Possible EventEmitter memory leak detected.

mem-leak-warn.js

var http = require('http');

var options = {
	host : 'www.nodejs.org',
	port : 80,
	method : 'HEAD',
	path : '/api/http.html'
};

for( var i = 0 ; i < 10000 ; ++i ) {
	var req = http.request(options, function(res) {
	});
	req.setTimeout(600, function() {
		console.log('timed out');
	});
    req.end();
}

I retract my first two comments. http.request returns a new ClientRequest each time - ClientRequest is an EventEmitter - and hence timeout listeners don't pile up when a connection is reused.

See https://gist.github.com/2973367 for a variant of the test. The leak warning comes up when a new request is created using a socket that has outstanding requests. You can verify this by setting the agent to false in which case the socket has no outstanding requests. This explains why this warning comes up under load with the default agent.

See https://gist.github.com/joyent/node/blob/v0.6.19-release/lib/net.js#L143.