[ros-users] ROS nodes & SIGINT handler

[Gautier Dumonteil]

  It was exactly the problem I had (not respond to SIGINT) but 
fork()/exec() seems to work in my case.
But I'll take a look at rxbag's Recorder class.

Thx
Gautier

Le 31/08/2010 19:53, Kaijen Hsiao a écrit :
> I would recommend against using fork()/exec() to run "rosbag record",
> actually--I tried to do so myself not long ago, and found that the
> forked process wouldn't respond to SIGINT, and so I couldn't close any
> of the bagfiles being recorded.  Although maybe you'll have better
> luck (or maybe Tim knows of a trick to make that work--I'm certainly
> no expert at using fork/exec).
>
> rxbag's Recorder class, on the other hand, was fairly easy to extend
> for my needs.
>
> -Kaijen
>
> On Tue, Aug 31, 2010 at 3:39 PM, Tim Field<tfield at willowgarage.com>  wrote:
>> Hi Gautier,
>> One option is rxbag's Recorder class,
>> i.e. https://code.ros.org/svn/ros/stacks/ros/tags/cturtle/tools/rxbag/src/rxbag/recorder.py.
>> Here's some code to get you started:
>>
>> import roslib; roslib.load_manifest('rxbag')
>> from rxbag.recorder import Recorder
>> r = Recorder('altimeter.bag', topics=['/fake_alti'])
>> r.start()
>> r.pause()
>> r.unpause()
>> r.stop()
>>
>> If that's too slow to record your data (ROS message serialization is slow in
>> Python), I'd follow Josh's suggestion and fork()/exec() a process to run
>> "rosbag record".
>> For Diamondback, rosbag will have a ROS API for recording and playback.
>> Tim
>> On Tue, Aug 31, 2010 at 12:06 PM, Gautier Dumonteil
>> <gautier.dumonteil at gmail.com>  wrote:
>>> 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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>>
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