From b41ed928490c454a7641a9cdf630126e22a716e6 Mon Sep 17 00:00:00 2001
From: pubkey <8926560+pubkey@users.noreply.github.com>
Date: Thu, 2 Dec 2021 21:57:50 +0100
Subject: [PATCH] 4.6.0

---
 CHANGELOG.md                        |   2 +
 dist/es5node/broadcast-channel.js   |  14 +-
 dist/es5node/index.js               |   6 +
 dist/es5node/leader-election.js     | 172 ++++++++++++++----------
 dist/es5node/methods/node.js        |   5 +-
 dist/es5node/util.js                |   4 +-
 dist/esbrowser/broadcast-channel.js |  11 ++
 dist/esbrowser/index.js             |   2 +-
 dist/esbrowser/leader-election.js   | 174 +++++++++++++++----------
 dist/esbrowser/methods/node.js      |   5 +-
 dist/esbrowser/util.js              |   1 +
 dist/esnode/broadcast-channel.js    |  11 ++
 dist/esnode/index.js                |   2 +-
 dist/esnode/leader-election.js      | 174 +++++++++++++++----------
 dist/esnode/methods/node.js         |   5 +-
 dist/esnode/util.js                 |   1 +
 dist/lib/broadcast-channel.js       |  14 +-
 dist/lib/browser.js                 | 194 ++++++++++++++++++----------
 dist/lib/browser.min.js             |   2 +-
 dist/lib/index.js                   |   6 +
 dist/lib/leader-election.js         | 172 ++++++++++++++----------
 dist/lib/methods/node.js            |   5 +-
 dist/lib/util.js                    |   4 +-
 docs/e2e.js                         | 194 ++++++++++++++++++----------
 docs/iframe.js                      | 194 ++++++++++++++++++----------
 docs/index.js                       | 194 ++++++++++++++++++----------
 docs/leader-iframe.js               | 194 ++++++++++++++++++----------
 docs/worker.js                      | 194 ++++++++++++++++++----------
 28 files changed, 1257 insertions(+), 699 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index b1ea5faa..4bfe57d2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,8 @@
 
 ## X.X.X (comming soon)
 
+## 4.6.0 (2 December 2021)
+
 Other:
   - Added `broadcastChannel.id()` for debugging
 
diff --git a/dist/es5node/broadcast-channel.js b/dist/es5node/broadcast-channel.js
index 5e2822a4..7b0114f1 100644
--- a/dist/es5node/broadcast-channel.js
+++ b/dist/es5node/broadcast-channel.js
@@ -3,7 +3,7 @@
 Object.defineProperty(exports, "__esModule", {
   value: true
 });
-exports.BroadcastChannel = void 0;
+exports.OPEN_BROADCAST_CHANNELS = exports.BroadcastChannel = void 0;
 exports.clearNodeFolder = clearNodeFolder;
 exports.enforceOptions = enforceOptions;
 
@@ -13,7 +13,18 @@ var _methodChooser = require("./method-chooser.js");
 
 var _options = require("./options.js");
 
+/**
+ * Contains all open channels,
+ * used in tests to ensure everything is closed.
+ */
+var OPEN_BROADCAST_CHANNELS = new Set();
+exports.OPEN_BROADCAST_CHANNELS = OPEN_BROADCAST_CHANNELS;
+var lastId = 0;
+
 var BroadcastChannel = function BroadcastChannel(name, options) {
+  // identifier of the channel to debug stuff
+  this.id = lastId++;
+  OPEN_BROADCAST_CHANNELS.add(this);
   this.name = name;
 
   if (ENFORCED_OPTIONS) {
@@ -154,6 +165,7 @@ BroadcastChannel.prototype = {
       return;
     }
 
+    OPEN_BROADCAST_CHANNELS["delete"](this);
     this.closed = true;
     var awaitPrepare = this._prepP ? this._prepP : _util.PROMISE_RESOLVED_VOID;
     this._onML = null;
diff --git a/dist/es5node/index.js b/dist/es5node/index.js
index 8bc266af..f02b5343 100644
--- a/dist/es5node/index.js
+++ b/dist/es5node/index.js
@@ -9,6 +9,12 @@ Object.defineProperty(exports, "BroadcastChannel", {
     return _broadcastChannel.BroadcastChannel;
   }
 });
+Object.defineProperty(exports, "OPEN_BROADCAST_CHANNELS", {
+  enumerable: true,
+  get: function get() {
+    return _broadcastChannel.OPEN_BROADCAST_CHANNELS;
+  }
+});
 Object.defineProperty(exports, "beLeader", {
   enumerable: true,
   get: function get() {
diff --git a/dist/es5node/leader-election.js b/dist/es5node/leader-election.js
index 86fe742c..31424cb0 100644
--- a/dist/es5node/leader-election.js
+++ b/dist/es5node/leader-election.js
@@ -20,15 +20,14 @@ var LeaderElection = function LeaderElection(broadcastChannel, options) {
   this.isDead = false;
   this.token = (0, _util.randomToken)();
   /**
-   * _isApplying
-   * Only set when a leader application is
-   * running at the moment.
-   * @type {Promise<any> | null}
+   * Apply Queue,
+   * used to ensure we do not run applyOnce()
+   * in parallel.
    */
 
-  this._isApl = false; // _isApplying
+  this._aplQ = _util.PROMISE_RESOLVED_VOID; // amount of unfinished applyOnce() calls
 
