node/lib/internal/inspector_async_hook.js

'use strict';

const { createHook } = require('async_hooks');
const inspector = process.binding('inspector');
const config = process.binding('config');

if (!inspector || !inspector.asyncTaskScheduled) {
  exports.setup = function() {};
  return;
}

const hook = createHook({
  init(asyncId, type, triggerAsyncId, resource) {
    // It's difficult to tell which tasks will be recurring and which won't,
    // therefore we mark all tasks as recurring. Based on the discussion
    // in https://github.com/nodejs/node/pull/13870#discussion_r124515293,
    // this should be fine as long as we call asyncTaskCanceled() too.
    const recurring = true;
    inspector.asyncTaskScheduled(type, asyncId, recurring);
  },

  before(asyncId) {
    inspector.asyncTaskStarted(asyncId);
  },

  after(asyncId) {
    inspector.asyncTaskFinished(asyncId);
  },

  destroy(asyncId) {
    inspector.asyncTaskCanceled(asyncId);
  },
});

function enable() {
  if (config.bits < 64) {
    // V8 Inspector stores task ids as (void*) pointers.
    // async_hooks store ids as 64bit numbers.
    // As a result, we cannot reliably translate async_hook ids to V8 async_task
    // ids on 32bit platforms.
    process.emitWarning(
      'Warning: Async stack traces in debugger are not available ' +
      `on ${config.bits}bit platforms. The feature is disabled.`,
      {
        code: 'INSPECTOR_ASYNC_STACK_TRACES_NOT_AVAILABLE',
      });
  } else {
    hook.enable();
  }
}

function disable() {
  hook.disable();
}

exports.setup = function() {
  inspector.registerAsyncHook(enable, disable);

  if (inspector.isEnabled()) {
    // If the inspector was already enabled via --inspect or --inspect-brk,
    // the we need to enable the async hook immediately at startup.
    enable();
  }
};