多线程编程：读写锁

#include <stdio.h>
#include <pthread.h>
#include <stdlib.h>
#include <unistd.h>
#define THREADNUM 5
pthread_rwlock_t rwlock;
int data = 0;
void *readers(void *arg){
    while(1) {
        pthread_rwlock_rdlock(&rwlock);
        printf("reader %ld got the lock,---read %d\n", (long) arg, data);

        pthread_rwlock_unlock(&rwlock);

        sleep(1);
        //pthread_exit((void *) 0);
    }
}
void *writers(void *arg){
    while(1) {
        pthread_rwlock_wrlock(&rwlock);
        data++;
        printf("writer %ld got the lock,----write %d\n", (long) arg, data);
        pthread_rwlock_unlock(&rwlock);

        sleep(1);
        //pthread_exit((void *) 0);
    }
}
int main(int argc, char **argv){
    int iRet, i;
    pthread_t writer_id, reader_id;
    pthread_attr_t attr;
    int nreadercount = 1, nwritercount = 1;
    iRet = pthread_rwlock_init(&rwlock, NULL);
    if (iRet) {
        fprintf(stderr, "init lock failed\n");
        return iRet;
    }
    pthread_attr_init(&attr);
    /*pthread_attr_setdetachstate用来设置线程的分离状态
    也就是说一个线程怎么样终止自己，状态设置为PTHREAD_CREATE_DETACHED
    表示以分离状态启动线程*/
    pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
    for (i = 0; i < THREADNUM; i++){
        if (i % 3) {
            pthread_create(&reader_id, &attr, readers, (void *)nreadercount);
            printf("create reader %d\n", nreadercount++);
        } else {
            pthread_create(&writer_id, &attr, writers, (void *)nwritercount);
            printf("create writer %d\n", nwritercount++);
        }
    }
    sleep(5);/*sleep是为了等待另外的线程的执行*/
    return 0;
}