How do I wait for all child processes but one to finish executing

Question

I am starting a number of processes in the background of the scrip that I'm writing. I want to wait for some of them to finish before the end of each iteration of a for loop, but there is one process that I need to leave running and end separately. What I'm doing right now doesn't work as I seem to run out of memory, and more and more processes are sacrificed, including the script that I'm running. What I currently have is:

loadAvg &
pid=$!
echo "LA pid $pid"
for (( j=0; j < $units_to_fill; j=$((j+1)) )); do
    #Print all files in dir | shuffle file names | delete 1st 1024 files found
    if [ $from_zero -ne 1 ];then
        stat -c %n * | sort -rz | awk -v n=0 '/file_[0-9]*_[abcd].bin/ { if( ++n <= 1024) {print $1 ; }}' | xargs -r rm -f
    fi
    echo "Creating file $j"
    pids=$(writeFile "file_${j}.bin" $src_file $block_size $block_count "${wd}/${dd_log_file}") #Writes a file of (dd) block size 1MB, with 1024 blocks
    for job in `jobs -p`; do
        if [[ $job -ne $pid ]]; then
            echo "Waiting for $job"             
            wait $job
        fi
    done
done
kill $pid

The function writeFile spawns a number of child processes, and I can't guarantee the order that they'll exit in, as I was previously doing wait $! in place of the

for job in `jobs -p`

I can capture the pids of the child processes that are spawned in the function, and they are currently being returned in a format that's essentially pid1 pid2 pid3 ..., but running wait $pids doesn't work as some of the processes finish before that line is reached, so wait errors out.

Note: I'm running on an embedded system with busybox linux installed, and as such it's been quite cut down and a lot of standard functions are unavailable.

Answer 1

The wait command can be given multiple arguments, and it will wait for all those processes to exit. So put all the PIDs you want to wait for into an array in the loop, and then use:

wait ${pids[@]}

after the loop.