candle

node-candle

A node.js module for weak referenced callbacks with timeouts.

A simple example

var candle = require('candle').candle;

var c = new candle(), id;

id = c.add(function(err, result) { console.log('cb1', err, result); }, 100);
// this will fire at 50ms and output "cb1 null result1.1"
setTimeout(c.resolve.bind(c, id, null, 'result1.1'), 50);
// will fire at 60ms but will not activate the callback since it will have been fred by this time.
setTimeout(c.resolve.bind(c, id, null, 'result1.2'), 60); 

id = c.add(function(err, result) { console.log('cb2', err, result); }, 100);
// this will fire at 150ms, but the callback will have been activated by timeout and output "cb2 timeout undefined"
setTimeout(c.resolve.bind(c, id, null, 'result2'), 150);

// This will fire by timeout and will output "cb3 timeout undefined"
id = c.add(function(err, result) { console.log('cb3', err, result); }, 100);

A network example

The main point of this project comparing to the future and addTimeout is that the candle is more suitable for network applications. Consider the following use case:

Server2 is known that it has unpredictable response time:

socket.on('myrequest', function(payload, id) {
  // dont send anything at all about 'r3'
  if (payload == 'r3') return;

  // send response after 10ms for 'r1', but after 1000ms for 'r2'.
  var timeout = (payload == 'r1') ? 10 : 1000;
  setTimeout(function() {
    socket.emit('myresponse', id, payload + '_response');
  }, timeout);
});

Server1 want to send some requests to the Server2 and wait for at most 100ms.

var candle = require('candle').candle;

var c = new candle();

var start = Date.now();
socket.on('myresponse', function(id, response) {
  c.resolve(id, null, response);
});
var doSmthWithRequest = function(err, request) {
  console.log('got', err, request, 'on', Date.now() - start, 'th ms');
};
socket.emit('myrequest', 'r1', c.add(doSmthWithRequest, 100));
socket.emit('myrequest', 'r2', c.add(doSmthWithRequest, 100));
socket.emit('myrequest', 'r3', c.add(doSmthWithRequest, 100));

This code will likely output the following:

got null r1_response on 13 th ms
got timeout undefined on 102 th ms
got timeout undefined on 102 th ms

Also candle destroys (unreferences) all callback after they have been resolved or timed out to free memory and avoid leaks. As far as the r2_response will be returned after timeout it will be completely ignored.