diff --git a/lib/logic/croupier.dart b/lib/logic/croupier.dart
index 5cb2eb4..eec18d6 100644
--- a/lib/logic/croupier.dart
+++ b/lib/logic/croupier.dart
@@ -2,11 +2,13 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-import 'game/game.dart'
-    show Game, GameType, GameStartData, stringToGameType, gameTypeToString;
+import 'dart:async';
+
+import '../src/syncbase/settings_manager.dart' show SettingsManager;
 import 'create_game.dart' as cg;
 import 'croupier_settings.dart' show CroupierSettings;
-import '../src/syncbase/settings_manager.dart' show SettingsManager;
+import 'game/game.dart'
+    show Game, GameType, GameStartData, stringToGameType, gameTypeToString;
 
 enum CroupierState {
   Welcome,
@@ -30,6 +32,10 @@
   Game game; // null until chosen
   NoArgCb informUICb;
 
+  // Futures to use in order to cancel scans and advertisements.
+  Future _scanFuture;
+  Future _advertiseFuture;
+
   Croupier() {
     state = CroupierState.Welcome;
     settings_everyone = new Map<int, CroupierSettings>();
@@ -91,12 +97,6 @@
       case CroupierState.Welcome:
         // data should be empty.
         assert(data == null);
-
-        // Start scanning for games if that's what's next for you.
-        if (nextState == CroupierState.JoinGame) {
-          settings_manager.scanSettings(); // don't wait for this future.
-        }
-
         break;
       case CroupierState.Settings:
         // data should be empty.
@@ -114,18 +114,20 @@
         GameType gt = data as GameType;
         game = cg.createGame(gt, 0); // Start as player 0 of whatever game type.
 
-        settings_manager
+        _advertiseFuture = settings_manager
             .createGameSyncgroup(gameTypeToString(gt), game.gameID)
             .then((GameStartData gsd) {
           // Only the game chooser should be advertising the game.
-          settings_manager
-              .advertiseSettings(gsd); // don't wait for this future.
-        });
+          return settings_manager.advertiseSettings(gsd);
+        }); // don't wait for this future.
 
         break;
       case CroupierState.JoinGame:
         // Note that if we were in join game, we must have been scanning.
-        settings_manager.stopScanSettings();
+        _scanFuture.then((_) {
+          settings_manager.stopScanSettings();
+          _scanFuture = null;
+        });
 
         if (data == null) {
           // Back button pressed.
@@ -148,7 +150,12 @@
         break;
       case CroupierState.ArrangePlayers:
         // Note that if we were arranging players, we might have been advertising.
-        settings_manager.stopAdvertiseSettings();
+        if (_advertiseFuture != null) {
+          _advertiseFuture.then((_) {
+            settings_manager.stopAdvertiseSettings();
+            _advertiseFuture = null;
+          });
+        }
 
         // data should be empty.
         // All rearrangements affect the Game's player number without changing app state.
@@ -173,6 +180,10 @@
     if (nextState == CroupierState.Welcome) {
       games_found = new Map<String, GameStartData>();
       players_found = new Map<int, int>();
+    } else if (nextState == CroupierState.JoinGame) {
+      // Start scanning for games since that's what's next for you.
+      _scanFuture =
+          settings_manager.scanSettings(); // don't wait for this future.
     }
 
     state = nextState;
diff --git a/lib/src/mocks/log_writer.dart b/lib/src/mocks/log_writer.dart
index 26e9075..19e6d58 100644
--- a/lib/src/mocks/log_writer.dart
+++ b/lib/src/mocks/log_writer.dart
@@ -6,10 +6,10 @@
 
 enum SimulLevel { TURN_BASED, INDEPENDENT, DEPENDENT }
 
-typedef void updateCallbackT(String key, String value);
+typedef void keyValueCallback(String key, String value);
 
 class LogWriter {
-  final updateCallbackT updateCallback;
+  final keyValueCallback updateCallback;
   final List<int> users;
   String logPrefix; // This can be completely ignored.
 
diff --git a/lib/src/mocks/settings_manager.dart b/lib/src/mocks/settings_manager.dart
index f6aac0a..71d497a 100644
--- a/lib/src/mocks/settings_manager.dart
+++ b/lib/src/mocks/settings_manager.dart
@@ -9,9 +9,9 @@
 import '../../logic/croupier_settings.dart' show CroupierSettings;
 
 class SettingsManager {
-  final util.updateCallbackT updateCallback;
-  final util.updateCallbackT updateGamesCallback;
-  final util.updateCallbackT updatePlayerFoundCallback;
+  final util.keyValueCallback updateCallback;
+  final util.keyValueCallback updateGamesCallback;
+  final util.keyValueCallback updatePlayerFoundCallback;
 
