fix bug when tail moves during initial fill

Fix #192

index.js

@@ -117,6 +117,7 @@ class LRUCache {
     this.head = 0
     this.tail = 0
     this.free = new Stack(max)
+    this.initialFill = 1
     this.size = 0
 
     if (typeof dispose === 'function') {
@@ -337,7 +338,7 @@ class LRUCache {
       return this.free.pop()
     }
     // initial fill, just keep writing down the list
-    return this.tail + 1
+    return this.initialFill++
   }
 
   evict () {
@@ -448,6 +449,7 @@ class LRUCache {
     }
     this.head = 0
     this.tail = 0
+    this.initialFill = 1
     this.free.length = 0
     this.calculatedSize = 0
     this.size = 0

test/basic.js

@@ -126,3 +126,14 @@ t.test('peek does not disturb order', t => {
   t.strictSame([...c.values()], [4, 3, 2, 1, 0])
   t.end()
 })
+
+t.test('re-use key before initial fill completed', t => {
+  const c = new LRU({ max: 5 })
+  c.set(0, 0)
+  c.set(1, 1)
+  c.set(2, 2)
+  c.set(1, 2)
+  c.set(3, 3)
+  t.same([...c.entries()], [ [ 3, 3 ], [ 1, 2 ], [ 2, 2 ], [ 0, 0 ] ])
+  t.end()
+})

test/load-check.js

@@ -0,0 +1,53 @@
+process.env.TAP_BAIL = '1'
+const t = require('tap')
+const LRU = require('../')
+const max = 10000
+const cache = new LRU({ max })
+
+const crypto = require('crypto')
+const getVal = () => [
+  crypto.randomBytes(12).toString('hex'),
+  crypto.randomBytes(12).toString('hex'),
+  crypto.randomBytes(12).toString('hex'),
+  crypto.randomBytes(12).toString('hex'),
+]
+
+const seeds = new Array(max * 3)
+// fill up the cache to start
+for (let i = 0; i < max * 3; i++) {
+  const v = getVal()
+  seeds[i] = [v.join(':'), v]
+}
+t.pass('generated seed data')
+
+const verifyCache = () => {
+  // walk down the internal list ensuring that every key is the key to that
+  // index in the keyMap, and the value matches.
+  for (const [k, i] of (cache.map || cache.keyMap).entries()) {
+    const v = cache.valList[i]
+    const key = cache.keyList[i]
+    if (k !== key) {
+      t.equal(k, key, 'key at proper index', { k, i })
+    }
+    if (v.join(':') !== k) {
+      t.equal(k, v.join(':'), 'proper value at index', { v, i })
+    }
+  }
+}
+
+let cycles = 0
+const cycleLength = Math.floor(max / 100)
+while (cycles < max * 5) {
+  const r = Math.floor(Math.random() * seeds.length)
+  const seed = seeds[r]
+  const v = cache.get(seed[0])
+  if (v === undefined) {
+    cache.set(seed[0], seed[1])
+  } else {
+    t.equal(v.join(':'), seed[0], 'correct get ' + cycles, { seed, v })
+  }
+  if (++cycles % cycleLength === 0) {
+    verifyCache()
+    t.pass('cycle check ' + cycles)
+  }
+}