-  this._reApply = false; // things to clean up
+  this._aplQC = 0; // things to clean up
 
   this._unl = []; // _unloads
 
@@ -65,6 +64,11 @@ var LeaderElection = function LeaderElection(broadcastChannel, options) {
 };
 
 LeaderElection.prototype = {
+  /**
+   * Returns true if the instance is leader,
+   * false if not.
+   * @async
+   */
   applyOnce: function applyOnce() {
     var _this2 = this;
 
@@ -73,82 +77,113 @@ LeaderElection.prototype = {
     }
 
     if (this.isDead) {
-      return _util.PROMISE_RESOLVED_FALSE;
-    } // do nothing if already running
+      return (0, _util.sleep)(0, false);
+    }
+    /**
+     * Already applying more then once,
+     * -> wait for the apply queue to be finished.
+     */
 
 
-    if (this._isApl) {
-      this._reApply = true;
-      return (0, _util.sleep)(0, false);
+    if (this._aplQC > 1) {
+      return this._aplQ;
     }
+    /**
+     * Add a new apply-run
+     */
 
-    var stopCriteria = false;
-    var recieved = [];
 
-    var handleMessage = function handleMessage(msg) {
-      if (msg.context === 'leader' && msg.token != _this2.token) {
-        recieved.push(msg);
+    var applyRun = function applyRun() {
+      /**
+       * Optimization shortcuts.
+       * Directly return if a previous run
+       * has already elected a leader.
+       */
+      if (_this2.isLeader) {
+        return _util.PROMISE_RESOLVED_TRUE;
+      }
 
-        if (msg.action === 'apply') {
-          // other is applying
-          if (msg.token > _this2.token) {
-            // other has higher token, stop applying
-            stopCriteria = true;
-          }
-        }
+      var stopCriteria = false;
+      var stopCriteriaPromiseResolve;
+      /**
+       * Resolves when a stop criteria is reached.
+       * Uses as a performance shortcut so we do not
+       * have to await the responseTime when it is already clear
+       * that the election failed.
+       */
 
-        if (msg.action === 'tell') {
-          // other is already leader
+      var stopCriteriaPromise = new Promise(function (res) {
+        stopCriteriaPromiseResolve = function stopCriteriaPromiseResolve() {
           stopCriteria = true;
-          _this2.hasLeader = true;
+          res();
+        };
+      });
+      var recieved = [];
+
+      var handleMessage = function handleMessage(msg) {
+        if (msg.context === 'leader' && msg.token != _this2.token) {
+          recieved.push(msg);
+
+          if (msg.action === 'apply') {
+            // other is applying
+            if (msg.token > _this2.token) {
+              /**
+               * other has higher token
+               * -> stop applying and let other become leader.
+               */
+              stopCriteriaPromiseResolve();
+            }
+          }
+
+          if (msg.action === 'tell') {
+            // other is already leader
+            stopCriteriaPromiseResolve();
+            _this2.hasLeader = true;
+          }
         }
-      }
-    };
+      };
 
-    this.broadcastChannel.addEventListener('internal', handleMessage);
+      _this2.broadcastChannel.addEventListener('internal', handleMessage);
 
-    var applyPromise = _sendMessage(this, 'apply') // send out that this one is applying
-    .then(function () {
-      return (0, _util.sleep)(_this2._options.responseTime);
-    }) // let others time to respond
-    .then(function () {
-      if (stopCriteria) {
-        return Promise.reject(new Error());
-      } else {
+      var applyPromise = _sendMessage(_this2, 'apply') // send out that this one is applying
+      .then(function () {
+        return Promise.race([(0, _util.sleep)(_this2._options.responseTime / 2), stopCriteriaPromise.then(function () {
+          return Promise.reject(new Error());
+        })]);
+      }) // send again in case another instance was just created
+      .then(function () {
         return _sendMessage(_this2, 'apply');
-      }
-    }).then(function () {
-      return (0, _util.sleep)(_this2._options.responseTime);
-    }) // let others time to respond
-    .then(function () {
-      if (stopCriteria) {
-        return Promise.reject(new Error());
-      } else {
-        return _sendMessage(_this2);
-      }
+      }) // let others time to respond
+      .then(function () {
+        return Promise.race([(0, _util.sleep)(_this2._options.responseTime / 2), stopCriteriaPromise.then(function () {
+          return Promise.reject(new Error());
+        })]);
+      })["catch"](function () {}).then(function () {
+        _this2.broadcastChannel.removeEventListener('internal', handleMessage);
+
+        if (!stopCriteria) {
+          // no stop criteria -> own is leader
+          return beLeader(_this2).then(function () {
+            return true;
+          });
+        } else {
+          // other is leader
+          return false;
+        }
+      });
+
+      return applyPromise;
+    };
+
+    this._aplQC = this._aplQC + 1;
+    this._aplQ = this._aplQ.then(function () {
+      return applyRun();
     }).then(function () {
-      return beLeader(_this2);
-    }) // no one disagreed -> this one is now leader
-    .then(function () {
-      return true;
-    })["catch"](function () {
-      return false;
-    }) // apply not successfull
-    .then(function (success) {
-      _this2.broadcastChannel.removeEventListener('internal', handleMessage);
-
-      _this2._isApl = false;
-
-      if (!success && _this2._reApply) {
-        _this2._reApply = false;
-        return _this2.applyOnce();
-      } else {
-        return success;
-      }
+      _this2._aplQC = _this2._aplQC - 1;
+    });
+    return this._aplQ.then(function () {
+      return _this2.isLeader;
     });
-
-    this._isApl = applyPromise;
-    return applyPromise;
   },
   awaitLeadership: function awaitLeadership() {
     if (
@@ -225,6 +260,7 @@ function _awaitLeadershipOnce(leaderElector) {
     }); // try on fallbackInterval
 
