boost timer代码学习笔记

socket连接中需要判断超时 

所以这几天看了看boost中计时器的文档和示例

一共有五个例子 从简单的同步等待到异步调用超时处理

先看第一个例子

// timer1.cpp: 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <iostream>
#include <boost/asio.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>

void print() {
    std::cout << "Hello world" << std::endl;
}

int main()
{
    boost::asio::io_service io;

    boost::asio::deadline_timer t(io,boost::posix_time::seconds(5));
    t.wait();

    print();

    return 0;
}

几行代码 简单的声明计时器 等待五秒后继续执行

但是代码有一个问题就是 等待时间内 流程是卡死的

所以加以改进就是例子2 更改为异步等待

// timer2.cpp: 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <iostream>
#include <boost/asio.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>

void print(const boost::system::error_code&) {
    std::cerr << "Hello world!" << std::endl;
}


int main()
{
    boost::asio::io_service io;
    boost::asio::deadline_timer t(io,boost::posix_time::seconds(5));
    t.async_wait(&print);
    for (int i = 0; i < 3; i++) {
        std::cout << "wait" << std::endl;
    }
    io.run();
    
    return 0;
}

例子3又添加了一个内容

异步等待函数中 再次设置异步等待时间和超时异步调用的回调函数

一共5次  由于传入的是计数count变量的指针 所以计数变量会累加 

当累加到5 则不再继续

代码如下：

// timer3.cpp: 定义控制台应用程序的入口点。
//
#include <iostream>
#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>

void print(const boost::system::error_code& /*e*/,
    boost::asio::deadline_timer* t, int* count)
{
    if (*count < 5)
    {
        std::cout << *count << std::endl;
        ++(*count);

        t->expires_at(t->expires_at() + boost::posix_time::seconds(1));
        t->async_wait(boost::bind(print,
            boost::asio::placeholders::error, t, count));
    }
}

int main()
{
    boost::asio::io_service io;

    int count = 0;
    boost::asio::deadline_timer t(io, boost::posix_time::seconds(1));
    t.async_wait(boost::bind(print,
        boost::asio::placeholders::error, &t, &count));

    io.run();

    std::cout << "Final count is " << count << std::endl;

    return 0;
}

例子4同例子3 不同之处在于 以类的形式封装了超时异步回调函数以及timer

// timer4.cpp: 定义控制台应用程序的入口点。
//
#include <iostream>
#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>

class printer
{
public:
    printer(boost::asio::io_service& io)
        : timer_(io, boost::posix_time::seconds(1)),
        count_(0)
    {
        timer_.async_wait(boost::bind(&printer::print, this));
    }

    ~printer()
    {
        std::cout << "Final count is " << count_ << std::endl;
    }

    void print()
    {
        if (count_ < 5)
        {
            std::cout << count_ << std::endl;
            ++count_;

            timer_.expires_at(timer_.expires_at() + boost::posix_time::seconds(1));
            timer_.async_wait(boost::bind(&printer::print, this));
        }
    }

private:
    boost::asio::deadline_timer timer_;
    int count_;
};

int main()
{
    boost::asio::io_service io;
    printer p(io);
    io.run();

    return 0;
}

例子5开启了两个timer分别在不同线程中运行

基本上阅读没有任何问题

但是实际编写中要深入了解 asio::io_service::strand 和 多线程运行ioser.run（）

这两点需要注意 可以尝试不适用strand_.wrap 

运行代码比对代码运行结果进行理解

代码如下 

#include <iostream>
#include <boost/asio.hpp>
#include <boost/thread/thread.hpp>
#include <boost/bind.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>

class printer
{
public:
    printer(boost::asio::io_service& io)
        : strand_(io),
        timer1_(io, boost::posix_time::seconds(1)),
        timer2_(io, boost::posix_time::seconds(1)),
        count_(0)
    {
        timer1_.async_wait(strand_.wrap(boost::bind(&printer::print1, this)));
        timer2_.async_wait(strand_.wrap(boost::bind(&printer::print2, this)));
    }

    ~printer()
    {
        std::cout << "Final count is " << count_ << std::endl;
    }

    void print1()
    {
        if (count_ < 10)
        {
            std::cout << "Timer 1: " << count_ << std::endl;
            ++count_;

            timer1_.expires_at(timer1_.expires_at() + boost::posix_time::seconds(1));
            timer1_.async_wait(strand_.wrap(boost::bind(&printer::print1, this)));
        }
    }

    void print2()
    {
        if (count_ < 10)
        {
            std::cout << "Timer 2: " << count_ << std::endl;
            ++count_;

            timer2_.expires_at(timer2_.expires_at() + boost::posix_time::seconds(1));
            timer2_.async_wait(strand_.wrap(boost::bind(&printer::print2, this)));
        }
    }

private:
    boost::asio::io_service::strand strand_;
    boost::asio::deadline_timer timer1_;
    boost::asio::deadline_timer timer2_;
    int count_;
};

int main()
{
    boost::asio::io_service io;
    printer p(io);
    boost::thread t(boost::bind(&boost::asio::io_service::run, &io));
    io.run();
    t.join();

    return 0;
}