Re: [Boost-users] problem with asio signal_set and consecutive signals

Subject: Re: [Boost-users] problem with asio signal_set and consecutive signals
From: niXman (i.nixman_at_[hidden])
Date: 2014-08-27 17:04:40

Lutz Schneider 2014-08-28 00:11:
> Hi,
> 
> I have a program and would like to stop it by sending SIGINT for 
> writing
> some data to a file instead of exiting immediately. However, if the 
> user of
> the program sends SIGINT again then the program should quit immediately 
> and
> forget about writing data to a file. For portability reason I would 
> like to
> use boost::asio for this purpose.
> 
> My initial (simplified) approach (see below) did not work. Is this not
> possible or am I missing something?
> 
> handler seems to be called only once (printing out the message) and the
> program always stops when the loop has reached the max iteration 
> number.
> 
> void handler(
>          const boost::system::error_code& error,
>          int signal_number)
> {
>   if (!error)
>     {
>       static bool first = true;
>       if(first){
>         std::cout << " A signal(SIGINT) occurred." << std::endl;
>         // do something like writing data to a file
>         first = false;
>       }else{
>         std::cout << " A signal(SIGINT) occurred, exiting...." << 
> std::endl;
>         exit(0);
>       }
>     }
> }
> 
> int main(){
>   // Construct a signal set registered for process termination.
>   boost::asio::io_service io;
>   boost::asio::signal_set signals(io, SIGINT);
>   // Start an asynchronous wait for one of the signals to occur.
>   signals.async_wait(handler);
>   io.run();
>   size_t i;
>   for(i=0;i<std::numeric_limits<size_t>::max();++i){
>     // time stepping loop, do some computations
>   }
>   std::cout << i << std::endl;
>   return 0;
> }

Hi,

You should set async waiting for next signal immediately in handler, 
like this:
#include <iostream>

#include <boost/bind.hpp>
#include <boost/ref.hpp>
#include <boost/asio.hpp>

void handler(
         boost::asio::signal_set &sset,
         const boost::system::error_code& error,
         int signal_number)
{
         if (!error)
         {
                 sset.async_wait(
                         boost::bind(
                                  handler
                                 ,boost::ref(sset)
                                 ,boost::asio::placeholders::error
                                 
,boost::asio::placeholders::signal_number
                         )
                 );
                 static bool first = true;
                 if(first){
                         std::cout << " A signal(SIGINT) occurred." << 
std::endl;
                         // do something like writing data to a file
                         first = false;
                 }else{
                         std::cout << " A signal(SIGINT) occurred, 
exiting...." << std::endl;
                         exit(0);
                 }
         }
}

int main(){
         // Construct a signal set registered for process termination.
         boost::asio::io_service io;
         boost::asio::signal_set signals(io, SIGINT);
         // Start an asynchronous wait for one of the signals to occur.
         signals.async_wait(
                 boost::bind(
                          handler
                         ,boost::ref(signals)
                         ,boost::asio::placeholders::error
                         ,boost::asio::placeholders::signal_number
                 )
         );

         io.run();
         size_t i;
         for(i=0;i<std::numeric_limits<size_t>::max();++i){
                 // time stepping loop, do some computations
         }
         std::cout << i << std::endl;
         return 0;
}

(http://pastebin.com/RuxQ5ARw)

-- 
Regards, niXman
___________________________________________________
Dual-target(32 & 64-bit) MinGW-W64 compilers for 32 and 64-bit Windows:
http://sourceforge.net/projects/mingw-w64/
___________________________________________________
Another online IDE: http://liveworkspace.org/