[ros-users] ROS nodes & SIGINT handler

[Gautier Dumonteil]

  Hi users,

In our reseach project, we would like to be able to record bags 
"automatically" (e.g recording when our UAV is flying).
So, I'm trying to write a simple node (/recorder_interface/) with two 
services "start_record" and "stop_record", where "start_record" callback 
launch the rosbag::recorder::run() in a child process using fork(). The 
"stop_record" callback just sends the SIGINT signal to recorder PID to 
stop recording ... but nothing happen. It seems that the ROS node forked 
doesn't handle SIGINT signals.

Also, when checking available nodes with "rosnode list", I've only the 
/recorder_interface/ node. I should have also something like 
"record_1283279499007996727", which is the rosbag record node.

I'm wondering if a node can launch others nodes??

Here, the console output and code:

[ INFO] [1283279481.648585599]: Recorder_interface spinning: ready to 
record.
[ INFO] [1283279499.006083281]: Request to record topics: test
[ INFO] [1283279499.007996722]: Child: pid = 10497

[ INFO] [1283279499.008979878]: Subscribing to /fake_alti
[ INFO] [1283279499.009749320]: Recording to test_2010-08-31-14-31-39.bag.

#include <signal.h>
#include "ros/ros.h"
#include "recorder_interface/rec_interface.h"
#include "rosbag/recorder.h"
#include "rosbag/exceptions.h"

bool  recording;
int   recorder_exit_code;
pid_t rosbag_pid;

void rosbagRecord (rosbag::RecorderOptions opts)
{
     char ** argv = NULL;
     int argc=0;
     ros::init(argc, argv, "record", ros::init_options::AnonymousName);

     // **** Run the recorder
     rosbag::Recorder recorder(opts);
     recorder_exit_code = recorder.run();
     ROS_INFO("recorder_exit_code: %d\n",recorder_exit_code);
}

bool startRec(recorder_interface::rec_interface::Request &req,
                   recorder_interface::rec_interface::Response &res)
{
     if(!recording)
     {
         recording=true;
         ROS_INFO("Request to record topics: %s", req.topics.c_str ());

         // **** Fill rosbag options
         rosbag::RecorderOptions opts;
         opts.record_all = false;
         opts.quiet = true;
         opts.prefix = req.prefix;
         opts.append_date = true;
         opts.topics.push_back("/fake_alti");

         rosbag_pid = fork();
         if(rosbag_pid == -1)
         {
             // **** ouch, fork() failed
             perror("fork");
             exit(-1);
         }
         else if(rosbag_pid == 0)
         {
             // **** child
             ROS_INFO("Child: pid = %d\n", (int)getpid());
             rosbagRecord(opts);
             exit(-1);
         }
     }
     else
     {
         ROS_WARN("Already recording!");
     }
    return true;
}


bool stopRec(recorder_interface::rec_interface::Request &req,
                   recorder_interface::rec_interface::Response &res)
{
    if(recording)
     {
         int err = kill(rosbag_pid, SIGINT);
         ROS_INFO("err = %d\n",err);
         if(err==0)
         {
             res.ans=recorder_exit_code;
             recording=false;
         }
     }
     else
     {
         ROS_WARN("Not recording!");
     }
    return true;
}

int main(int argc, char **argv)
{
   recording=false;

   ros::init(argc, argv, "recorder_interface");
   ros::NodeHandle n;

   ros::ServiceServer serviceStart,serviceStop;
   serviceStart = n.advertiseService("start_record", startRec);
   serviceStop = n.advertiseService("stop_record", stopRec);
   ROS_INFO("Recorder_interface spinning: ready to record.");
   ros::spin();
   return 0;
}


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