shutdown-sequence

shutdown-sequence allows composable applications to automatically shut down any services that were created during the application's lifetime. It is intended to be used with IoC / dependency injection, where the application entry point does not know which services will be created and need to be shut down.

Usage

To use, call require('shutdown-sequence').create() in the entry-point application to create a shutdown manager, and export it in your IoC framework. Components that need to run shutdown logic should import this shutdown instance and call add(function) to add a shutdown method. If the shutdown is asynchronous, it can return a promise, and the sequence will wait for the promise to resolve before continuing.

By default, shutdown callbacks are called in the reverse order that they were registered. This way, if component A uses component B, A will not be shutdown until after B is, so that it does not end up using a destroyed dependency.

If your application has further requirements for shutdown ordering, you can call setHeadOrder("A", "B") or setTailOrder("A", "B") to set an ordering of shutdown methods to call before or after all other shutdown methods, respectively. The names correspond to the intrinsic names of the shutdown functions; alternatively, you can explicitly pass a name before the function when calling add().

If any errors are thrown during shutdown (or if a shutdown method returns a failed promise), the shutdown object's error event will be raised, passing the error object and the name of the failed shutdown method. The event will be raised during the shutdown sequence, and subsequent shutdown methods will still run afterwards. (if there are no handlers for the error event, EventEmitter's default behavior will terminate the process, unless in a domain)

The shutdownStarted and shutdownFinished events will also be raised before and after a shutdown, respectively.

Example

app.js

var shutdown = require('shutdown-sequence').create();
 
shutdown.setTailOrder("log");
 
// Pass shutdown to your IoC container

logger.js

module.exports = function(shutdown) {
    shutdown.add("log", function() {  console.log("3"); });
};

database.js

module.exports = function(shutdown) {
    shutdown.add(function() { console.log("2"); });
    shutdown.add(function() { console.log("1"); });
};

Calling shutdown.shutdown() after creating both modules will print 1 2 3.