     var interval = setInterval(function () {
+      console.log('applyOnce via fallbackInterval');
       leaderElector.applyOnce().then(function () {
         if (leaderElector.isLeader) {
           finish();
diff --git a/dist/es5node/methods/node.js b/dist/es5node/methods/node.js
index 3a0f716b..4c142626 100644
--- a/dist/es5node/methods/node.js
+++ b/dist/es5node/methods/node.js
@@ -1066,7 +1066,10 @@ function postMessage(channelState, messageJson) {
 
 
 function emitOverFastPath(state, msgObj, messageJson) {
-  if (!state.options.node.useFastPath) return; // disabled
+  if (!state.options.node.useFastPath) {
+    // disabled
+    return;
+  }
 
   var others = OTHER_INSTANCES[state.channelName].filter(function (s) {
     return s !== state;
diff --git a/dist/es5node/util.js b/dist/es5node/util.js
index 1afac5ba..c70aec48 100644
--- a/dist/es5node/util.js
+++ b/dist/es5node/util.js
@@ -3,7 +3,7 @@
 Object.defineProperty(exports, "__esModule", {
   value: true
 });
-exports.isNode = exports.PROMISE_RESOLVED_VOID = exports.PROMISE_RESOLVED_FALSE = void 0;
+exports.isNode = exports.PROMISE_RESOLVED_VOID = exports.PROMISE_RESOLVED_TRUE = exports.PROMISE_RESOLVED_FALSE = void 0;
 exports.isPromise = isPromise;
 exports.microSeconds = microSeconds;
 exports.randomInt = randomInt;
@@ -23,6 +23,8 @@ function isPromise(obj) {
 
 var PROMISE_RESOLVED_FALSE = Promise.resolve(false);
 exports.PROMISE_RESOLVED_FALSE = PROMISE_RESOLVED_FALSE;
+var PROMISE_RESOLVED_TRUE = Promise.resolve(true);
+exports.PROMISE_RESOLVED_TRUE = PROMISE_RESOLVED_TRUE;
 var PROMISE_RESOLVED_VOID = Promise.resolve();
 exports.PROMISE_RESOLVED_VOID = PROMISE_RESOLVED_VOID;
 
diff --git a/dist/esbrowser/broadcast-channel.js b/dist/esbrowser/broadcast-channel.js
index bdccd05e..02e5f09b 100644
--- a/dist/esbrowser/broadcast-channel.js
+++ b/dist/esbrowser/broadcast-channel.js
@@ -1,7 +1,17 @@
 import { isPromise, PROMISE_RESOLVED_FALSE, PROMISE_RESOLVED_VOID } from './util.js';
 import { chooseMethod } from './method-chooser.js';
 import { fillOptionsWithDefaults } from './options.js';
+/**
+ * Contains all open channels,
+ * used in tests to ensure everything is closed.
+ */
+
+export var OPEN_BROADCAST_CHANNELS = new Set();
+var lastId = 0;
 export var BroadcastChannel = function BroadcastChannel(name, options) {
+  // identifier of the channel to debug stuff
+  this.id = lastId++;
+  OPEN_BROADCAST_CHANNELS.add(this);
   this.name = name;
 
   if (ENFORCED_OPTIONS) {
@@ -137,6 +147,7 @@ BroadcastChannel.prototype = {
       return;
     }
 
+    OPEN_BROADCAST_CHANNELS["delete"](this);
     this.closed = true;
     var awaitPrepare = this._prepP ? this._prepP : PROMISE_RESOLVED_VOID;
     this._onML = null;
diff --git a/dist/esbrowser/index.js b/dist/esbrowser/index.js
index 0338ab48..cc1337b1 100644
--- a/dist/esbrowser/index.js
+++ b/dist/esbrowser/index.js
@@ -1,2 +1,2 @@
-export { BroadcastChannel, clearNodeFolder, enforceOptions } from './broadcast-channel';
+export { BroadcastChannel, clearNodeFolder, enforceOptions, OPEN_BROADCAST_CHANNELS } from './broadcast-channel';
 export { createLeaderElection, beLeader } from './leader-election';
\ No newline at end of file
diff --git a/dist/esbrowser/leader-election.js b/dist/esbrowser/leader-election.js
index 642409b4..ee16e48d 100644
--- a/dist/esbrowser/leader-election.js
+++ b/dist/esbrowser/leader-election.js
@@ -1,4 +1,4 @@
-import { sleep, randomToken, PROMISE_RESOLVED_FALSE, PROMISE_RESOLVED_VOID } from './util.js';
+import { sleep, randomToken, PROMISE_RESOLVED_VOID, PROMISE_RESOLVED_TRUE } from './util.js';
 import { add as unloadAdd } from 'unload';
 
 var LeaderElection = function LeaderElection(broadcastChannel, options) {
@@ -11,15 +11,14 @@ var LeaderElection = function LeaderElection(broadcastChannel, options) {
   this.isDead = false;
   this.token = randomToken();
   /**
-   * _isApplying
-   * Only set when a leader application is
-   * running at the moment.
-   * @type {Promise<any> | null}
+   * Apply Queue,
+   * used to ensure we do not run applyOnce()
+   * in parallel.
    */
 
