From 1a2860d3f408beec5173fe59b008f33c4fc6e707 Mon Sep 17 00:00:00 2001
From: Michael Gokhman <michael.gokhman@yahoo.com>
Date: Mon, 8 Apr 2019 08:41:00 +0300
Subject: [PATCH] event-loop-spinner with async_hooks

---
 event-loop-spinner.js | 40 ++++++++++++++++++++++++++++++++++++++++
 index.js              | 15 +++++++++++++++
 2 files changed, 55 insertions(+)
 create mode 100644 event-loop-spinner.js

diff --git a/event-loop-spinner.js b/event-loop-spinner.js
new file mode 100644
index 0000000..391d769
--- /dev/null
+++ b/event-loop-spinner.js
@@ -0,0 +1,40 @@
+const async_hooks = require('async_hooks');
+
+class EventLoopSpinner{
+  constructor() {
+    this.hooksMap = {};
+    this.blockedSince = Date.now();
+
+    const asyncHook = async_hooks.createHook({
+      init: (asyncId, type, triggerAsyncId, resource) => {
+        this.hooksMap[asyncId] = {type};
+      },
+      before: (asyncId) => {
+        if (asyncId === 0) {
+          return;
+        }
+        if (!['TickObject', 'Microtask', 'PROMISE'].includes(this.hooksMap[asyncId].type)) {
+          this.blockedSince = Date.now();
+        }
+      },
+      destroy: (asyncId) => {
+        delete this.hooksMap[asyncId];
+      }
+    });
+    asyncHook.enable();
+  }
+
+  isStarving(thresholdMs = 100) {
+    return Date.now() - this.blockedSince > thresholdMs;
+  }
+
+  async spin() {
+    return new Promise(setImmediate);
+  }
+}
+
+const eventLoopSpinner = new EventLoopSpinner();
+
+module.exports = {
+  eventLoopSpinner,
+}
diff --git a/index.js b/index.js
index c4d1107..16bb531 100644
--- a/index.js
+++ b/index.js
@@ -1,6 +1,8 @@
 const express = require('express');
 const crypto = require('crypto');
 
+const {eventLoopSpinner} = require('./event-loop-spinner');
+
 const PID = process.pid;
 
 function log(msg) {
@@ -74,6 +76,19 @@ app.get('/compute-with-set-immediate', async function computeWSetImmediate(req,
   res.send(hash.digest('hex') + '\n');
 });
 
+app.get('/compute-with-spinner', async function computeWSetImmediate(req, res) {
+  log('computing async with event-loop-spinner!');
+
+  const hash = crypto.createHash('sha256');
+  for (let i = 0; i < 10e6; i++) {
+    hash.update(randomString());
+    if (eventLoopSpinner.isStarving()) {
+      await eventLoopSpinner.spin();
+    }
+  }
+  res.send(hash.digest('hex') + '\n');
+});
+
 app.get('/compute-with-next-tick', async function computeWNextTick (req, res) {
   log('computing async with nextTick!');