示例代码中,在原来boost::asio代码基础上,增加了打印线程id的代码,方便理解多线程执行boost::asio::io_context::run()(或 boost::asio::io_service::run())的特点,同时,在这个示例中,学习boost::asio::io_context::strand的作用,就是,控制执行的顺序,先加入的先执行
#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_context& io)
: strand_(io),
timer1_(io, boost::posix_time::seconds(1)),
timer2_(io, boost::posix_time::seconds(1)),
count_(0)
{
timer1_.async_wait(boost::asio::bind_executor(strand_,
boost::bind(&printer::print1, this)));
timer2_.async_wait(boost::asio::bind_executor(strand_,
boost::bind(&printer::print2, this)));
}
~printer()
{
std::cout << "Final count is " << count_ << std::endl;
}
void print1()
{
if (count_ < 10)
{
std::cout << "threadid = " << boost::this_thread::get_id() << "=> Timer 1: " << count_ << std::endl;
++count_;
timer1_.expires_at(timer1_.expires_at() + boost::posix_time::seconds(1));
timer1_.async_wait(boost::asio::bind_executor(strand_,
boost::bind(&printer::print1, this)));
}
}
void print2()
{
if (count_ < 10)
{
std::cout << "threadid = " << boost::this_thread::get_id() << " => Timer 2: " << count_ << std::endl;
++count_;
timer2_.expires_at(timer2_.expires_at() + boost::posix_time::seconds(1));
timer2_.async_wait(boost::asio::bind_executor(strand_,
boost::bind(&printer::print2, this)));
}
}
private:
boost::asio::io_context::strand strand_;
boost::asio::deadline_timer timer1_;
boost::asio::deadline_timer timer2_;
int count_;
};
int main()
{
boost::asio::io_context io;
printer p(io);
boost::thread t(boost::bind(&boost::asio::io_context::run, &io));
io.run();
t.join();
return 0;
}
实际上,就是超时事件完成Handler可以在两个线程中执行:在线程t或main线程中,如下打印结果: