ROS ADS integrated to python talk to lgsvl

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background

previously, we had done ADS ros package directly talk with lgsvl. the step further is to trigger ADS ros nodes from scenario python script

a few requirements:

  • for ADS ros should be integrated with each scenario python script, which means, when the python script finished, the ADS ros should exit

  • the ads ros package shell script is independ of python script

execute shell in Python

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subprocess.call("ls -lt", shell=True)
  • to run shell script with a python subprocess 
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proc=subprocess.Popen([""], stdout=subprocess.PIPE)

subprocess.Popen() return the process object

a few helpful commands to debug rosrun:

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ps -aux | grep "roscore"  
ps -aux | grep "rosmaster"
killall -9 roscore 
killall -9 rosmaster

ros1 to python3

there is an real issue, due to the ADS ros package is mostly implemented by ROS1, maintained by the algorithm team. but lgsvl scenario is running with python3. ROS1 matches Python2. so there comes the solution, either to upgrade the ADS ros pakcage to ROS2, or find a way to run ROS1 in python3 env.

conda base env

we had decided to adapt ROS1 in python3 env. as the host machine has conda env, first need to disable conda base. 

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conda config --set auto_activate_base false

as lgsvl scenario is runned with conda python3 env, inside which used subprocess to run ADS ros shell, in which creates a few new gnome-terminals, which are non log-in terminal, and the trick things here: even though disabled auto activate base, and the terminal has no header (base), but when check the python path, it still points to the conda/bin/python, which will fail rosbridge_launch.server, which is a pure ros1 and python2 module.

so need check if conda --version in the ads ros shell script is in current terminal, if does, run conda deactivate, which gives error:

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CommandNotFoundError: Your shell has not been properly configured to use 'conda deactivate'.

it looks there is some mess up, with init conda.sh is in ~/.bashrc, but during the new terminal ceated, it doens’t confgiure all right. which can be fixed :

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conda --version 
if [ $? == 0 ]
then 
    source ~/anaconda3/etc/profile.d/conda.sh
    conda deactivate
fi

in this way, we run lgsvl scenario in python3, as well as can new with python2 terminals to run ads ros nodes from this python3 terminal

ros scripts path is not python path

as we try to separate python scripts from ads ros nodes, so need some global env variable for the ros scripts path.

kill all ros nodes gracefully

we need restart/shutdown the ads ros nodes package at each time when python scenario script start/stop, which has two steps:

  • to shutdown ros nodes, e.g. rosnode kill

  • to close all the gnome-terminals to run the ros nodes

the second step is very tricky, need some understand. A terminal is a file. Like /dev/tty. Files do not have a process id. The process that “owns” the terminal is usually called the controlling process, or more correctly, the process group leader. gnome-terminal runs a single pid, it creates a child process for each and every window and/or tab. and can retrieve these child processes by the command:

$ pgrep -P <pid_of_gnome-terminal>

Many terminals seem to mask themselves as xterm-compatible, which is reported by echo $TERM or echo $COLORTERM. 

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$! is the PID of the last backgrounded process.
kill -0 $PID checks whether it's still running.
$$ is the PID of the current shell.
#! /bin/bash

gnome_pid=`pgrep gnome-terminal`
subpids=`pgrep -P ${gnome_pid}`

if [ ! $1 ]; then
   echo "missing the gnome-terminal pid, exit"
   exit -1
fi

#shutdown the ros nodes 
rosnode kill -a  > /dev/null  2>&1
killall -9 rosmaster > /dev/null  2>&1

#shutdown the terminals where ros nodes hosted
for pid in $subpids
do
        if [[ $pid != $1 ]] ; then
                echo $pid
                kill $pid
        fi
done

tips: the implement has a litle problem when integrate with lgsvl when the simulation time is short, e.g. 1sec, then ros_clear.sh can’t catch the opened gnome-terminals from ros_start.sh.

find the process name using PID

$ ps aux | grep PID
$ ps -p PID -o format         
$ curpid=`ps -p $$ -o ppid=`

the output of ps aux

  • –> in the foreground process group
    s –> is a session leader

summary

so far, we integrated ads ros packages into python, which then talk to lgsvl.

refer

pythn subprocess from Jianshu

understand linux process group

pidof command

which_term

get the info of a PID

get the pid of running terminal