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

2 Sep 2014


      The following post on Stackoverflow resolved all my questions in this read
and it maybe useful to other people as well:
http://stackoverflow.com/a/25577250

In the example given (for running io service in the background) don't
forget to include boost/thread.cpp and link with corresponding library and
-lrt (runtime lib).

Thanks


On Fri, Aug 29, 2014 at 4:39 PM, Lutz Schneider <
lutz.schneider@alumni.ethz.ch> wrote:
...
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@autistici.org> 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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