steady_timer没有触发

Question

我需要能够在失效时间后测试函数被调用。在这个失败后，我写了一个小MCE，演示了测试的要点。它不返回处理程序就返回。

取消注释下面的行是否有一个处理程序过期？导致它回显1到控制台，这意味着有一个未到期的处理程序。

按照documentation的

The handler will be called when:

• The timer has expired.
• The timer was cancelled, in which case the handler is passed the error code boost::asio::error::operation_aborted.

所以我觉得我至少应该得到“处理程序”显示在屏幕上时，该行是注释。

担心如果您在sleep_for和yield行之后移动它，仍然有一个处理程序处于活动状态。

为什么我的计时器没有启动？

MCE：

#include <boost/asio.hpp> 
#include <boost/asio/steady_timer.hpp> 
#include <iostream> 
#include <thread> 

void handler(const boost::system::error_code& error) 
{ 
    std::cout << "handler." << std::endl; 
    if (!error) 
    { 
     std::cout << "Timer expired." << std::endl; 
    } 
} 

int main(int argc, char* argv[]) 
{ 
    boost::asio::io_service io_service; 

    // Construct a timer without setting an expiry time. 
    boost::asio::steady_timer timer(io_service); 

    // expire immediately 
    timer.expires_from_now(std::chrono::seconds(0)); 

    // Wait for the timer to expire. 
    timer.async_wait(handler); 

    // is there a handler to expire? 
    // std::cout << "Expiry : " << timer.expires_from_now(std::chrono::seconds(1)) << std::endl; 

    // added to allow the timer to expire 
    std::this_thread::sleep_for(std::chrono::seconds(2)); 
    std::this_thread::yield(); 
} 

Answer 1

问题

您正在使用的wait异步变种，而无需调用io_service.run();

This call is required because operating system-specific functions have to take over control. Remember that it is the I/O service in the I/O service object which implements asynchronous operations based on operating system-specific functions.

解决方案

int main(int argc, char* argv[]) 
{ 
    boost::asio::io_service io_service; 

    // Construct a timer without setting an expiry time. 
    boost::asio::steady_timer timer(io_service); 

    // expire immediately 
    timer.expires_from_now(std::chrono::seconds(0)); 

    // Wait for the timer to expire. 
    timer.async_wait(handler); 

    io_service.run(); 
}