io_service相当于注册异步回调的一个上下文环境，而run相当于处理异步io的上下文（通常是一个线程）。

单io_service，多线程run，相当于多个线程同时来处理注册在一个io_service上的回调：

//sio_mth.cpp
#include <boost/asio.hpp>
#include <boost/date_time/posix_time/posix_time_types.hpp>
#include <iostream>
#include <chrono>
#include <thread>
#include <functional>
using namespace boost::asio;
using namespace std;thread_local int t_id = 0;
unsigned long getTimestamp()
{return std::chrono::system_clock::now().time_since_epoch().count()/std::chrono::system_clock::period::den;
}void timer_handler(int timerID, const boost::system::error_code& err)
{if (err){cout << getTimestamp() << " Timer cancel" << endl;return;}cout << getTimestamp() <<" t_id:" << t_id << " timerID:" << timerID << " " << " Time