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

Subject: Re: [Boost-users] problem with asio signal_set and consecutive signals
From: Lutz Schneider (lutz.schneider_at_[hidden])
Date: 2014-08-29 10:39:10

Thanks for the quick response. Now the consecutive signals are handled
correctly and it behaves as I wanted when sending SIGINT signals.
However, and this also holds for my original example (which I only noticed
now), if I don't ever send SIGINT the program never terminates even if I
set the number of loop iterations to a very small number (e.g. 10). If I
stop the program in the debugger after some time it still hasn't exited the
call to io.run().

Is this the expected behavior or am I still doing something wrong. Of
course, if not signal is set I want the program to finish the loop and exit
normally.

Any hint is very much appreciated.

LS

On Wed, Aug 27, 2014 at 11:04 PM, niXman <i.nixman_at_[hidden]> wrote:

> 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
> ___________________________________________________
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