c++ break while

#include <iostream>
#include <vector>
#include <pthread.h>
#include "destory_free_while.h"
using namespace std;

Worker::Worker() {
    shutdown = false;
    num_thread = 10;
}
void Worker::start() {
    tids.resize(num_thread);
    for (int i = 0; i <num_thread ; ++i) { 
        if (pthread_create(&tids[i], NULL, sleeping, this) == 0) {
            cout << "thread start complete" << endl;
        }
    }
}

Worker::~Worker() {
    cout << "begin destory instance" << endl;
    shutdown = true;
    for(unsigned int i=0; i<tids.size(); i++) {
        pthread_join(tids[i], NULL);
    }
}


void* Worker::sleeping(void* arg) {
    Worker* work = (Worker*)arg;  
    while(true) {
        cout << "." << flush;
        sleep(1);
        if(work->shutdown) {
            cout << " destory instance , thread quit" << endl;
            break;
        }

    }
}

/* vim: set ts=4 sw=4 sts=4 tw=100 */

#ifndef DESTORY_FREE_WHILE_H
#define DESTORY_FREE_WHILE_H
#include <vector>
#include <pthread.h>
class Worker {
public:
    Worker();
    ~Worker();
    void start();
public:
    static void* sleeping(void* arg);
public:
    std::vector<pthread_t> tids;
    int num_thread;
    bool shutdown; 
};

#endif  // DESTORY_FREE_WHILE_H

#include <iostream>
#include "destory_free_while.h"
using namespace std;

int main() {
    Worker worker;
    worker.start();
    sleep(20);
    cout << "program exit" << endl;
}