Outstanding
A task register for facilitating graceful shutdown.
In the world of continuous deployment applications are being started and stopped more frequently than ever. Stopping a process is normally achived by sending a 'SIGINT' or 'SIGTERM' signal. Your node application can listen for this and perform a gracesful shutdown by stopping listeners and closing connections, ensuring that new http requests are rejected, but in-flight ones can complete. But what happens to asynchronous processes that are not part of a request/response workflow, e.g.
In truth there's nothing you can do to completely prevent this scenario. SIGKILL
will kill your application instantly and cannot be listened for, but since most deployment mechanism try SIGTERM
first and wait for a bit before invoking SIGKILL
why not be a good citizen and wait until the asynchronous operations are complete?
This is where outstanding
comes in handy. Outstanding assists with graceful shutdown of node.js applications by providing a way to track asynchronous tasks and block shutdown until they complete or an optional timeout expires.
TL;DR
const Outstanding = const outstanding = timeout: '5s' const signals = 'SIGINT' 'SIGTERM'signals outstanding
Advanced Usage
Wrapping tasks
Sometimes you want to pass a function wrapped with outstanding to an executor.
var wrapped = outstandingasync
Labeling tasks
When you run
or wrap
an asynchronous task, outstanding
keeps track of the function name so you can at least log incomplete tasks on shutdown. If you use anonymous functions or prefer a custom label you can add an extra argument to both these functions, e.g.
outstanding
Getting current tasks
Just call outstanding.list()
. This will return a map of tokens to task details, e.g.
Checking whether outstanding has been shutdown
Use outstanding.isClosed()
. Returns false until outstanding.shutdown(cb)
has been invoked, after which it returns true
Low Level API
The simplest way to use outstanding
is to run or wrap tasks, but you can also use the api synchronously and asynchronously. In this case you need to explicitly use a label.
Asynchronous Usage
outstanding
Synchronous Usage
const token = tasklistif token else console