Benchmark of calling migemo with several ways from gjs.

gjs-migemo-bench.js

const GLib = imports.gi.GLib;
const Gio = imports.gi.Gio;

function shell_quote(str) {
  return "'" + str + "'";
}

function chomp(str) {
  return str.replace(/[\r\n]+$/, '');
}

function MigemoClient() {
  // Do nothing.
}

MigemoClient.prototype.query = function(query) {
  let [res, out] = GLib.spawn_command_line_sync(
    'sh -c "'
      + ['migemo-client', shell_quote(query), '|', 'nkf', '-w8'].join(' ')
      + '"'
  );
  return res ? chomp(out) : '';
}

function CMigemo() {
  // Do nothing.
}

CMigemo.prototype.query = function(query) {
  let [res, out] = GLib.spawn_command_line_sync(
    ['cmigemo', '-d', '/usr/share/cmigemo/utf-8/migemo-dict', '-w', shell_quote(query)].join(' '));
  return res ? chomp(out) : '';
}

function CMigemoProc() {
  let [res, pid, in_fd, out_fd, err_fd]  = GLib.spawn_async_with_pipes(
    null,
    ['cmigemo', '-d', '/usr/share/cmigemo/utf-8/migemo-dict', '-q', '-n'],
    null, GLib.SpawnFlags.SEARCH_PATH, null);
  if (!res) {
    throw "Failed to spwan cmigemo";
  }
  this.pid = pid;
  this.in_writer = new Gio.DataOutputStream({
    base_stream: new Gio.UnixOutputStream({fd: in_fd})
  });
  this.out_reader = new Gio.DataInputStream({
    base_stream: new Gio.UnixInputStream({fd: out_fd})
  });
}

CMigemoProc.prototype.query = function(query) {
  this.in_writer.put_string(query + '\n', null);
  // XXX: Want to use cancellable.
  let [out, size] = this.out_reader.read_line(null);
  return out;
}


function bench(migemo) {
  let start = new Date().getTime();
  let text = 'aiueo';
  for (let l = 1; l <= text.length; l++) {
    migemo.query(text.slice(0, l));
  }
  for (let l = text.length; l > 0; l--) {
    migemo.query(text.slice(0, l));
  }
  print(migemo.constructor.name + ':' + (new Date().getTime() - start));
}

bench(new MigemoClient());
bench(new CMigemo());
bench(new CMigemoProc());

$ gjs gjs-migemo-bench.js
** (gjs:16292): DEBUG: Command line: gjs gjs-migemo-bench.js
** (gjs:16292): DEBUG: Creating new context to eval console script
MigemoClient:332
CMigemo:1004
CMigemoProc:97