   SettingsManager(this.updateCallback, this.updateGamesCallback,
       this.updatePlayerFoundCallback);
@@ -44,13 +44,17 @@
     return new Future(() => null);
   }
 
-  void stopScanSettings() {}
+  Future stopScanSettings() {
+    return new Future(() => null);
+  }
 
   Future advertiseSettings(logic_game.GameStartData gsd) {
     return new Future(() => null);
   }
 
-  void stopAdvertiseSettings() {}
+  Future stopAdvertiseSettings() {
+    return new Future(() => null);
+  }
 
   Future createGameSyncgroup(String type, int gameID) {
     return new Future(() => null);
diff --git a/lib/src/mocks/util.dart b/lib/src/mocks/util.dart
new file mode 100644
index 0000000..e466b8d
--- /dev/null
+++ b/lib/src/mocks/util.dart
@@ -0,0 +1,5 @@
+// Copyright 2015 The Vanadium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+typedef void keyValueCallback(String key, String value);
diff --git a/lib/src/syncbase/discovery_client.dart b/lib/src/syncbase/discovery_client.dart
index bcf0482..51dcb9f 100644
--- a/lib/src/syncbase/discovery_client.dart
+++ b/lib/src/syncbase/discovery_client.dart
@@ -17,10 +17,13 @@
 /// Make this into the Dart Discovery client
 /// https://github.com/vanadium/issues/issues/835
 class DiscoveryClient {
-  final Map<String, ProxyHandlePair<discovery.AdvertiserProxy>> advertisers =
-      new Map<String, ProxyHandlePair<discovery.AdvertiserProxy>>();
-  final Map<String, ProxyHandlePair<discovery.ScannerProxy>> scanners =
-      new Map<String, ProxyHandlePair<discovery.ScannerProxy>>();
+  final Map<String,
+          Future<ProxyHandlePair<discovery.AdvertiserProxy>>> _advertisers =
+      new Map<String, Future<ProxyHandlePair<discovery.AdvertiserProxy>>>();
+  final Map<String, Future<ProxyHandlePair<discovery.ScannerProxy>>> _scanners =
+      new Map<String, Future<ProxyHandlePair<discovery.ScannerProxy>>>();
+  final Map<String, Future> _stoppingAdvertisers = new Map<String, Future>();
+  final Map<String, Future> _stoppingScanners = new Map<String, Future>();
 
   static final String discoveryUrl = 'https://mojo2.v.io/discovery.mojo';
 
@@ -46,77 +49,132 @@
   // Scans for this query and handles found/lost objects with the handler.
   // Keeps track of this scanner via the key.
   Future scan(String key, String query, discovery.ScanHandler handler) async {
-    // Cancel the scan if one is already going for this key.
-    if (scanners.containsKey(key)) {
-      stopScan(key);
+    // Return the existing scan if one is already going.
+    if (_scanners.containsKey(key)) {
+      return _scanners[key];
     }
 
-    discovery.ScannerProxy s = new discovery.ScannerProxy.unbound();
+    Future _scanHelper() async {
+      discovery.ScannerProxy s = new discovery.ScannerProxy.unbound();
 
-    print('Starting up discovery scanner ${key}. Looking for ${query}');
+      print('Starting up discovery scanner ${key}. Looking for ${query}');
 
-    shell.connectToService(discoveryUrl, s);
+      shell.connectToService(discoveryUrl, s);
 
-    // Use a ScanHandlerStub (Mojo-encodable interface) to wrap the scan handler.
-    discovery.ScanHandlerStub shs = new discovery.ScanHandlerStub.unbound();
-    shs.impl = handler;
+      // Use a ScanHandlerStub (Mojo-encodable interface) to wrap the scan handler.
+      discovery.ScanHandlerStub shs = new discovery.ScanHandlerStub.unbound();
+      shs.impl = handler;
 
