mutexが必要？？

mutex.js

'use strict';
const { Mutex } = require( 'await-semaphore' );

/**
 * スリープ
 */
const _sleep = ( waitSec ) => {
  return new Promise( function ( resolve ) {
    setTimeout( function () { resolve(); }, waitSec );
  } );
};
/**
 * ダミー関数
 * @param {*} val 
 */
const f = async ( val ) => {
  await _sleep( Math.random() * 1000 );
  return val;
};

/**
 * main
 */
const main = async () => {
  // 戻り値格納配列
  const retDatas = [];
  // 処理データダミー
  const dummyDatas = [];
  const mutex = new Mutex();
  for ( let i = 0; i <= 999999; ++i ) {
    dummyDatas.push( i );
  }
  // 測定開始
  var start = new Date();

  await Promise.all(
    dummyDatas.map( async ( val ) => {
      const ret = await f( val );
      // 共有変数を操作するのに排他制御が必要なのではないか？
      mutex.use( async () => {
        retDatas.push( ret );
      } );
    } )
  );

  /*
  for ( const val of dummyDatas ) {
    const ret = await f( val );
    retDatas.push( ret );
  }
  */
  //結果
  console.log( retDatas );
  var end = new Date() - start;
  console.info( 'Execution time: %dms', end );
};

// main
// 即時実行関数を定義
( async () => {
  try {
    await main();
  } catch ( e ) {

  }
} )();