Use push.apply in unlatch.

 % node benchmark/increment/unlatch.js
 signal unlatch 1 x 17,301,870 ops/sec ±0.88% (91 runs sampled)
_signal unlatch 1 x 7,994,106 ops/sec ±2.06% (92 runs sampled)
 signal unlatch 2 x 17,037,813 ops/sec ±2.63% (85 runs sampled)
_signal unlatch 2 x 8,373,249 ops/sec ±0.29% (91 runs sampled)
 signal unlatch 3 x 17,566,441 ops/sec ±2.50% (92 runs sampled)
_signal unlatch 3 x 8,339,125 ops/sec ±0.46% (95 runs sampled)
 signal unlatch 4 x 17,570,954 ops/sec ±2.02% (93 runs sampled)
_signal unlatch 4 x 8,342,331 ops/sec ±0.43% (97 runs sampled)
Fastest is  signal unlatch 4, signal unlatch 3

_signal.js

@@ -71,7 +71,18 @@ Signal.prototype.notify = function () {
             waited.callback.apply(null, arguments)
         }
 
-        this._cancels.splice(this._cancels.indexOf(waits), 1)
+        var i = 0
+        while (i < this._cancels.length) {
+            if (this._cancels[i] === waits) {
+                break
+            }
+            i++
+        }
+        while (i <= this._cancels.length - 1) {
+            this._cancels[i] = this._cancels[i + 1]
+            i++
+        }
+        this._cancels.length--
     }
 }
 

signal.js

@@ -92,7 +92,9 @@ Signal.prototype.notify = function () {
 //
 Signal.prototype.unlatch = function () {
     if (this.open == null) {
-        this.notify.apply(this, this.open = Array.prototype.slice.call(arguments))
+        this.open = []
+        this.open.push.apply(this.open, arguments)
+        this.notify.apply(this, this.open)
     }
 }