-    print('Scanning begins!');
-    return s.ptr
-        .scan(query, shs)
-        .then((discovery.ScannerScanResponseParams response) {
-      print(
-          "${key} scanning started. The cancel handle is ${response.handle}.");
-      scanners[key] =
-          new ProxyHandlePair<discovery.ScannerProxy>(s, response.handle);
+      print('Scanning begins!');
+      return s.ptr
+          .scan(query, shs)
+          .then((discovery.ScannerScanResponseParams response) {
+        print(
+            "${key} scanning started. The cancel handle is ${response.handle}.");
+
+        return new ProxyHandlePair<discovery.ScannerProxy>(s, response.handle);
+      });
+    }
+
+    // Otherwise, set _scanners[key] and do the preparation inside the future
+    // so that stopScan can stop it if the two are called back to back.
+    _scanners[key] = _scanHelper();
+
+    return _scanners[key];
+  }
+
+  // This sends a stop signal to the scanner. Handles repeated stop calls on
+  // the same key by returning the same Future.
+  Future stopScan(String key) {
+    if (!_scanners.containsKey(key)) {
+      return new Future.value();
+    }
+    if (_stoppingScanners.containsKey(key)) {
+      return _stoppingScanners[key];
+    }
+
+    _stoppingScanners[key] = _stopScanHelper(key);
+
+    return _stoppingScanners[key].then((_) {
+      // Success! Let's clean up both _scanners and _stoppingScanners.
+      _scanners.remove(key);
+      _stoppingScanners.remove(key);
+    }).catchError((e) {
+      // Failure. We can only clean up _stoppingScanners.
+      _stoppingScanners.remove(key);
+      throw e;
     });
   }
 
-  // This sends a stop signal to the scanner. Since it is non-blocking, the
-  // scan handle may not stop instantaneously.
-  void stopScan(String key) {
-    if (scanners[key] != null) {
-      print("Stopping scan for ${key}.");
-      scanners[key].proxy.ptr.stop(scanners[key].handle);
-      scanners[key].proxy.close(); // don't wait for this future.
-      scanners.remove(key);
-    }
+  Future _stopScanHelper(String key) async {
+    ProxyHandlePair<discovery.ScannerProxy> sp = await _scanners[key];
+    await sp.proxy.ptr.stop(sp.handle);
+    await sp.proxy.close();
+    print("Scan was stopped for ${key}!");
   }
 
   // Advertises the given service information. Keeps track of the advertiser
   // handle via the key.
   Future advertise(String key, discovery.Service serviceInfo,
       {List<String> visibility}) async {
-    // Cancel the advertisement if one is already going for this key.
-    if (advertisers.containsKey(key)) {
-      stopAdvertise(key);
+    // Return the existing advertisement if one is already going.
+    if (_advertisers.containsKey(key)) {
+      return _advertisers[key];
     }
 
-    discovery.AdvertiserProxy a = new discovery.AdvertiserProxy.unbound();
+    Future _advertiseHelper() async {
+      discovery.AdvertiserProxy a = new discovery.AdvertiserProxy.unbound();
 
-    print(
-        'Starting up discovery advertiser ${key}. Broadcasting for ${serviceInfo.instanceName}');
-
-    shell.connectToService(discoveryUrl, a);
-
-    return a.ptr
-        .advertise(serviceInfo, visibility ?? <String>[])
-        .then((discovery.AdvertiserAdvertiseResponseParams response) {
       print(
-          "${key} advertising started. The cancel handle is ${response.handle}.");
-      advertisers[key] =
-          new ProxyHandlePair<discovery.AdvertiserProxy>(a, response.handle);
+          'Starting up discovery advertiser ${key}. Broadcasting for ${serviceInfo.instanceName}');
+
+      shell.connectToService(discoveryUrl, a);
+
+      return a.ptr
+          .advertise(serviceInfo, visibility ?? <String>[])
+          .then((discovery.AdvertiserAdvertiseResponseParams response) {
+        print(
+            "${key} advertising started. The cancel handle is ${response.handle}.");
+
+        return new ProxyHandlePair<discovery.AdvertiserProxy>(
+            a, response.handle);
+      });
+    }
+
+    // Otherwise, set _advertisers[key] and do the preparation inside the future
+    // so that stopAdvertise can stop it if the two are called back to back.
+    _advertisers[key] = _advertiseHelper();
+
+    return _advertisers[key];
+  }
+
+  // This sends a stop signal to the advertiser. Handles repeated stop calls on
+  // the same key by returning the same Future.
+  Future stopAdvertise(String key) {
+    if (!_advertisers.containsKey(key)) {
+      return new Future.value();
+    }
+    if (_stoppingAdvertisers.containsKey(key)) {
+      return _stoppingAdvertisers[key];
+    }
+
+    _stoppingAdvertisers[key] = _stopAdvertiseHelper(key);
+
+    return _stoppingAdvertisers[key].then((_) {
+      // Success! Let's clean up both _advertisers and _stoppingAdvertisers.
+      _advertisers.remove(key);
+      _stoppingAdvertisers.remove(key);
+    }).catchError((e) {
+      // Failure. We can only clean up _stoppingAdvertisers.
+      _stoppingAdvertisers.remove(key);
+      throw e;
     });
   }
 