-  this._isApl = false; // _isApplying
+  this._aplQ = PROMISE_RESOLVED_VOID; // amount of unfinished applyOnce() calls
 
-  this._reApply = false; // things to clean up
+  this._aplQC = 0; // things to clean up
 
   this._unl = []; // _unloads
 
@@ -56,6 +55,11 @@ var LeaderElection = function LeaderElection(broadcastChannel, options) {
 };
 
 LeaderElection.prototype = {
+  /**
+   * Returns true if the instance is leader,
+   * false if not.
+   * @async
+   */
   applyOnce: function applyOnce() {
     var _this2 = this;
 
@@ -64,82 +68,113 @@ LeaderElection.prototype = {
     }
 
     if (this.isDead) {
-      return PROMISE_RESOLVED_FALSE;
-    } // do nothing if already running
+      return sleep(0, false);
+    }
+    /**
+     * Already applying more then once,
+     * -> wait for the apply queue to be finished.
+     */
 
 
-    if (this._isApl) {
-      this._reApply = true;
-      return sleep(0, false);
+    if (this._aplQC > 1) {
+      return this._aplQ;
     }
+    /**
+     * Add a new apply-run
+     */
 
-    var stopCriteria = false;
-    var recieved = [];
 
-    var handleMessage = function handleMessage(msg) {
-      if (msg.context === 'leader' && msg.token != _this2.token) {
-        recieved.push(msg);
+    var applyRun = function applyRun() {
+      /**
+       * Optimization shortcuts.
+       * Directly return if a previous run
+       * has already elected a leader.
+       */
+      if (_this2.isLeader) {
+        return PROMISE_RESOLVED_TRUE;
+      }
 
-        if (msg.action === 'apply') {
-          // other is applying
-          if (msg.token > _this2.token) {
-            // other has higher token, stop applying
-            stopCriteria = true;
-          }
-        }
+      var stopCriteria = false;
+      var stopCriteriaPromiseResolve;
+      /**
+       * Resolves when a stop criteria is reached.
+       * Uses as a performance shortcut so we do not
+       * have to await the responseTime when it is already clear
+       * that the election failed.
+       */
 
-        if (msg.action === 'tell') {
-          // other is already leader
+      var stopCriteriaPromise = new Promise(function (res) {
+        stopCriteriaPromiseResolve = function stopCriteriaPromiseResolve() {
           stopCriteria = true;
-          _this2.hasLeader = true;
+          res();
+        };
+      });
+      var recieved = [];
+
+      var handleMessage = function handleMessage(msg) {
+        if (msg.context === 'leader' && msg.token != _this2.token) {
+          recieved.push(msg);
+
+          if (msg.action === 'apply') {
+            // other is applying
+            if (msg.token > _this2.token) {
+              /**
+               * other has higher token
+               * -> stop applying and let other become leader.
+               */
+              stopCriteriaPromiseResolve();
+            }
+          }
+
+          if (msg.action === 'tell') {
+            // other is already leader
+            stopCriteriaPromiseResolve();
+            _this2.hasLeader = true;
+          }
         }
-      }
-    };
+      };
 
-    this.broadcastChannel.addEventListener('internal', handleMessage);
+      _this2.broadcastChannel.addEventListener('internal', handleMessage);
 
-    var applyPromise = _sendMessage(this, 'apply') // send out that this one is applying
-    .then(function () {
-      return sleep(_this2._options.responseTime);
-    }) // let others time to respond
-    .then(function () {
-      if (stopCriteria) {
-        return Promise.reject(new Error());
-      } else {
+      var applyPromise = _sendMessage(_this2, 'apply') // send out that this one is applying
+      .then(function () {
+        return Promise.race([sleep(_this2._options.responseTime / 2), stopCriteriaPromise.then(function () {
+          return Promise.reject(new Error());
+        })]);
+      }) // send again in case another instance was just created
+      .then(function () {
         return _sendMessage(_this2, 'apply');
-      }
-    }).then(function () {
-      return sleep(_this2._options.responseTime);
-    }) // let others time to respond
-    .then(function () {
-      if (stopCriteria) {
-        return Promise.reject(new Error());
-      } else {
-        return _sendMessage(_this2);
-      }
+      }) // let others time to respond
+      .then(function () {
+        return Promise.race([sleep(_this2._options.responseTime / 2), stopCriteriaPromise.then(function () {
+          return Promise.reject(new Error());
+        })]);
+      })["catch"](function () {}).then(function () {
+        _this2.broadcastChannel.removeEventListener('internal', handleMessage);
+
+        if (!stopCriteria) {
+          // no stop criteria -> own is leader
+          return beLeader(_this2).then(function () {
+            return true;
+          });
+        } else {
+          // other is leader
+          return false;
+        }
+      });
+
+      return applyPromise;
+    };
+
+    this._aplQC = this._aplQC + 1;
+    this._aplQ = this._aplQ.then(function () {
+      return applyRun();
     }).then(function () {
-      return beLeader(_this2);
-    }) // no one disagreed -> this one is now leader
-    .then(function () {
-      return true;
-    })["catch"](function () {
-      return false;
-    }) // apply not successfull
-    .then(function (success) {
-      _this2.broadcastChannel.removeEventListener('internal', handleMessage);
-
-      _this2._isApl = false;
-
-      if (!success && _this2._reApply) {
-        _this2._reApply = false;
-        return _this2.applyOnce();
-      } else {
-        return success;
-      }
+      _this2._aplQC = _this2._aplQC - 1;
+    });
+    return this._aplQ.then(function () {
+      return _this2.isLeader;
     });
-
-    this._isApl = applyPromise;
-    return applyPromise;
   },
   awaitLeadership: function awaitLeadership() {
     if (
@@ -216,6 +251,7 @@ function _awaitLeadershipOnce(leaderElector) {
     }); // try on fallbackInterval
 
