Asynchronous shutdown handlers for node.js processes.
npm install shutdown-asyncAsynchronous shutdown handlers for node.js processes.
Consider a database close operation that is an asynchronous function that must be run at shutdown. That shutdown can be invoked by calling process.exit or by pressing ^C.
``javascript`
/**
* Simulate closing a database in an asynchronous function
* returning a promise.
*/
function closeDatabase() {
return new Promise((resolve) => {
console.log('Closing database...');
setTimeout(() => {
console.log('Database closed');
resolve();
}, 1000);
});
}
Now we call that function in our exit handler.
`javascript`
/**
* Close the database on exit. Note: This will not work correctly
* as you cannot call asynchronous functions from an exit handler.
*/
process.on('exit', async () => {
console.log('Shutting down...');
await closeDatabase();
console.log('Shutdown');
});
The output on shutdown will be as follows:
`
Shutting down...
Closing database...
Clearly, this isn't what we want. That is where this module comes in to help. The following is an example of using this module to accomplish the asynchronous database close action.
`javascript
import { addExitHandler, exitGracefully } from '../shutdown-async.js';
function closeDatabase() {
return new Promise((resolve) => {
console.log('Closing database...');
setTimeout(() => {
console.log('Database closed');
resolve();
}, 1000);
});
}
addExitHandler(closeDatabase);
`
When the program is stopped (either by a signal or by calling exitGracefully - discussed below), the output will be as follows:
`
Closing database...
Database closed
The code for both the non-working and working examples is in the examples folder.
Processes must perform asynchronous tasks on exit (stopping a server or closing a database, for example). These asynchronous tasks cannot be performed by handling the 'exit' event as only synchronous operations are permitted.
This module manages both synchronous and asynchronous exit handlers. An asynchronous exit handler is a function returning a promise. Both exceptions thrown by synchronous exit handlers and promises rejected by asynchronous exit handlers are retained.
The exit handlers are run when an exit signal (SIGINT, SIGTERM, SIGHUP, or SIGBREAK) is received or you call exitGracefully. (Calling process.exit instead of calling exitGracefully will not work as the asynchronous exit handlers will not be called.)
Once all exit handlers have been called, the process.exit method is called with the number of errors encountered as the exit status. This will be zero for a successful shutdown or a positive integer for a shutdown where errors occurred.
An additional feature is that a carriage return (\r) is written to stdout on SIGINT so that the echoed ^C character does not offset any console output on shutdown.
`
npm install --save shutdown-async
`javascript
import { addExitHandler } from 'shutdown-async';
addExitHandler(handler);
`
- Adds the specified handler to the queue. The exit handler can be a synchronous function that can throw an exception or an asynchronous function that returns a promise.
`javascript
import { exitGracefully } from 'shutdown-async';
exitGracefully();
`
- Called automatically on SIGINT, SIGTERM, SIGHUP, or SIGBREAK. Runs the exit handlers in the order they were added and then calls process.exit(count) where count is the number of errors (exceptions thrown or promises rejected) encountered while running the exit handlers. Calling this function from your code is optional but not required.
`javascript
import { getExitErrors } from 'shutdown-async';
getExitErrors();
`
- Returns an array of errors encountered while running the exit handlers. Useful for testing. You need not call this function from your code.
The code in the test.js file serves as an example and is the module run by npm test`.
MIT License
Copyright (c) 2022 Frank Hellwig
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