Express.js CPU Hogging Demo - Shows blocking vs non-blocking CPU intensive operations

app.js

const express = require('express');
const app = express();
const port = 3000;

// Quick response route
app.get('/', (req, res) => {
  res.send('Hello World! This route responds quickly.');
});

// CPU intensive route - WARNING: This will block all other requests!
app.get('/cpu-hog', (req, res) => {
  console.log('Starting CPU intensive operation...');

  // Simulate CPU intensive work with a long loop
  let result = 0;
  for (let i = 0; i < 10000000000; i++) {
    result += Math.sqrt(i);
  }

  console.log('CPU intensive operation completed.');
  res.send(`CPU intensive operation completed. Result: ${result}`);
});

// CPU intensive route with cooperative scheduling - allows other requests!
app.get('/cpu-hog2', async (req, res) => {
    req.setTimeout(30);
  console.log('Starting CPU intensive operation with cooperative scheduling...');

  // Simulate CPU intensive work with a long loop, but yield control periodically
  let result = 0;
  const chunkSize = 1000000; // Process 1 million iterations at a time

  for (let i = 0; i < 10000000000; i++) {
    result += Math.sqrt(i);

    // Yield control back to the event loop every chunkSize iterations
    if (i % chunkSize === 0) {
      await new Promise(resolve => setImmediate(resolve));
    }
  }

  console.log('CPU intensive operation with cooperative scheduling completed.');
  res.send(`CPU intensive operation with cooperative scheduling completed. Result: ${result}`);
});

// Another quick route to test blocking
app.get('/test', (req, res) => {
  res.send('This is a test route. If CPU hog is running, this will be blocked!');
});

app.listen(port, () => {
  console.log(`Express app listening at http://localhost:${port}`);
  console.log('Try:');
  console.log('  - GET / (quick response)');
  console.log('  - GET /cpu-hog (CPU intensive - blocks other requests)');
  console.log('  - GET /cpu-hog2 (CPU intensive with cooperative scheduling - allows other requests)');
  console.log('  - GET /test (quick response - will be blocked by /cpu-hog but not by /cpu-hog2)');
});

bun.lock

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    "send/encodeurl": ["[email protected]", "", {}, "sha512-TPJXq8JqFaVYm2CWmPvnP2Iyo4ZSM7/QKcSmuMLDObfpH5fi7RUGmd/rTDf+rut/saiDiQEeVTNgAmJEdAOx0w=="],

    "send/ms": ["[email protected]", "", {}, "sha512-6FlzubTLZG3J2a/NVCAleEhjzq5oxgHyaCU9yYXvcLsvoVaHJq/s5xXI6/XXP6tz7R9xAOtHnSO/tXtF3WRTlA=="],
  }
}

launch.json

{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "Run Express App",
      "type": "node",
      "request": "launch",
      "runtimeExecutable": "bun",
      "program": "${workspaceFolder}/app.js",
      "console": "integratedTerminal",
      "internalConsoleOptions": "openOnSessionStart",
      "skipFiles": [
        "<node_internals>/**"
      ]
    },
    {
      "name": "Debug Express App",
      "type": "node",
      "request": "launch",
      "runtimeExecutable": "bun",
      "program": "${workspaceFolder}/app.js",
      "console": "integratedTerminal",
      "internalConsoleOptions": "openOnSessionStart",
      "skipFiles": [
        "<node_internals>/**"
      ],
      "env": {
        "NODE_ENV": "development"
      }
    },
    {
      "name": "Run with Hot Reload",
      "type": "node",
      "request": "launch",
      "runtimeExecutable": "bun",
      "runtimeArgs": ["--hot"],
      "program": "${workspaceFolder}/app.js",
      "console": "integratedTerminal",
      "internalConsoleOptions": "openOnSessionStart",
      "skipFiles": [
        "<node_internals>/**"
      ],
      "env": {
        "NODE_ENV": "development"
      }
    }
  ]
}

package.json

{
  "name": "express-cpu-hog",
  "version": "1.0.0",
  "description": "Minimal Express app demonstrating CPU intensive operations blocking request handling",
  "main": "app.js",
  "scripts": {
    "start": "bun run app.js",
    "dev": "bun --hot app.js"
  },
  "dependencies": {
    "express": "^4.18.0"
  },
  "keywords": ["express", "cpu", "blocking", "demonstration"],
  "author": "",
  "license": "MIT"
}

tasks.json

{
  "version": "2.0.0",
  "tasks": [
    {
      "label": "Start Express Server",
      "type": "shell",
      "command": "bun",
      "args": ["start"],
      "group": {
        "kind": "build",
        "isDefault": true
      },
      "presentation": {
        "echo": true,
        "reveal": "always",
        "focus": false,
        "panel": "shared"
      },
      "problemMatcher": []
    },
    {
      "label": "Start Dev Server (Hot Reload)",
      "type": "shell",
      "command": "bun",
      "args": ["dev"],
      "group": "build",
      "presentation": {
        "echo": true,
        "reveal": "always",
        "focus": false,
        "panel": "shared"
      },
      "problemMatcher": []
    },
    {
      "label": "Install Dependencies",
      "type": "shell",
      "command": "bun",
      "args": ["install"],
      "group": "build",
      "presentation": {
        "echo": true,
        "reveal": "always",
        "focus": false,
        "panel": "shared"
      },
      "problemMatcher": []
    }
  ]
}