     var interval = setInterval(function () {
+      console.log('applyOnce via fallbackInterval');
       leaderElector.applyOnce().then(function () {
         if (leaderElector.isLeader) {
           finish();
diff --git a/dist/esbrowser/methods/node.js b/dist/esbrowser/methods/node.js
index 5bb0e50f..880bf616 100644
--- a/dist/esbrowser/methods/node.js
+++ b/dist/esbrowser/methods/node.js
@@ -975,7 +975,10 @@ export function postMessage(channelState, messageJson) {
  */
 
 export function emitOverFastPath(state, msgObj, messageJson) {
-  if (!state.options.node.useFastPath) return; // disabled
+  if (!state.options.node.useFastPath) {
+    // disabled
+    return;
+  }
 
   var others = OTHER_INSTANCES[state.channelName].filter(function (s) {
     return s !== state;
diff --git a/dist/esbrowser/util.js b/dist/esbrowser/util.js
index c6febc5a..5d81fdcd 100644
--- a/dist/esbrowser/util.js
+++ b/dist/esbrowser/util.js
@@ -9,6 +9,7 @@ export function isPromise(obj) {
   }
 }
 export var PROMISE_RESOLVED_FALSE = Promise.resolve(false);
+export var PROMISE_RESOLVED_TRUE = Promise.resolve(true);
 export var PROMISE_RESOLVED_VOID = Promise.resolve();
 export function sleep(time, resolveWith) {
   if (!time) time = 0;
diff --git a/dist/esnode/broadcast-channel.js b/dist/esnode/broadcast-channel.js
index bdccd05e..02e5f09b 100644
--- a/dist/esnode/broadcast-channel.js
+++ b/dist/esnode/broadcast-channel.js
@@ -1,7 +1,17 @@
 import { isPromise, PROMISE_RESOLVED_FALSE, PROMISE_RESOLVED_VOID } from './util.js';
 import { chooseMethod } from './method-chooser.js';
 import { fillOptionsWithDefaults } from './options.js';
+/**
+ * Contains all open channels,
+ * used in tests to ensure everything is closed.
+ */
+
+export var OPEN_BROADCAST_CHANNELS = new Set();
+var lastId = 0;
 export var BroadcastChannel = function BroadcastChannel(name, options) {
+  // identifier of the channel to debug stuff
+  this.id = lastId++;
+  OPEN_BROADCAST_CHANNELS.add(this);
   this.name = name;
 
   if (ENFORCED_OPTIONS) {
@@ -137,6 +147,7 @@ BroadcastChannel.prototype = {
       return;
     }
 
+    OPEN_BROADCAST_CHANNELS["delete"](this);
     this.closed = true;
     var awaitPrepare = this._prepP ? this._prepP : PROMISE_RESOLVED_VOID;
     this._onML = null;
diff --git a/dist/esnode/index.js b/dist/esnode/index.js
index 0338ab48..cc1337b1 100644
--- a/dist/esnode/index.js
+++ b/dist/esnode/index.js
@@ -1,2 +1,2 @@
-export { BroadcastChannel, clearNodeFolder, enforceOptions } from './broadcast-channel';
+export { BroadcastChannel, clearNodeFolder, enforceOptions, OPEN_BROADCAST_CHANNELS } from './broadcast-channel';
 export { createLeaderElection, beLeader } from './leader-election';
\ No newline at end of file
diff --git a/dist/esnode/leader-election.js b/dist/esnode/leader-election.js
index 642409b4..ee16e48d 100644
--- a/dist/esnode/leader-election.js
+++ b/dist/esnode/leader-election.js
@@ -1,4 +1,4 @@
-import { sleep, randomToken, PROMISE_RESOLVED_FALSE, PROMISE_RESOLVED_VOID } from './util.js';
+import { sleep, randomToken, PROMISE_RESOLVED_VOID, PROMISE_RESOLVED_TRUE } from './util.js';
 import { add as unloadAdd } from 'unload';
 
 var LeaderElection = function LeaderElection(broadcastChannel, options) {
@@ -11,15 +11,14 @@ var LeaderElection = function LeaderElection(broadcastChannel, options) {
   this.isDead = false;
   this.token = randomToken();
   /**
-   * _isApplying
-   * Only set when a leader application is
-   * running at the moment.
-   * @type {Promise<any> | null}
+   * Apply Queue,
+   * used to ensure we do not run applyOnce()
+   * in parallel.
    */
 
-  this._isApl = false; // _isApplying
+  this._aplQ = PROMISE_RESOLVED_VOID; // amount of unfinished applyOnce() calls
 
