void* thread(void * vargp) {
    printf("12.16 homework threadId:  %ld!\n", pthread_self());
    return NULL;
}

int main(int argc, char **argv) {
    if (argc != 2) {
        fprintf(stderr, "usage: %s <n>\n", argv[0]);
        exit(0);
    }
    int n = atoi(argv[1]);
    pthread_t tid[n];
    for (size_t i = 0; i < n; i++) {
        pthread_create(&tid[i], NULL, thread, NULL);
    }
    for (size_t i = 0; i < n; i++) {
        pthread_join(tid[i], NULL); // 等待线程结束
    }
    exit(0);
}

void* thread(void * vargp) {
    sleep(1);
    printf("Hello, world!\n");
    return NULL;
}

int main(int argc, char **argv) {
    pthread_t tid;
    pthread_create(&tid, NULL, thread, NULL);
    pthread_join(tid, NULL);
    exit(0);
}

static int cnt = 0;

void signchld_handler(int sig) {
    // WNOHANG: 如果等待集中的子进程均未终止，则立即返回（返回值为 0）。
    // 默认行为是暂停调用进程，直到子进程终止
    while (waitpid(-1, NULL, WNOHANG) > 0) {
        cnt--;
    }
}

int main(int argc, char **argv) 
{
    int listenfd, connfd;
    char hostname[MAXLINE], port[MAXLINE];
    socklen_t clientlen;
    struct sockaddr_storage clientaddr;


    if (argc != 2) {
        fprintf(stderr, "usage: %s <port>\n", argv[0]);
        exit(1);
    }

    listenfd = Open_listenfd(argv[1]);
    while (1) {
	clientlen = sizeof(clientaddr);
	connfd = Accept(listenfd, (SA *)&clientaddr, &clientlen);
        cnt+=1;
        if (cnt >= 16) {
            //  回收子线程，避免内存泄漏 
            while (waitpid(-1, NULL, WNOHANG) > 0) 
            {
                cnt -= 1;
            }
        }
        Getnameinfo((SA *) &clientaddr, clientlen, hostname, MAXLINE, 
                    port, MAXLINE, 0);
        printf("Accepted connection from (%s, %s)\n", hostname, port);
        if (Fork() == 0) {
            doit(connfd);
            Close(connfd);
            exit(0);
        }
        Close(connfd);
    }
}