diff --git a/src/Persistence.js b/src/Persistence.js
index be3acbd4..c39352a9 100644
--- a/src/Persistence.js
+++ b/src/Persistence.js
@@ -2,6 +2,7 @@ import BinaryEncoder from './Binary/Encoder.js'
 import BinaryDecoder from './Binary/Decoder.js'
 import { toBinary, fromBinary } from './MessageHandler/binaryEncode.js'
 import { integrateRemoteStructs } from './MessageHandler/integrateRemoteStructs.js'
+import { createMutualExclude } from './Util/mutualExclude.js'
 
 function getFreshCnf () {
   let buffer = new BinaryEncoder()
@@ -16,6 +17,7 @@ export default class AbstractPersistence {
   constructor (opts) {
     this.opts = opts
     this.ys = new Map()
+    this.mutualExclude = createMutualExclude()
   }
 
   _init (y) {
@@ -45,6 +47,10 @@ export default class AbstractPersistence {
     this.ys.delete(y)
   }
 
+  destroy () {
+    this.ys = null
+  }
+
   /* overwrite */
   saveUpdate (buffer) {
   }
@@ -56,24 +62,28 @@ export default class AbstractPersistence {
   saveStruct (y, struct) {
     let cnf = this.ys.get(y)
     if (cnf !== undefined) {
-      struct._toBinary(cnf.buffer)
-      cnf.len++
+      this.mutualExclude(function () {
+        struct._toBinary(cnf.buffer)
+        cnf.len++
+      })
     }
   }
 
   /* overwrite */
   retrieve (y, model, updates) {
-    y.transact(function () {
-      if (model != null) {
-        fromBinary(y, new BinaryDecoder(new Uint8Array(model)))
-        y._setContentReady()
-      }
-      if (updates != null) {
-        for (let i = 0; i < updates.length; i++) {
-          integrateRemoteStructs(y, new BinaryDecoder(new Uint8Array(updates[i])))
+    this.mutualExclude(function () {
+      y.transact(function () {
+        if (model != null) {
+          fromBinary(y, new BinaryDecoder(new Uint8Array(model)))
           y._setContentReady()
         }
-      }
+        if (updates != null) {
+          for (let i = 0; i < updates.length; i++) {
+            integrateRemoteStructs(y, new BinaryDecoder(new Uint8Array(updates[i])))
+            y._setContentReady()
+          }
+        }
+      })
     })
   }
   /* overwrite */
diff --git a/src/Y.js b/src/Y.js
index ce83e8a4..0ea68b78 100644
--- a/src/Y.js
+++ b/src/Y.js
@@ -22,11 +22,15 @@ import debug from 'debug'
 import Transaction from './Transaction.js'
 
 export default class Y extends NamedEventHandler {
-  constructor (opts, persistence) {
+  constructor (room, opts, persistence) {
     super()
+    this.room = room
+    if (opts != null) {
+      opts.connector.room = room
+    }
     this._contentReady = false
     this._opts = opts
-    this.userID = opts._userID != null ? opts._userID : generateUserID()
+    this.userID = generateUserID()
     this.share = {}
     this.ds = new DeleteStore(this)
     this.os = new OperationStore(this)
@@ -37,9 +41,11 @@ export default class Y extends NamedEventHandler {
     this.connector = null
     this.connected = false
     let initConnection = () => {
-      this.connector = new Y[opts.connector.name](this, opts.connector)
-      this.connected = true
-      this.emit('connectorReady')
+      if (opts != null) {
+        this.connector = new Y[opts.connector.name](this, opts.connector)
+        this.connected = true
+        this.emit('connectorReady')
+      }
     }
     if (persistence != null) {
       this.persistence = persistence
@@ -103,9 +109,6 @@ export default class Y extends NamedEventHandler {
   set _start (start) {
     return null
   }
-  get room () {
-    return this._opts.connector.room
-  }
   define (name, TypeConstructor) {
     let id = new RootID(name, TypeConstructor)
     let type = this.os.get(id)
@@ -138,10 +141,12 @@ export default class Y extends NamedEventHandler {
   destroy () {
     super.destroy()
     this.share = null
-    if (this.connector.destroy != null) {
-      this.connector.destroy()
-    } else {
-      this.connector.disconnect()
+    if (this.connector != null) {
+      if (this.connector.destroy != null) {
+        this.connector.destroy()
+      } else {
+        this.connector.disconnect()
+      }
     }
     if (this.persistence !== null) {
       this.persistence.deinit(this)
diff --git a/tests-lib/helper.js b/tests-lib/helper.js
index 317ab5d9..ebacea27 100644
--- a/tests-lib/helper.js
+++ b/tests-lib/helper.js
@@ -145,7 +145,7 @@ export async function initArrays (t, opts) {
     } else {
       connOpts = Object.assign({ role: 'slave' }, conn)
     }
-    let y = new Y({
+    let y = new Y(connOpts.room, {
       _userID: i, // evil hackery, don't try this at home
       connector: connOpts
     })