Bash message passing

#
# a single temporary directory with one writer and 50 readers
# the writer:
#    - writes 1000 sequential numbers to files in the directory
#    - then writes 50 "quit{0..49}" files
# each reader:
#    - attempts to read the content of a file in that directory
#    - prints it to stdout
#    - repeats these three steps until nothing remains to be done
#      and it sees a "quit"
#
numReaders=50
numNums=1000

dir="$(mktemp -d)"
IFS=$'\n' # don't split on whitespace, simplifies arrays and loops

# Finds files to process. Ignores temporary files from mktemp and
# quit messages
find_nums()
{
    find "$dir" -mindepth 1 \! \( -name 'quit*' -o -name 'tmp.*' \)
}
# launch readers
for (( i=0; i<numReaders; ++i )); do
    #
    # launch a background sub-shell for each reader
    #
    (
    while true; do
        tmp="$(mktemp --tmpdir="$dir")"
        declare -a nums=( $(find_nums) )
        for num_file in "${nums[@]}"; do
        # renames the file. Thisis an atomic operation and will
        # only succeed for one reader
        mv "$num_file" "$tmp" 2>/dev/null || continue
        num="$(cat "$tmp")"
        # now actually process the file content
        echo "$BASHPID got $num"
        done
        unlink "$tmp"
        sleep 0.1
        if (( ${#nums[@]} > 0 )); then
            continue
        fi
        # no nums, check for quits
        quits=( $(find "$dir" -name 'quit*') )
        if (( ${#quits[@]} == 0 )); then
            continue
        fi
        # got at least one quit. Check again that there are no nums
        # remaining to rule out race condition
        nums=( $(find_nums) )
        if (( ${#nums[@]} > 0 )); then
            continue
        fi
        for quit in "${quits[@]}"; do
        # for quit we don't need the content. unlink is also
        # atomic and will only succeed for one reader
            if unlink "$quit" 2>/dev/null; then
                echo "$BASHPID is done"
                break 2
            fi
        done
    done
    ) &
done
#
# Launch one writer
#
for(( i=0; i < numNums; ++i )); do
    # the content has be written to the file before it gets a name
    # that a reader might find and process. So use a temporary file
    # and then rename it
    tmp="$(mktemp --tmpdir="$dir")"
    printf '%04d\n' "$i" >"$tmp"
    mv "$tmp" "$dir/$i"
done
for(( i=0; i < numReaders; ++i )); do
    touch "$dir/quit$i"
done

echo "Writer finished"
wait # for readers to finish

# don't remove the directory before all readers are done
rmdir "$dir"