boost::asio阻塞等待与异步等待

阻塞等待：这里会等待3秒然后才进行输出。

#include <iostream>#include <boost/asio.hpp>#include <boost/date_time/posix_time/posix_time.hpp>int main(void){boost::asio::io_service io;boost::asio::deadline_timer timer(io, boost::posix_time::seconds(3));timer.wait();std::cout << "this is blocking wait" << std::endl;system("pause");return 0;}

异步等待：需要一个回调函数，在等待这个print回调函数的时候程序会继续往下执行到io.run为止，3秒过后才会执行回调函数。如果在3秒内程序还没有执行到io.run（如加上sleep(5)），那么5秒后才会执行print，也就是说在执行io.run之前print是不会执行的。

#include <iostream>#include <boost/asio.hpp>#include <boost/date_time/posix_time/posix_time.hpp>void print(const boost::system::error_code & e){std::cout << "hello, world" << std::endl;}int main(void){boost::asio::io_service io;boost::asio::deadline_timer timer(io, boost::posix_time::seconds(3));timer.async_wait(&print);std::cout << "this is asynchronous wait" << std::endl;        // sleep(5);io.run();system("pause");return 0;}

// 开始timer的异步等待时间是1秒，1秒后会执行print回调函数，在这个函数里会进行5次递归调用。由于timer的

// 终止时间是1秒已经到期了所以在递归的过程中不会再每秒执行一次的，为了实现每秒输出的效果我们需要为这个

// timer延迟终止时间，expires_at就是其这个作用。当然expires_at必须在async_wait之前执行，否则是没有效果的。

#include <iostream>#include <boost/asio.hpp>#include <boost/date_time/posix_time/posix_time.hpp>#include <boost/bind.hpp>#include <windows.h>unsigned int start_t, end_t;void print(const boost::system::error_code& e, boost::asio::deadline_timer* timer, int* count){if (*count < 5){std::cout << "count: " << *count << std::endl;end_t = ::GetTickCount();std::cout << "elapse time:" << end_t-start_t << std::endl;++(*count);                //timer->expires_from_now(boost::posix_time::seconds(1));timer->expires_at(timer->expires_at() + boost::posix_time::seconds(1));timer->async_wait(boost::bind(print, boost::asio::placeholders::error, timer, count));}}int main(){int count = 0;boost::asio::io_service io;boost::asio::deadline_timer timer(io, boost::posix_time::seconds(1));timer.async_wait(boost::bind(print, boost::asio::placeholders::error, &timer, &count));start_t = ::GetTickCount();io.run();std::cout << "run end" << std::endl;system("pause");return 0;}

// 下面是类成员函数回调的形式

#include <iostream>#include <boost/asio.hpp>#include <boost/date_time/posix_time/posix_time.hpp>#include <boost/bind.hpp>class Printer{public:Printer(boost::asio::io_service& io): count_(0), timer_(io, boost::posix_time::seconds(1)){timer_.async_wait(boost::bind(&Printer::print, this));}~Printer(){}void print(){if (count_ < 5){std::cout << "count: " << count_ << std::endl;++count_;timer_.expires_from_now(boost::posix_time::seconds(1));timer_.async_wait(boost::bind(&Printer::print, this));}}private:int count_;boost::asio::deadline_timer timer_;};int main(){boost::asio::io_service io;Printer printer(io);io.run();system("pause");return 0;}