app-dev/cloud-functions-2ndgen-what-are-coldstarts/index.js

/*
 Copyright 2022 Google LLC

 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
 You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
*/

const functions = require("@google-cloud/functions-framework");
const util = require("util");

// note: isWarm is "undefined" until startup() starts executing
// then isWarm becomes a Promise which is never falsey (more below)
var isWarm = startup();

async function startup() {
  console.log("🥶 i'm a cold start");

  // 10 seconds seems to work best for this demo
  await sleep(10000);

  // when setTimeout is finished, have it resume with "I'm ready now"
  // just like any other real world connection
  console.log("I'm ready now");

  // the issue w returning boolean here is that at this point
  // isWarm = Promise { <pending> }
  // so it is always "truthy"
  // returning a string is a much better way to verify the work has been completed
  // and is closer to a real world scenario (e.g. approximating the data you get from an API)
  return "ready";
}

// simulating a long API call or slow network connection
function sleep(ms) {
  return new Promise((resolve) => {
    setTimeout(resolve, ms);
  });
}

functions.http("cold-starts", async (req, res) => {
  // This next line allows you to check whether Promise is pending or is fulfilled
  // if pending, this evaluates to `Promise { <pending> }`
  // if fulfilled, this evaluates to `Promise { 'ready' }`
  // note: isWarm is a Promise, not a string
  var isStatusPending = util.inspect(isWarm).includes("pending");

  // Use stdout to see in Cloud Logging which revision & instanceId is handling the request
  console.log("request received...");

  if (isStatusPending) {
    console.log("I'm still a 🥶 start.");

    // javascript notes:
    // 1) you must use `await isWarm` and not `await isWarm()`
    // because it's a Promise, not a Function.
    // 2) to get the contents "ready" you have to resolve the Promise
    // this next line is the equivalent of calling .then(), so it goes onto "I'm ready now"
    var result = await isWarm;
    console.log("now I'm warmed up 🥰!");
  } else {
    // see note above re javascript
    var result = await isWarm;
    // and you'll see in the logs "I'm awake now" is immediately followed by
    // "I'm a warm instance", where both have the same instanceId
    // All the other "I'm ready now" logs all have different instanceIds
    console.log("🥰 I'm a warm instance.");
  }

  // and either 🥶 or 🥰 our request is completed!
  let message = req.query.message || req.body.message || "Request completed!";
  res.status(200).send(message);
});