Leveraging Async Hooks to Monitor Event Loop

Utilize async_hooks module to track the asynchronous operations and understand the behavior of the event loop.

const async_hooks = require('async_hooks');
const fs = require('fs');

// Write an async event to the log file
function debug(asyncId, type) {
  fs.writeSync(1, `${type} Async ID: ${asyncId}\n`);
}

// Create Hook
const asyncHook = async_hooks.createHook({
  init(asyncId, type, triggerAsyncId) {
    debug(asyncId, `Init`);
  },
  before(asyncId) {
    debug(asyncId, `Before`);
  },
  after(asyncId) {
    debug(asyncId, `After`);
  },
  destroy(asyncId) {
    debug(asyncId, `Destroy`);
  }
});

// Enable Hook
debug(async_hooks.executionAsyncId(), 'Program Start - Execution Async ID');
asyncHook.enable();

setImmediate(() => {
  console.log('This runs once the event loop is clear.');
});

asyncHook.disable();

This code snippet creates a new async_hooks instance which contains event listeners for various stages of asynchronous operations. It monitors and logs the lifecycle events (init, before, after, destroy) of asynchronous resources. It uses the async_hooks module and fs module for writing logs. As an example, it monitors a `setImmediate` call, which will run after the I/O events.