多线程读写锁机制

#include <stdio.h>
#include <pthread.h>
#include <stdio.h>
#include <errno.h>
#include <stdlib.h>
static pthread_rwlock_t rwlock;
#define WORK_SIZE 1024
char work_area[WORK_SIZE];
int time_to_exit=0;

void *thread_function_read_o(void *arg);
void *thread_function_read_t(void *arg);
void *thread_function_write_o(void *arg);
void *thread_function_write_t(void *arg);

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);
    if(res!=0)
        exit(EXIT_FAILURE);
    res=pthread_create(&a_thread,NULL,thread_function_read_o,NULL);
    if(res!=0)
        exit(EXIT_FAILURE);
    res=pthread_create(&b_thread,NULL,thread_function_read_t,NULL);
    if(res!=0)
        exit(EXIT_FAILURE);
    res=pthread_create(&c_thread,NULL,thread_function_write_o,NULL);
    if(res!=0)
        exit(EXIT_FAILURE);
    res=pthread_create(&d_thread,NULL,thread_function_write_t,NULL);
    if(res!=0)
        exit(EXIT_FAILURE);
    res=pthread_join(a_thread,&thread_result);
    if(res!=0)
        exit(EXIT_FAILURE);
    res=pthread_join(b_thread,&thread_result);
    if(res!=0)
        exit(EXIT_FAILURE);
    res=pthread_join(c_thread,&thread_result);
    if(res!=0)
        exit(EXIT_FAILURE);
    res=pthread_join(d_thread,&thread_result);
    pthread_rwlock_destroy(&rwlock);
    return 0;
}
void *thread_function_read_o(void *arg)
{
    printf("thread read one try to get lock
");
    pthread_rwlock_rdlock(&rwlock);
    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]=='')
        {
            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 two try to get lock
");
    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]=='')
        {
            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
");
    while(!time_to_exit)
    {
        pthread_rwlock_wrlock(&rwlock);
        printf("this is write thread one.
Input some text. Enter 'end' to finish
");
        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)
{
    printf("this is write thread two try to get lock
");
    while(!time_to_exit)
    {
        pthread_rwlock_wrlock(&rwlock);
        printf("this is write thread two.
Input some text. Enter 'end' to finish
");
        fgets(work_area,WORK_SIZE,stdin);
        pthread_rwlock_unlock(&rwlock);
        sleep(20);
    }
    pthread_rwlock_unlock(&rwlock);
    pthread_exit(0);
}