fix(memo): use lru-cache for better mem management (#75)

Fixes: #74

Author: zkat

lib/memoization.js

@@ -1,11 +1,27 @@
 'use strict'
 
-let MEMOIZED = {}
+const LRU = require('lru-cache')
+
+const MAX_SIZE = 50 * 1024 * 1024 // 50MB
+const MAX_AGE = 3 * 60 * 1000
+
+let MEMOIZED
+clearMemoized()
 
 module.exports.clearMemoized = clearMemoized
 function clearMemoized () {
   var old = MEMOIZED
-  MEMOIZED = {}
+  MEMOIZED = new LRU({
+    max: MAX_SIZE,
+    maxAge: MAX_AGE,
+    length: (entry, key) => {
+      if (key.startsWith('key:')) {
+        return entry.data.length
+      } else if (key.startsWith('digest:')) {
+        return entry.length
+      }
+    }
+  })
   return old
 }
 

package.json

@@ -52,6 +52,7 @@
     "chownr": "^1.0.1",
     "glob": "^7.1.1",
     "graceful-fs": "^4.1.10",
+    "lru-cache": "^4.0.2",
     "mississippi": "^1.2.0",
     "mkdirp": "^0.5.1",
     "promise-inflight": "^1.0.1",