exit(EXIT_FAILURE);
    }
    res = pthread_create(&a_thread, NULL, thread_function_read_o, NULL);//create new thread创建线程
    if (res != 0)
    {
        perror("Thread creation failed");
        exit(EXIT_FAILURE);
    }

     res = pthread_create(&b_thread, NULL, thread_function_read_t, NULL);//create new thread
    if (res != 0)
    {
        perror("Thread creation failed");
        exit(EXIT_FAILURE);
    }
    res = pthread_create(&c_thread, NULL, thread_function_write_o, NULL);//create new thread
    if (res != 0)
    {
        perror("Thread creation failed");
        exit(EXIT_FAILURE);
    }
    res = pthread_create(&d_thread, NULL, thread_function_write_t, NULL);//create new thread
    if (res != 0)
    {
        perror("Thread creation failed");
        exit(EXIT_FAILURE);
    }
   
     res = pthread_join(a_thread, &thread_result);//等待a_thread线程结束           
     if (res != 0)
     {
         perror("Thread join failed");
         exit(EXIT_FAILURE);
     }
     res = pthread_join(b_thread, &thread_result);           
    if (res != 0)
     {
         perror("Thread join failed");
         exit(EXIT_FAILURE);
     }
    res = pthread_join(c_thread, &thread_result);           
    if (res != 0)
    {
        perror("Thread join failed");
        exit(EXIT_FAILURE);
    }
    res = pthread_join(d_thread, &thread_result);           
    if (res != 0)
    {
       perror("Thread join failed");
       exit(EXIT_FAILURE);
    }
  
    res = pthread_rwlock_destroy(&rwlock);//销毁读写锁               
    if (res != 0)
    {
       perror("rwlock destory failed");
       exit(EXIT_FAILURE);
    }
}

void *thread_function_read_o(void *arg)
{   pthread_rwlock_rdlock(&rwlock);//获取读取锁
    printf("this is read thread1 get lock
");  
    sleep(10);
    printf("read thread1:%d
",a);
    pthread_rwlock_unlock(&rwlock);   
    pthread_exit(0);
}

 void *thread_function_read_t(void *arg)
{   pthread_rwlock_rdlock(&rwlock);
    printf("this is read thread2 get lock
");
    sleep(10);
    printf("read thread2:%d
",a);
    pthread_rwlock_unlock(&rwlock);   
    pthread_exit(0);
}

void *thread_function_write_o(void *arg)
{
        pthread_rwlock_wrlock(&rwlock);//获取写入锁
        printf("this is write thread1 get lock
");
        sleep(5);
        a++;
        printf("write thread1:%d
",a);
        pthread_rwlock_unlock(&rwlock);//解锁
        pthread_exit(0);
}

void *thread_function_write_t(void *arg)
{      
        pthread_rwlock_wrlock(&rwlock);//获取写入锁
        printf("this is write thread2 get lock
");
        a+=2;
        sleep(5);
        printf("write thread2:%d
",a);
        pthread_rwlock_unlock(&rwlock);//解锁
        pthread_exit(0);
}
程序中加的sleep仅仅是为了验证，同一时间只能有一个线程可以获取写入锁，但是可以有多个读者可以获取读取锁！