nix-bitcoin/examples/qemu-vm/wait-until.sh

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# Wait until $condition is true, retrying every $intervalMs milliseconds.
# Print a '.' character every second as a progress indicator.
waitUntil() {
condition=$1
intervalMs=$2
lastDotTime=$(getTimeMs)
while ! { t0=$(getTimeMs); eval "$condition"; }; do
now=$(getTimeMs)
if ((now - lastDotTime >= 1000)); then
printf .
lastDotTime=$now
fi
toSleep=$((t0 + intervalMs - now))
if ((toSleep > 0)); then
sleep $((toSleep / 1000)).$((toSleep % 1000));
fi
done
}
getTimeMs() { date +%s%3N; }