-  this._reApply = false; // things to clean up
+  this._aplQC = 0; // things to clean up
 
   this._unl = []; // _unloads
 
@@ -56,6 +55,11 @@ var LeaderElection = function LeaderElection(broadcastChannel, options) {
 };
 
 LeaderElection.prototype = {
+  /**
+   * Returns true if the instance is leader,
+   * false if not.
+   * @async
+   */
   applyOnce: function applyOnce() {
     var _this2 = this;
 
@@ -64,82 +68,113 @@ LeaderElection.prototype = {
     }
 
     if (this.isDead) {
-      return PROMISE_RESOLVED_FALSE;
-    } // do nothing if already running
+      return sleep(0, false);
+    }
+    /**
+     * Already applying more then once,
+     * -> wait for the apply queue to be finished.
+     */
 
 
-    if (this._isApl) {
-      this._reApply = true;
-      return sleep(0, false);
+    if (this._aplQC > 1) {
+      return this._aplQ;
     }
+    /**
+     * Add a new apply-run
+     */
 
-    var stopCriteria = false;
-    var recieved = [];
 
-    var handleMessage = function handleMessage(msg) {
-      if (msg.context === 'leader' && msg.token != _this2.token) {
-        recieved.push(msg);
+    var applyRun = function applyRun() {
+      /**
+       * Optimization shortcuts.
+       * Directly return if a previous run
+       * has already elected a leader.
+       */
+      if (_this2.isLeader) {
+        return PROMISE_RESOLVED_TRUE;
+      }
 
-        if (msg.action === 'apply') {
-          // other is applying
-          if (msg.token > _this2.token) {
-            // other has higher token, stop applying
-            stopCriteria = true;
-          }
-        }
+      var stopCriteria = false;
+      var stopCriteriaPromiseResolve;
+      /**
+       * Resolves when a stop criteria is reached.
+       * Uses as a performance shortcut so we do not
+       * have to await the responseTime when it is already clear
+       * that the election failed.
+       */
 
-        if (msg.action === 'tell') {
-          // other is already leader
+      var stopCriteriaPromise = new Promise(function (res) {
+        stopCriteriaPromiseResolve = function stopCriteriaPromiseResolve() {
           stopCriteria = true;
-          _this2.hasLeader = true;
+          res();
+        };
+      });
+      var recieved = [];
+
+      var handleMessage = function handleMessage(msg) {
+        if (msg.context === 'leader' && msg.token != _this2.token) {
+          recieved.push(msg);
+
+          if (msg.action === 'apply') {
+            // other is applying
+            if (msg.token > _this2.token) {
+              /**
+               * other has higher token
+               * -> stop applying and let other become leader.
+               */
+              stopCriteriaPromiseResolve();
+            }
+          }
+
+          if (msg.action === 'tell') {
+            // other is already leader
+            stopCriteriaPromiseResolve();
+            _this2.hasLeader = true;
+          }
         }
-      }
-    };
+      };
 
-    this.broadcastChannel.addEventListener('internal', handleMessage);
+      _this2.broadcastChannel.addEventListener('internal', handleMessage);
 
-    var applyPromise = _sendMessage(this, 'apply') // send out that this one is applying
-    .then(function () {
-      return sleep(_this2._options.responseTime);
-    }) // let others time to respond
-    .then(function () {
-      if (stopCriteria) {
-        return Promise.reject(new Error());
-      } else {
+      var applyPromise = _sendMessage(_this2, 'apply') // send out that this one is applying
+      .then(function () {
+        return Promise.race([sleep(_this2._options.responseTime / 2), stopCriteriaPromise.then(function () {
+          return Promise.reject(new Error());
+        })]);
+      }) // send again in case another instance was just created
+      .then(function () {
         return _sendMessage(_this2, 'apply');
-      }
-    }).then(function () {
-      return sleep(_this2._options.responseTime);
-    }) // let others time to respond
-    .then(function () {
-      if (stopCriteria) {
-        return Promise.reject(new Error());
-      } else {
-        return _sendMessage(_this2);
-      }
+      }) // let others time to respond
+      .then(function () {
+        return Promise.race([sleep(_this2._options.responseTime / 2), stopCriteriaPromise.then(function () {
+          return Promise.reject(new Error());
+        })]);
+      })["catch"](function () {}).then(function () {
+        _this2.broadcastChannel.removeEventListener('internal', handleMessage);
+
+        if (!stopCriteria) {
+          // no stop criteria -> own is leader
+          return beLeader(_this2).then(function () {
+            return true;
+          });
+        } else {
+          // other is leader
+          return false;
+        }
+      });
+
+      return applyPromise;
+    };
+
+    this._aplQC = this._aplQC + 1;
+    this._aplQ = this._aplQ.then(function () {
+      return applyRun();
     }).then(function () {
-      return beLeader(_this2);
-    }) // no one disagreed -> this one is now leader
-    .then(function () {
-      return true;
-    })["catch"](function () {
-      return false;
-    }) // apply not successfull
-    .then(function (success) {
-      _this2.broadcastChannel.removeEventListener('internal', handleMessage);
-
-      _this2._isApl = false;
-
-      if (!success && _this2._reApply) {
-        _this2._reApply = false;
-        return _this2.applyOnce();
-      } else {
-        return success;
-      }
+      _this2._aplQC = _this2._aplQC - 1;
+    });
+    return this._aplQ.then(function () {
+      return _this2.isLeader;
     });
-
-    this._isApl = applyPromise;
-    return applyPromise;
   },
   awaitLeadership: function awaitLeadership() {
     if (
@@ -216,6 +251,7 @@ function _awaitLeadershipOnce(leaderElector) {
     }); // try on fallbackInterval
 
