fire-and-forgetter

Simple lib to handle fire and forget operations.

Installation

$ npm install fire-and-forgetter --save

The Problem

In NodeJs applications performing fire and forget operations we need a way to wait until all those operations complete in order to perform a graceful application shutdown.

Also, fire and forget operations must have proper error handling in order to avoid 'unhandledRejection'.

Example with Express

const express = require('express')
const someDb = require('some-db');
const app = express();

(async function main() {

    const db = await someDb.connect();
    
    app.post('/', (req, res) => {
        res.send('Got request, now I am processing it in fire and forget mode');
        process(req.body);
    })

    async function process(payload) {
        
        // do some stuff that could take several milliseconds
        // i.e interact with another service, I/O operations, etc..
        // then finally we persist the payload.

        await db.insert(payload);
    }

    const server = app.listen(3000);

    process.on('SIGTERM', async () => {
        try {
            await new Promise(resolve => server.close(resolve));
            // above we have closed the web server, now we are closing db connection
            // however we have may some fire and forget operation still in progress
            // so close the db now won't result in a clear application shutdown
            await db.close();
            process.exit(0);
        } catch (error) {
            process.exit(1);
        }
    });
})().catch(() => {
    process.exit(1);
});

Note: this example is a simplified version of real code, the someDb is a fake package and I haven't execute this code.

The Solution

Fire and forgetter is a tiny library to keep the state of fire and forget operations.

It ensures that a catch is always added to these operations (to avoid any Unhandled Promise Rejections that could lead in memory leaks).

Finally it provides a close method that:

1. resolves when all pending fire and forget operations have been fulfilled or rejected
2. mark the instance as closed so no new fire an forget operations can be executed.

Example with Express

const express = require('express')
const someDb = require('some-db');
const fireAndForgetter = require('fire-and-forgetter').default;
const app = express();

(async function main() {

    const fireAndForget = fireAndForgetter();
    const db = await someDb.connect();
    
    app.post('/', (req, res) => {
        res.send('Got request, now I am processing it in fire and forget mode');
        fireAndForget(() => process(req.body));
    })

    async function process(payload) {
        
        // do some stuff that could take several milliseconds
        // i.e interact with another service, I/O operations, etc..
        // then finally we persist the payload.

        await db.insert(payload);
    }

    const server = app.listen(3000);

    process.on('SIGTERM', async () => {
        try {
            await new Promise(resolve => server.close(resolve));
            // above we have closed the web server, now before closing db connection
            // we are going to close fireAndForget so we wait until all fire and forget
            // operations have been complete and we can safetly close the database connection
            // in order to ensure a good application shutdown
            await fireAndForget.close();
            await db.close();
            process.exit(0);
        } catch (error) {
            process.exit(1);
        }
    });
})().catch(() => {
    process.exit(1);
});

API

Please check tests in order to get more information about the fire and forgetter API.

License

MIT