The doubly linked list implementation was revealed to be buggy by simple unit tests. Fixed.

lib/util/ttlset.js

@@ -28,7 +28,10 @@ TtlSet.prototype.bump = function(value, time) {
 
   this.tail = item
 
-  if (!this.head) {
+  if (item.prev) {
+    item.prev.next = item
+  }
+  else {
     this.head = item
     this._scheduleCheck()
   }

test/util/ttlset.js

@@ -0,0 +1,100 @@
+var chai = require('chai')
+var expect = chai.expect
+
+var TtlSet = require('../../lib/util/ttlset')
+
+describe('TtlSet', function() {
+
+  describe('bump', function() {
+
+    it('should create an item for the value if none exists', function(done) {
+      var ttlset = new TtlSet(5000)
+      ttlset.bump(5)
+      expect(ttlset.head).to.equal(ttlset.tail)
+      expect(ttlset.head.value).to.equal(5)
+      done()
+    })
+
+    it('should make the item the new tail', function(done) {
+      var ttlset = new TtlSet(5000)
+      ttlset.bump(5)
+      expect(ttlset.tail.value).to.equal(5)
+      ttlset.bump(6)
+      expect(ttlset.tail.value).to.equal(6)
+      done()
+    })
+
+    it('should set head if none exists', function(done) {
+      var ttlset = new TtlSet(5000)
+      expect(ttlset.head).to.be.null
+      ttlset.bump(5)
+      expect(ttlset.head.value).to.equal(5)
+      ttlset.bump(6)
+      expect(ttlset.head.value).to.equal(5)
+      done()
+    })
+
+    it('should take old item out and make it the tail', function(done) {
+      var ttlset = new TtlSet(5000)
+      ttlset.bump(1)
+      expect(ttlset.head.value).to.equal(1)
+      expect(ttlset.tail.value).to.equal(1)
+      expect(ttlset.head.next).to.be.null
+      expect(ttlset.head.prev).to.be.null
+      expect(ttlset.tail.next).to.be.null
+      expect(ttlset.tail.prev).to.be.null
+      ttlset.bump(2)
+      expect(ttlset.head.value).to.equal(1)
+      expect(ttlset.tail.value).to.equal(2)
+      expect(ttlset.head.next).to.equal(ttlset.tail)
+      expect(ttlset.head.prev).to.be.null
+      expect(ttlset.tail.next).to.be.null
+      expect(ttlset.tail.prev).to.equal(ttlset.head)
+      ttlset.bump(1)
+      expect(ttlset.head.value).to.equal(2)
+      expect(ttlset.tail.value).to.equal(1)
+      expect(ttlset.head.next).to.equal(ttlset.tail)
+      expect(ttlset.head.prev).to.be.null
+      expect(ttlset.tail.next).to.be.null
+      expect(ttlset.tail.prev).to.equal(ttlset.head)
+      ttlset.bump(1)
+      expect(ttlset.head.value).to.equal(2)
+      expect(ttlset.tail.value).to.equal(1)
+      expect(ttlset.head.next).to.equal(ttlset.tail)
+      expect(ttlset.head.prev).to.be.null
+      expect(ttlset.tail.next).to.be.null
+      expect(ttlset.tail.prev).to.equal(ttlset.head)
+      done()
+    })
+
+  })
+
+  describe('drop', function() {
+
+    it('should silently ignore unknown values', function(done) {
+      var ttlset = new TtlSet(5000)
+      ttlset.drop(5)
+      done()
+    })
+
+    it('should remove the value from the set', function(done) {
+      var ttlset = new TtlSet(5000)
+      ttlset.bump(5)
+      ttlset.drop(5)
+      expect(ttlset.tail).to.be.null
+      expect(ttlset.head).to.be.null
+      ttlset.bump(1)
+      ttlset.bump(2)
+      ttlset.drop(1)
+      expect(ttlset.tail).to.equal(ttlset.head)
+      expect(ttlset.tail.value).to.equal(2)
+      ttlset.bump(3)
+      ttlset.drop(3)
+      expect(ttlset.tail).to.equal(ttlset.head)
+      expect(ttlset.tail.value).to.equal(2)
+      done()
+    })
+
+  })
+
+})