     var interval = setInterval(function () {
+      console.log('applyOnce via fallbackInterval');
       leaderElector.applyOnce().then(function () {
         if (leaderElector.isLeader) {
           finish();
diff --git a/dist/esnode/methods/node.js b/dist/esnode/methods/node.js
index 5bb0e50f..880bf616 100644
--- a/dist/esnode/methods/node.js
+++ b/dist/esnode/methods/node.js
@@ -975,7 +975,10 @@ export function postMessage(channelState, messageJson) {
  */
 
 export function emitOverFastPath(state, msgObj, messageJson) {
-  if (!state.options.node.useFastPath) return; // disabled
+  if (!state.options.node.useFastPath) {
+    // disabled
+    return;
+  }
 
   var others = OTHER_INSTANCES[state.channelName].filter(function (s) {
     return s !== state;
diff --git a/dist/esnode/util.js b/dist/esnode/util.js
index c6febc5a..5d81fdcd 100644
--- a/dist/esnode/util.js
+++ b/dist/esnode/util.js
@@ -9,6 +9,7 @@ export function isPromise(obj) {
   }
 }
 export var PROMISE_RESOLVED_FALSE = Promise.resolve(false);
+export var PROMISE_RESOLVED_TRUE = Promise.resolve(true);
 export var PROMISE_RESOLVED_VOID = Promise.resolve();
 export function sleep(time, resolveWith) {
   if (!time) time = 0;
diff --git a/dist/lib/broadcast-channel.js b/dist/lib/broadcast-channel.js
index 5e2822a4..7b0114f1 100644
--- a/dist/lib/broadcast-channel.js
+++ b/dist/lib/broadcast-channel.js
@@ -3,7 +3,7 @@
 Object.defineProperty(exports, "__esModule", {
   value: true
 });
-exports.BroadcastChannel = void 0;
+exports.OPEN_BROADCAST_CHANNELS = exports.BroadcastChannel = void 0;
 exports.clearNodeFolder = clearNodeFolder;
 exports.enforceOptions = enforceOptions;
 
@@ -13,7 +13,18 @@ var _methodChooser = require("./method-chooser.js");
 
 var _options = require("./options.js");
 
+/**
+ * Contains all open channels,
+ * used in tests to ensure everything is closed.
+ */
+var OPEN_BROADCAST_CHANNELS = new Set();
+exports.OPEN_BROADCAST_CHANNELS = OPEN_BROADCAST_CHANNELS;
+var lastId = 0;
+
 var BroadcastChannel = function BroadcastChannel(name, options) {
+  // identifier of the channel to debug stuff
+  this.id = lastId++;
+  OPEN_BROADCAST_CHANNELS.add(this);
   this.name = name;
 
   if (ENFORCED_OPTIONS) {
@@ -154,6 +165,7 @@ BroadcastChannel.prototype = {
       return;
     }
 
+    OPEN_BROADCAST_CHANNELS["delete"](this);
     this.closed = true;
     var awaitPrepare = this._prepP ? this._prepP : _util.PROMISE_RESOLVED_VOID;
     this._onML = null;
diff --git a/dist/lib/browser.js b/dist/lib/browser.js
index 0e415fb6..66d38400 100644
--- a/dist/lib/browser.js
+++ b/dist/lib/browser.js
@@ -4,7 +4,7 @@
 Object.defineProperty(exports, "__esModule", {
   value: true
 });
-exports.BroadcastChannel = void 0;
+exports.OPEN_BROADCAST_CHANNELS = exports.BroadcastChannel = void 0;
 exports.clearNodeFolder = clearNodeFolder;
 exports.enforceOptions = enforceOptions;
 
@@ -14,7 +14,18 @@ var _methodChooser = require("./method-chooser.js");
 
 var _options = require("./options.js");
 
+/**
+ * Contains all open channels,
+ * used in tests to ensure everything is closed.
+ */
+var OPEN_BROADCAST_CHANNELS = new Set();
+exports.OPEN_BROADCAST_CHANNELS = OPEN_BROADCAST_CHANNELS;
+var lastId = 0;
+
 var BroadcastChannel = function BroadcastChannel(name, options) {
+  // identifier of the channel to debug stuff
+  this.id = lastId++;
+  OPEN_BROADCAST_CHANNELS.add(this);
   this.name = name;
 
   if (ENFORCED_OPTIONS) {
@@ -155,6 +166,7 @@ BroadcastChannel.prototype = {
       return;
     }
 
+    OPEN_BROADCAST_CHANNELS["delete"](this);
     this.closed = true;
     var awaitPrepare = this._prepP ? this._prepP : _util.PROMISE_RESOLVED_VOID;
     this._onML = null;
@@ -319,6 +331,12 @@ Object.defineProperty(exports, "BroadcastChannel", {
     return _broadcastChannel.BroadcastChannel;
   }
 });
+Object.defineProperty(exports, "OPEN_BROADCAST_CHANNELS", {
+  enumerable: true,
+  get: function get() {
+    return _broadcastChannel.OPEN_BROADCAST_CHANNELS;
+  }
+});
 Object.defineProperty(exports, "beLeader", {
   enumerable: true,
   get: function get() {
@@ -370,15 +388,14 @@ var LeaderElection = function LeaderElection(broadcastChannel, options) {
   this.isDead = false;
   this.token = (0, _util.randomToken)();
   /**
-   * _isApplying
-   * Only set when a leader application is
-   * running at the moment.
-   * @type {Promise<any> | null}
+   * Apply Queue,
+   * used to ensure we do not run applyOnce()
+   * in parallel.
    */
 
