Polling parallel processes using bash
Introduction:
Here is a script I created that polls background processes in bash for one of my projects that not just waits for all the processes to complete using the standard "wait" but also keeps track of the time taken for completion, make sure not to poll the completed ones and finally return the number of failed processes.
So here it is and would really appreciate any feedback!
Idea:
The function takes a list of PID's and a polling interval in seconds. As the interval elapses each time a kill signal is sent to the currently running processes only. A non-zero exit code indicates that process is no longer active - meaning it either completed successfully or failed. By then waiting on that PID the exit code of the process is obtained. This helps in keeping track of the failed count.
#!/bin/sh
STIME=$(date '+%s')
#Poll parallel running processes
#param 1: list of pid's (space delimited)
#param 2: polling interval (secs)
#return value: integer (number of failed processes)
function poll {
local etime=
local elapsed_sec=
local fail=0
local running_pid_list=1ドル
local interval=2ドル
while sleep $interval
do
poll_pid_list=$running_pid_list
if [[ -n $poll_pid_list ]]
then
echo "polling $poll_pid_list"
running_pid_list=
for pid in $poll_pid_list
do
kill -0 $pid 2>/dev/null
if [ $? -ne 0 ]
then
wait $pid
if [[ $? -ne 0 ]]
then
((fail++))
else
etime=$(date '+%s')
elapsed_sec=$((etime - STIME))
echo $pid completed after $elapsed_sec seconds at $etime
fi
else
running_pid_list="$running_pid_list $pid"
fi
done
else
break
fi
done
return $fail
}
#Execute process in parallel as background processes
pid_list=
poll_interval=2
# Process 1
sleep 5 &
pid_list="$pid_list $!"
# Process 2
sleep 10 &
pid_list="$pid_list $!"
poll "$pid_list" $poll_interval
echo "Number of failed processes:$?" In the script above I am running two processes (sleep) in parallel with a set polling interval of 2 sec. In my project I actually write the stats out to a file (not shown above) in a format that i can later read using "awk" and it is a very useful logging mechanism.
Happy Polling!