monitoring active libuv handles with node.js

curl-shell.txt

$ curl localhost:8080/ &
[1] 70338
$ curl localhost:8080/ &
[2] 70347
$ curl localhost:8080/ &
[3] 70356
$ curl localhost:8080/ &
[4] 70365
$ curl localhost:8080/ &
[5] 70374
$ curl localhost:8080/ &
[6] 70383
$ hello world!
[1]    70338 done       curl localhost:8080/
$ hello world!
[2]    70347 done       curl localhost:8080/
$ hello world!
[3]    70356 done       curl localhost:8080/
$ hello world!
[4]    70365 done       curl localhost:8080/
$ hello world!
[5]  - 70374 done       curl localhost:8080/
$ hello world!
[6]  + 70383 done       curl localhost:8080/
$

server-shell.txt

$ node /tmp/event-loop-monitoring.js
server listening on port 8080...
Number of active handles: 3
Active handles: { Server: 1, WriteStream: 2 }
Number of active handles: 10
Active handles: { Server: 1, WriteStream: 2, Socket: 6, Timer: 1 }
Number of active handles: 3
Active handles: { Server: 1, WriteStream: 2 }

server.js

const http = require('http');
const PORT = 8080;

const server = http.createServer(function onReq(req, res) {	
	setTimeout(function() {
		res.end('hello world!');
	}, 10000);
});

server.listen(PORT, function onListen() {
	console.log(`server listening on port ${PORT}...`);
});

process.on('SIGUSR1', function onSignal() {
	const activeHandles = process._getActiveHandles();
	const activeHandlesByConstructor = {};

	console.log('Number of active handles:', activeHandles.length);

	activeHandles.forEach(function(activeHandle) {
		if (activeHandlesByConstructor[activeHandle.constructor.name] !== undefined)
			++activeHandlesByConstructor[activeHandle.constructor.name];
		else
			activeHandlesByConstructor[activeHandle.constructor.name] = 1;
	});
	console.log('Active handles:', activeHandlesByConstructor);
});