-  // This sends a stop signal to the advertiser. Since it is non-blocking, the
-  // advertise handle may not stop instantaneously.
-  void stopAdvertise(String key) {
-    if (advertisers[key] != null) {
-      print("Stopping advertise for ${key}.");
-      advertisers[key].proxy.ptr.stop(advertisers[key].handle);
-      advertisers[key].proxy.close(); // don't wait for this future.
-      advertisers.remove(key);
-    }
+  Future _stopAdvertiseHelper(String key) async {
+    ProxyHandlePair<discovery.AdvertiserProxy> ap = await _advertisers[key];
+    await ap.proxy.ptr.stop(ap.handle);
+    await ap.proxy.close();
+    print("Advertise was stopped for ${key}!");
   }
 }
diff --git a/lib/src/syncbase/log_writer.dart b/lib/src/syncbase/log_writer.dart
index a588731..a146839 100644
--- a/lib/src/syncbase/log_writer.dart
+++ b/lib/src/syncbase/log_writer.dart
@@ -30,7 +30,7 @@
 
 class LogWriter {
   // This callback is called on each watch update, passing the key and value.
-  final util.updateCallbackT updateCallback;
+  final util.keyValueCallback updateCallback;
 
   // The users that we should look for when coming to a proposal consensus.
   final List<int> users;
diff --git a/lib/src/syncbase/settings_manager.dart b/lib/src/syncbase/settings_manager.dart
index 66fccee..7c11939 100644
--- a/lib/src/syncbase/settings_manager.dart
+++ b/lib/src/syncbase/settings_manager.dart
@@ -27,9 +27,9 @@
 import 'package:syncbase/syncbase_client.dart' as sc;
 
 class SettingsManager {
-  final util.updateCallbackT updateSettingsCallback;
-  final util.updateCallbackT updateGamesCallback;
-  final util.updateCallbackT updatePlayerFoundCallback;
+  final util.keyValueCallback updateSettingsCallback;
+  final util.keyValueCallback updateGamesCallback;
+  final util.keyValueCallback updatePlayerFoundCallback;
   final CroupierClient _cc;
   sc.SyncbaseTable tb;
 
@@ -59,8 +59,8 @@
     tb = await _cc.createTable(db, util.tableNameSettings);
 
     // Start to watch the stream for the shared settings table.
-    Stream<sc.WatchChange> watchStream = db.watch(util.tableNameSettings,
-        _settingsWatchSyncPrefix, UTF8.encode("now"));
+    Stream<sc.WatchChange> watchStream = db.watch(
+        util.tableNameSettings, _settingsWatchSyncPrefix, UTF8.encode("now"));
     _startWatchSettings(watchStream); // Don't wait for this future.
     _loadSettings(tb); // Don't wait for this future.
   }
@@ -198,7 +198,7 @@
         new logic_game.GameStartData(type, 0, gameID, id);
 
     await _cc.createSyncgroup(
-        _cc.makeSyncgroupName(util.syncgameSuffix(gsd.toJSONString())),
+        _cc.makeSyncgroupName(util.syncgameSuffix("${gsd.gameID}")),
         util.tableNameGames,
         prefix: util.syncgamePrefix(gameID));
 
@@ -250,30 +250,31 @@
   Future scanSettings() async {
     SettingsScanHandler ssh =
         new SettingsScanHandler(_cc, this.updateGamesCallback);
-    _cc.discoveryClient
-        .scan(_discoverySettingsKey, 'v.InterfaceName="${util.discoveryInterfaceName}"', ssh);
+    return _cc.discoveryClient.scan(_discoverySettingsKey,
+        'v.InterfaceName="${util.discoveryInterfaceName}"', ssh);
   }
 
-  void stopScanSettings() {
-    _cc.discoveryClient.stopScan(_discoverySettingsKey);
+  Future stopScanSettings() {
+    return _cc.discoveryClient.stopScan(_discoverySettingsKey);
   }
 
