linux 读写锁应用实例

转自：http://blog.csdn.net/dsg333/article/details/22113489

/*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>

static pthread_rwlock_t rwlock;//读写锁对象

#define WORK_SIZE 1024
char work_area[WORK_SIZE];
int time_to_exit;

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);
    }
  
    pthread_rwlock_destroy(&rwlock);//销毁读写锁               
    exit(EXIT_SUCCESS);
}

void *thread_function_read_o(void *arg)
{
    printf("thread read one try to get lock\n");   
   
    pthread_rwlock_rdlock(&rwlock);//获取读取锁
    while(strncmp("end", work_area, 3) != 0)
    {
        printf("this is thread read one.");
        printf("the characters is %s",work_area);   
        pthread_rwlock_unlock(&rwlock);           
        sleep(2);
        pthread_rwlock_rdlock(&rwlock);       
        while (work_area[0] == '\0' )          
        {
            pthread_rwlock_unlock(&rwlock);   
            sleep(2);
            pthread_rwlock_rdlock(&rwlock);
        }
    }   
    pthread_rwlock_unlock(&rwlock);   
    time_to_exit=1;
    pthread_exit(0);
}

void *thread_function_read_t(void *arg)
{
    printf("thread read one try to get lock\n");
    pthread_rwlock_rdlock(&rwlock);
    while(strncmp("end", work_area, 3) != 0)
    {
        printf("this is thread read two.");
        printf("the characters is %s",work_area);   
        pthread_rwlock_unlock(&rwlock);           
        sleep(5);
        pthread_rwlock_rdlock(&rwlock);           
        while (work_area[0] == '\0' )          
        {               
            pthread_rwlock_unlock(&rwlock);   
            sleep(5);
            pthread_rwlock_rdlock(&rwlock);   
        }
    }
    pthread_rwlock_unlock(&rwlock);   
    time_to_exit=1;
    pthread_exit(0);
}

void *thread_function_write_o(void *arg)
{
    printf("this is write thread one try to get lock\n");
    while(!time_to_exit)
    {
        pthread_rwlock_wrlock(&rwlock);
        printf("this is write thread one.\nInput some text. Enter 'end' to finish\n");
        fgets(work_area, WORK_SIZE, stdin);
        pthread_rwlock_unlock(&rwlock);
        sleep(15);
    }
    pthread_rwlock_unlock(&rwlock);
    pthread_exit(0);
}

void *thread_function_write_t(void *arg)
{
    sleep(10);
    while(!time_to_exit)
    {
        pthread_rwlock_wrlock(&rwlock);//获取写入锁
        printf("this is write thread two.\nInput some text. Enter 'end' to finish\n");
        fgets(work_area, WORK_SIZE, stdin);//写入
        pthread_rwlock_unlock(&rwlock);//解锁
        sleep(20);
    }
    pthread_rwlock_unlock(&rwlock);//解锁
    pthread_exit(0);
}