我的代码是否等同于Boost.Asio教程中给出的代码？

Question

I'm learning Boost.Asio and this is the code I'm talking about: Link to code

The following code I have written appears to be the same and it works: (compile with "-lboost_system" and "-std=c++11")

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

typedef const boost::system::error_code cbse;
int main()
{
    boost::asio::io_service io;

    boost::asio::deadline_timer t(io,boost::posix_time::seconds(1));

    int count=0;

    std::function<void(cbse&)> 
    cb=[&](cbse&)
    {
        if(count<5)
        {
            std::cout<<"foo"<<std::endl;
            count++;
            t.expires_at(t.expires_at()+boost::posix_time::seconds(1));
            t.async_wait(cb);
        }
        else
            std::cout<<"done"<<std::endl;
    };

    t.async_wait(cb);

    std::cout<<"Hello"<<std::endl;

    io.run();

    return 0;
}

Am I missing some important distinction?
Also recursively calling the callback does not seem like a good idea to me intuitively, is it given in the doc just for the sake of explanation?

Answer 1

Am I missing some important distinction?

Your code looks ok, and has about the same behavior as the example code you linked to. The only real difference is that you're accessing t and count from the enclosing scope, rather than using parameters. This is ok in a simple example like this, but can introduce problems for more complex code.

Also recursively calling the callback does not seem like a good idea to me intuitively, is it given in the doc just for the sake of explanation?

Calling async_wait again from the callback is essential to get the desired behavior. Otherwise the callback would be called only once.

Chaining asynchronous callbacks like this can be very useful when done with care, but can quickly lead to difficult to understand/debug code if not.

Answer 2

Your code seems to be ok.

What you do is not recursively calling, because deadlock_timer::async_wait just posts an event and returns immediately. The callback is actually called from loop in ioservice::run .