   // Someone who wants to join a game should advertise their presence.
   Future advertiseSettings(logic_game.GameStartData gsd) async {
     String suffix = await _syncSuffix();
-    String gameSuffix = util.syncgameSuffix(gsd.toJSONString());
-    _cc.discoveryClient.advertise(
+    String gameSuffix = util.syncgameSuffix("${gsd.gameID}");
+    return _cc.discoveryClient.advertise(
         _discoverySettingsKey,
         DiscoveryClient.serviceMaker(
             interfaceName: util.discoveryInterfaceName,
-            addrs: <String>[
-              _cc.makeSyncgroupName(suffix),
-              _cc.makeSyncgroupName(gameSuffix)
-            ]));
+            attrs: <String, String>{
+              util.syncgameSettingsAttr: _cc.makeSyncgroupName(suffix),
+              util.syncgameGameStartDataAttr: gsd.toJSONString()
+            },
+            addrs: <String>[_cc.makeSyncgroupName(gameSuffix)]));
   }
 
-  void stopAdvertiseSettings() {
-    _cc.discoveryClient.stopAdvertise(_discoverySettingsKey);
+  Future stopAdvertiseSettings() {
+    return _cc.discoveryClient.stopAdvertise(_discoverySettingsKey);
   }
 
   Future<int> _getUserID() async {
@@ -306,7 +307,7 @@
   CroupierClient _cc;
   Map<String, String> settingsAddrs;
   Map<String, String> gameAddrs;
-  util.updateCallbackT updateGamesCallback;
+  util.keyValueCallback updateGamesCallback;
 
   SettingsScanHandler(this._cc, this.updateGamesCallback) {
     settingsAddrs = new Map<String, String>();
@@ -317,15 +318,15 @@
     util.log(
         "SettingsScanHandler Found ${s.instanceId} ${s.instanceName} ${s.addrs}");
 
-    if (s.addrs.length == 2) {
-      // Note: Assumes 2 addresses.
-      settingsAddrs[s.instanceId] = s.addrs[0];
-      gameAddrs[s.instanceId] = s.addrs[1];
+    if (s.addrs.length == 1 && s.attrs != null) {
+      // Note: Assumes 1 address and attributes for the game.
+      settingsAddrs[s.instanceId] = s.attrs[util.syncgameSettingsAttr];
+      gameAddrs[s.instanceId] = s.addrs[0];
 
-      String json = _getPartFromBack(s.addrs[1], "-", 0);
-      updateGamesCallback(s.addrs[1], json);
+      String gameSettingsJSON = s.attrs[util.syncgameGameStartDataAttr];
+      updateGamesCallback(gameAddrs[s.instanceId], gameSettingsJSON);
 
-      _cc.joinSyncgroup(s.addrs[0]);
+      _cc.joinSyncgroup(settingsAddrs[s.instanceId]);
     } else {
       // An unexpected service was found. Who is advertising it?
       // https://github.com/vanadium/issues/issues/846
diff --git a/lib/src/syncbase/util.dart b/lib/src/syncbase/util.dart
index 1853bbe..4bc8bb2 100644
--- a/lib/src/syncbase/util.dart
+++ b/lib/src/syncbase/util.dart
@@ -4,25 +4,25 @@
 
 import 'package:syncbase/syncbase_client.dart' show Perms, SyncbaseClient;
 
-const appName = 'app';
-const dbName = 'db';
-const tableNameGames = 'games';
-const tableNameSettings = 'table_settings';
+const String appName = 'app';
+const String dbName = 'db';
+const String tableNameGames = 'games';
+const String tableNameSettings = 'table_settings';
 
 // TODO(alexfandrianto): This may need to be the global mount table with a
 // proxy. Otherwise, it will be difficult for other users to run.
 // https://github.com/vanadium/issues/issues/782
-const mtAddr = '/192.168.86.254:8101';
-const sgPrefix = 'croupierAlex/%%sync';
-const sgSuffix = 'discovery';
-const sgSuffixGame = 'gaming';
+const String mtAddr = '/192.168.86.254:8101';
+const String sgPrefix = 'croupierAlex/%%sync';
+const String sgSuffix = 'discovery';
+const String sgSuffixGame = 'gaming';
 
-const discoveryInterfaceName = 'CroupierSettingsAndGame2';
+const String discoveryInterfaceName = 'CroupierSettingsAndGame2';
 
 typedef void NoArgCb();
-typedef void updateCallbackT(String key, String value);
+typedef void keyValueCallback(String key, String value);
 
-String openPermsJson =
+const String openPermsJson =
     '{"Admin":{"In":["..."]},"Write":{"In":["..."]},"Read":{"In":["..."]},"Resolve":{"In":["..."]},"Debug":{"In":["..."]}}';
 Perms openPerms = SyncbaseClient.perms(openPermsJson);
 
@@ -40,3 +40,5 @@
   return "${gameID}";
 }
 
+const String syncgameSettingsAttr = "settings_sgname";
+const String syncgameGameStartDataAttr = "game_start_data";