Function reloadCommand

internal/pgbouncer/config.go:245–271

reloadCommand returns an entrypoint that convinces PgBouncer to reload configuration files. The process will appear as name in `ps` and `top`.

(name string)

// reloadCommand returns an entrypoint that convinces PgBouncer to reload
// configuration files. The process will appear as name in `ps` and `top`.
func reloadCommand(name string) []string {
	// Use a Bash loop to periodically check the mtime of the mounted
	// configuration volume. When it changes, signal PgBouncer and print the
	// observed timestamp.
	//
	// Coreutils `sleep` uses a lot of memory, so the following opens a file
	// descriptor and uses the timeout of the builtin `read` to wait. That same
	// descriptor gets closed and reopened to use the builtin `[ -nt` to check
	// mtimes.
	// - https://unix.stackexchange.com/a/407383
	const script = `
exec {fd}<> <(:||:)
while read -r -t 5 -u "${fd}" ||:; do
  if [[ "${directory}" -nt "/proc/self/fd/${fd}" ]] && pkill -HUP --exact pgbouncer
  then
    exec {fd}>&- && exec {fd}<> <(:||:)
    stat --format='Loaded configuration dated %y' "${directory}"
  fi
done
`

	// Elide the above script from `ps` and `top` by wrapping it in a function
	// and calling that.
	wrapper := `monitor() {` + script + `}; export directory="$1"; export -f monitor; exec -a "$0" bash -ceu monitor`

	return []string{"bash", "-ceu", "--", wrapper, name, configDirectory}
}