boost::asio阻塞等待與非同步等待
阿新 • • 發佈：2019-01-07
阻塞等待：這裡會等待3秒然後才進行輸出。
#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; }
非同步等待：需要一個回撥函式，在等待這個print回撥函式的時候程式會繼續往下執行到io.run為止，3秒過後才會執行回撥函式。如果在3秒內程式還沒有執行到io.run（如加上sleep(5)），那麼5秒後才會執行print，也就是說在執行io.run之前print是不會執行的。
#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; }
// 開始timer的非同步等待時間是1秒，1秒後會執行print回撥函式，在這個函式裡會進行5次遞迴呼叫。由於timer的 // 終止時間是1秒已經到期了所以在遞迴的過程中不會再每秒執行一次的，為了實現每秒輸出的效果我們需要為這個 // timer延遲終止時間，expires_at就是其這個作用。當然expires_at必須在async_wait之前執行，否則是沒有效果的。
#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; }
// 下面是類成員函式回撥的形式
#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;
}