probe.sh

#!/bin/zsh

read -r -d '' usage <<EOF || true
Usage: $0 [--plot] TOPIC ELF_PUB ELF_SUB

SYNOPSIS

  \$ $0 --plot /topic libpublisher.so libsubscriber.so
  [ a realtime plot of latencies for the given topic pops up ]

DESCRIPTION

This is a wrapper around a bpftrace script for ros2 tracing of communication
latencies. By default this runs bpftrace, and produces its output on stdout.
With --plot, this output is plotted in realtime.

Arguments:

  --plot: if given, plot the latency in realtime

EOF

# comma-separated list of long options. Trailing : means "has required
# argument".
longopts='plot'
Ntrailing_options_required=3

# The parsing code to use getopt comes from
#   /usr/share/doc/util-linux/examples/getopt-example.bash
# I'm not an expert, but this sample makes things work
TEMP=$(getopt -o '' --long $longopts -n "$0" -- "$@")
[ $? -ne 0 ] && {
    echo '' > /dev/stderr
    echo $usage > /dev/stderr
    exit 1;
}
eval set -- "$TEMP"
unset TEMP
# The arguments now appear in a nice canonical order, and they are terminated by
# --

while {true} {
	case "$1" in
	        '--plot')
                        plot=1
                        shift
                        continue
                ;;

                '--')
                        shift
                        break
                ;;

                *)
                        echo 'Internal error in argument parsing' >&2
                        exit 1
                ;;
        esac
}

if (( $#* != Ntrailing_options_required )) {
       echo "Exactly $Ntrailing_options_required non-option arguments are required. Got $#* instead" > /dev/stderr
       echo '' > /dev/stderr
       echo $usage > /dev/stderr
       exit 1
}

# Need the absolute path to work around this bug:
#   https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1063587
topic=$1;        shift;
PUB_option=$1;   shift;
SUB_option=$1;   shift;

PUB=${PUB_option:A};
SUB=${SUB_option:A};

if ! [[ -f "$PUB" ]] {
       echo "Publisher option '$PUB_option' isn't a readable file" > /dev/stderr
       echo '' > /dev/stderr
       echo $usage > /dev/stderr
       exit 1
}
if ! [[ -f "$SUB" ]] {
       echo "Subscriber option '$SUB_option' isn't a readable file" > /dev/stderr
       echo '' > /dev/stderr
       echo $usage > /dev/stderr
       exit 1
}

# I print the legend here. bpftrace doesn't like my overly-long string, and I
# don't want to ask for more bpf memory just to print out the legend
#
# The >>>...<<< replacement replaces all whitespace between those markers with
# _. Needed to post-process the process names coming out of bpftrace
cmd=(sudo zsh -c "echo '## Latency of received messages';
                  echo '# t_ns tid_pub cpu_pub t_latency_take_ns tid_take cpu_take t_latency_sub_ns tid_sub cpu_sub sched from from_prio from_cpu to to_prio to_cpu';
                  bpftrace -q <( <ros2-comm-trace.bt \
                                 | sed 's@{{PUB}}@$PUB@g;
                                        s@{{SUB}}@$SUB@g;'
                               ) $topic \
                 | perl -pe 'BEGIN { $| = 1; }
                             s/tracepoint:sched:sched_//g;
                             s{>>>(.*?)<<<}{\$1 =~ s/\s/_/gr}ge'")

if ((plot)) {
    # The plotter is teed off. The data is always spit out to stdout
    $cmd | \
    tee >( ./plot.sh --stream )
} else {
    $cmd
}