1var wrappy = require('wrappy') 2var reqs = Object.create(null) 3var once = require('once') 4 5module.exports = wrappy(inflight) 6 7function inflight (key, cb) { 8 if (reqs[key]) { 9 reqs[key].push(cb) 10 return null 11 } else { 12 reqs[key] = [cb] 13 return makeres(key) 14 } 15} 16 17function makeres (key) { 18 return once(function RES () { 19 var cbs = reqs[key] 20 var len = cbs.length 21 var args = slice(arguments) 22 23 // XXX It's somewhat ambiguous whether a new callback added in this 24 // pass should be queued for later execution if something in the 25 // list of callbacks throws, or if it should just be discarded. 26 // However, it's such an edge case that it hardly matters, and either 27 // choice is likely as surprising as the other. 28 // As it happens, we do go ahead and schedule it for later execution. 29 try { 30 for (var i = 0; i < len; i++) { 31 cbs[i].apply(null, args) 32 } 33 } finally { 34 if (cbs.length > len) { 35 // added more in the interim. 36 // de-zalgo, just in case, but don't call again. 37 cbs.splice(0, len) 38 process.nextTick(function () { 39 RES.apply(null, args) 40 }) 41 } else { 42 delete reqs[key] 43 } 44 } 45 }) 46} 47 48function slice (args) { 49 var length = args.length 50 var array = [] 51 52 for (var i = 0; i < length; i++) array[i] = args[i] 53 return array 54} 55