async-exit-hook

What is async-exit-hook?

The async-exit-hook npm package allows you to register asynchronous functions that will be called when the Node.js process is exiting. This is useful for cleanup tasks, such as closing database connections, saving state, or other asynchronous operations that need to be completed before the process exits.

What are async-exit-hook's main functionalities?

Registering an asynchronous exit hook

This feature allows you to register an asynchronous function that will be called when the process is exiting. The function can perform any necessary cleanup tasks and must call the provided callback when done.

const exitHook = require('async-exit-hook');

exitHook(async (callback) => {
  console.log('Process is exiting...');
  await new Promise(resolve => setTimeout(resolve, 1000));
  console.log('Cleanup done.');
  callback();
});

// Simulate process exit
die();

Registering multiple exit hooks

You can register multiple asynchronous exit hooks. Each hook will be called in the order they were registered, allowing for complex cleanup sequences.

const exitHook = require('async-exit-hook');

exitHook(async (callback) => {
  console.log('First hook');
  await new Promise(resolve => setTimeout(resolve, 500));
  callback();
});

exitHook(async (callback) => {
  console.log('Second hook');
  await new Promise(resolve => setTimeout(resolve, 500));
  callback();
});

// Simulate process exit
die();

Handling signals

The package can handle various signals (e.g., SIGINT, SIGTERM) and execute the registered hooks when such signals are received, ensuring proper cleanup before the process exits.

const exitHook = require('async-exit-hook');

exitHook(async (callback) => {
  console.log('Received signal, cleaning up...');
  await new Promise(resolve => setTimeout(resolve, 1000));
  console.log('Cleanup done.');
  callback();
});

// Simulate receiving a signal
process.kill(process.pid, 'SIGINT');

Other packages similar to async-exit-hook

exit-hook

The exit-hook package allows you to register synchronous functions to be called when the process exits. Unlike async-exit-hook, it does not support asynchronous operations, making it less suitable for tasks that require asynchronous cleanup.

node-cleanup

The node-cleanup package provides a way to register cleanup handlers that are called when the process exits. It supports both synchronous and asynchronous cleanup functions, similar to async-exit-hook, but offers additional features like handling uncaught exceptions and unhandled promise rejections.

signal-exit

The signal-exit package allows you to execute a callback when the process exits or receives a termination signal. It supports both synchronous and asynchronous callbacks, similar to async-exit-hook, but focuses more on handling various exit signals and conditions.

README

async-exit-hook

Run some code when the process exits

The process.on('exit') event doesn't catch all the ways a process can exit. This module catches:

• process SIGINT, SIGTERM and SIGHUP, SIGBREAK signals
• process beforeExit and exit events
• PM2 clustering process shutdown message (PM2 graceful reload)

Useful for cleaning up. You can also include async handlers, and add custom events to hook and exit on.

Forked and pretty much rewritten from exit-hook.

Install

$ npm install --save async-exit-hook

Usage

Considerations and warning

On process.exit() and asynchronous code

If you use asynchronous exit hooks, DO NOT use process.exit() to exit. The exit event DOES NOT support asynchronous code.

['beforeExit' is not emitted for conditions causing explicit termination, such as process.exit()] (https://nodejs.org/api/process.html#process_event_beforeexit)

Windows and process.kill(signal)

On windows process.kill(signal) immediately kills the process, and does not fire signal events, and as such, cannot be used to gracefully exit. See Clustering and child processes for a workaround when killing child processes. I'm planning to support gracefully exiting with async support on windows soon.

Clustering and child processes

If you use custom clustering / child processes, you can gracefully shutdown your child process by sending a shutdown message (childProc.send('shutdown')).

Example

const exitHook = require('async-exit-hook');

exitHook(() => {
    console.log('exiting');
});

// you can add multiple hooks, even across files
exitHook(() => {
    console.log('exiting 2');
});

// you can add async hooks by accepting a callback
exitHook(callback => {
    setTimeout(() => {
        console.log('exiting 3');
        callback();
    }, 1000);
});

// You can hook uncaught errors with uncaughtExceptionHandler(), consequently adding 
// async support to uncaught errors (normally uncaught errors result in a synchronous exit).
exitHook.uncaughtExceptionHandler(err => {
    console.error(err);
});

// You can hook unhandled rejections with unhandledRejectionHandler()
exitHook.unhandledRejectionHandler(err => {
    console.error(err);
});

// You can add multiple uncaught error handlers
// Add the second parameter (callback) to indicate async hooks
exitHook.uncaughtExceptionHandler((err, callback) => {
    sendErrorToCloudOrWhatever(err) // Returns promise
        .then(() => { 
             console.log('Sent err to cloud'); 
         });
        .catch(sendError => {
             console.error('Error sending to cloud: ', err.stack));
        })
        .then(() => callback);
    });
});

// Add exit hooks for a signal or custom message:

// Custom signal
// Arguments are `signal, exitCode` (SIGBREAK is already handled, this is an example)
exitHook.hookEvent('SIGBREAK', 21);

// process event: `message` with a filter
// filter gets all arguments passed to *handler*: `process.on(message, *handler*)`
// Exits on process event `message` with msg `customShutdownMessage` only
exitHook.hookEvent('message', 0, msg => msg !== 'customShutdownMessage');

// All async hooks will work with uncaught errors when you have specified an uncaughtExceptionHandler
throw new Error('awesome');

//=> // Sync uncaughtExcpetion hooks called and retun
//=> '[Error: awesome]'
//=> // Sync hooks called and retun
//=> 'exiting'
//=> 'exiting 2'
//=> // Async uncaughtException hooks return
//=> 'Sent error to cloud'
//=> // Sync uncaughtException hooks return
//=> 'exiting 3'

License

MIT © Tapani Moilanen
MIT © Sindre Sorhus

Changelog

2.0.1 (2017-08-03)

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