Move ttlset to the common util folder. Could be used by something else too.

lib/util/ttlset.js

@@ -0,0 +1,108 @@
+var util = require('util')
+
+var EventEmitter = require('eventemitter3').EventEmitter
+
+function TtlItem(value) {
+  this.next = null
+  this.prev = null
+  this.time = null
+  this.value = value
+}
+
+function TtlSet(ttl) {
+  this.head = null
+  this.tail = null
+  this.mapping = Object.create(null)
+  this.ttl = ttl
+  this.timer = null
+}
+
+util.inherits(TtlSet, EventEmitter)
+
+TtlSet.prototype.bump = function(value, time) {
+  var item = this._remove(this.mapping[value]) || this._create(value)
+
+  item.time = time || Date.now()
+  item.prev = this.tail
+
+  this.tail = item
+
+  if (!this.head) {
+    this.head = item
+    this._scheduleCheck()
+  }
+}
+
+TtlSet.prototype.drop = function(value) {
+  this._drop(this.mapping[value])
+}
+
+TtlSet.prototype.stop = function() {
+  clearTimeout(this.timer)
+}
+
+TtlSet.prototype._scheduleCheck = function() {
+  clearTimeout(this.timer)
+  if (this.head) {
+    var delay = Math.max(0, this.ttl - (Date.now() - this.head.time))
+    this.timer = setTimeout(this._check.bind(this), delay)
+  }
+}
+
+TtlSet.prototype._check = function() {
+  var now = Date.now()
+
+  var item
+  while ((item = this.head)) {
+    if (now - item.time > this.ttl) {
+      this._drop(item)
+      this.emit('timeout', item.value)
+    }
+    else {
+      break
+    }
+  }
+
+  this._scheduleCheck()
+}
+
+TtlSet.prototype._create = function(value) {
+  var item = new TtlItem(value)
+  this.mapping[value] = item
+  return item
+}
+
+TtlSet.prototype._drop = function(item) {
+  if (item) {
+    this._remove(item)
+    delete this.mapping[item.value]
+  }
+}
+
+TtlSet.prototype._remove = function(item) {
+  if (!item) {
+    return null
+  }
+
+  if (item.prev) {
+    item.prev.next = item.next
+  }
+
+  if (item.next) {
+    item.next.prev = item.prev
+  }
+
+  if (item === this.head) {
+    this.head = item.next
+  }
+
+  if (item === this.tail) {
+    this.tail = item.prev
+  }
+
+  item.next = item.prev = null
+
+  return item
+}
+
+module.exports = TtlSet