[SOLVED] Run parallel for loop to run k6 in posix

Issue

I need to run a parallel for loop in posix shell (not bash). But it is currently not executing in docker and skipping that statement on adding & to the for loop.

Reference question with details: Shell script not running as bash using Dockerfile

Code snippet from reference question:

if [ -z "$GWC_PC_ID" ]
then
   ENV_NAME=$ENV_NAME RUN_OPTIONS=$SCENARIO_NAME-$ENV_NAME$OPTIONS_VARIANT k6 run $K6_RUN_OPTIONS ''$SCENARIO/index.js''
else
   for pcId in $(printf '%s' "$GWC_PC_ID" | tr , ' ');
   do
      ENV_NAME=$ENV_NAME RUN_OPTIONS=$SCENARIO_NAME-$ENV_NAME$OPTIONS_VARIANT GWC_PC_ID=$pcId k6 run $K6_RUN_OPTIONS ''$SCENARIO/index.js'' &
   done
fi

Here if I give empty input, it runs fine but for non-empty input, it does not execute statement inside for loop. Note that if I remove & then it executes the statement inside for loop but I need to run those statements parallely.

Solution

The issue was because it was not waiting for process to finish and exiting before it can execute the forked threads. For waiting for the forked threads, I needed an array of process ids. Since array is not supported I installed bash in my docker.

To do that I modified Dockerfile as follows:

FROM grafana/k6:0.40.0
COPY ./src/lib /lib
COPY ./src/scenarios /scenarios
COPY ./src/k6-run-all.sh /k6-run-all.sh
WORKDIR /
ENTRYPOINT []
USER root
RUN apk add --no-cache bash
CMD ["bash", "-c", "./k6-run-all.sh"]

Additionally I added the following to my script to wait for processes to finish:

if [ -z "$GWC_PC_ID" ]
then
   ENV_NAME=$ENV_NAME RUN_OPTIONS=$SCENARIO_NAME-$ENV_NAME$OPTIONS_VARIANT k6 run $K6_RUN_OPTIONS ''$SCENARIO/index.js''
else
   i=0
   for pcId in $(printf '%s' "$GWC_PC_ID" | tr , ' ');
   do
      ENV_NAME=$ENV_NAME RUN_OPTIONS=$SCENARIO_NAME-$ENV_NAME$OPTIONS_VARIANT GWC_PC_ID=$pcId k6 run $K6_RUN_OPTIONS ''$SCENARIO/index.js'' &
      pids[${i}]=$!
      ((i=i+1))
   done
fi

# wait for all pids
for pid in ${pids[*]}; do
    echo "Waiting for" $pid
    wait $pid
done

Also added #!/bin/bash to the top of this script file.

Answered By - Sonali Agrawal

Answer Checked By - Willingham (WPSolving Volunteer)