Method ~ThreadPool

practice/threadpool.cpp:28–33

public:
    ThreadPool() {}
    ~ThreadPool() {
        // 释放 Thread 对象占用的堆资源
        for (int i = 0; i < _pool.size(); ++ i) {
            delete _pool[i];
        }
    }

    // 开启线程池
    void startPool(int size)