-  this._isApl = false; // _isApplying
+  this._aplQ = _util.PROMISE_RESOLVED_VOID; // amount of unfinished applyOnce() calls
 
-  this._reApply = false; // things to clean up
+  this._aplQC = 0; // things to clean up
 
   this._unl = []; // _unloads
 
@@ -415,6 +432,11 @@ var LeaderElection = function LeaderElection(broadcastChannel, options) {
 };
 
 LeaderElection.prototype = {
+  /**
+   * Returns true if the instance is leader,
+   * false if not.
+   * @async
+   */
   applyOnce: function applyOnce() {
     var _this2 = this;
 
@@ -423,82 +445,113 @@ LeaderElection.prototype = {
     }
 
     if (this.isDead) {
-      return _util.PROMISE_RESOLVED_FALSE;
-    } // do nothing if already running
+      return (0, _util.sleep)(0, false);
+    }
+    /**
+     * Already applying more then once,
+     * -> wait for the apply queue to be finished.
+     */
 
 
-    if (this._isApl) {
-      this._reApply = true;
-      return (0, _util.sleep)(0, false);
+    if (this._aplQC > 1) {
+      return this._aplQ;
     }
+    /**
+     * Add a new apply-run
+     */
 
-    var stopCriteria = false;
-    var recieved = [];
 
-    var handleMessage = function handleMessage(msg) {
-      if (msg.context === 'leader' && msg.token != _this2.token) {
-        recieved.push(msg);
+    var applyRun = function applyRun() {
+      /**
+       * Optimization shortcuts.
+       * Directly return if a previous run
+       * has already elected a leader.
+       */
+      if (_this2.isLeader) {
+        return _util.PROMISE_RESOLVED_TRUE;
+      }
 
-        if (msg.action === 'apply') {
-          // other is applying
-          if (msg.token > _this2.token) {
-            // other has higher token, stop applying
-            stopCriteria = true;
-          }
-        }
+      var stopCriteria = false;
+      var stopCriteriaPromiseResolve;
+      /**
+       * Resolves when a stop criteria is reached.
+       * Uses as a performance shortcut so we do not
+       * have to await the responseTime when it is already clear
+       * that the election failed.
+       */
 
-        if (msg.action === 'tell') {
-          // other is already leader
+      var stopCriteriaPromise = new Promise(function (res) {
+        stopCriteriaPromiseResolve = function stopCriteriaPromiseResolve() {
           stopCriteria = true;
-          _this2.hasLeader = true;
+          res();
+        };
+      });
+      var recieved = [];
+
+      var handleMessage = function handleMessage(msg) {
+        if (msg.context === 'leader' && msg.token != _this2.token) {
+          recieved.push(msg);
+
+          if (msg.action === 'apply') {
+            // other is applying
+            if (msg.token > _this2.token) {
+              /**
+               * other has higher token
+               * -> stop applying and let other become leader.
+               */
+              stopCriteriaPromiseResolve();
+            }
+          }
+
+          if (msg.action === 'tell') {
+            // other is already leader
+            stopCriteriaPromiseResolve();
+            _this2.hasLeader = true;
+          }
         }
-      }
-    };
+      };
 
-    this.broadcastChannel.addEventListener('internal', handleMessage);
+      _this2.broadcastChannel.addEventListener('internal', handleMessage);
 
-    var applyPromise = _sendMessage(this, 'apply') // send out that this one is applying
-    .then(function () {
-      return (0, _util.sleep)(_this2._options.responseTime);
-    }) // let others time to respond
-    .then(function () {
-      if (stopCriteria) {
-        return Promise.reject(new Error());
-      } else {
+      var applyPromise = _sendMessage(_this2, 'apply') // send out that this one is applying
+      .then(function () {
+        return Promise.race([(0, _util.sleep)(_this2._options.responseTime / 2), stopCriteriaPromise.then(function () {
+          return Promise.reject(new Error());
+        })]);
+      }) // send again in case another instance was just created
+      .then(function () {
         return _sendMessage(_this2, 'apply');
-      }
-    }).then(function () {
-      return (0, _util.sleep)(_this2._options.responseTime);
-    }) // let others time to respond
-    .then(function () {
-      if (stopCriteria) {
-        return Promise.reject(new Error());
-      } else {
-        return _sendMessage(_this2);
-      }
-    }).then(function () {
-      return beLeader(_this2);
-    }) // no one disagreed -> this one is now leader
-    .then(function () {
-      return true;
-    })["catch"](function () {
-      return false;
-    }) // apply not successfull
-    .then(function (success) {
-      _this2.broadcastChannel.removeEventListener('internal', handleMessage);
+      }) // let others time to respond
+      .then(function () {
+        return Promise.race([(0, _util.sleep)(_this2._options.responseTime / 2), stopCriteriaPromise.then(function () {
+          return Promise.reject(new Error());
+        })]);
+      })["catch"](function () {}).then(function () {
+        _this2.broadcastChannel.removeEventListener('internal', handleMessage);
+
+        if (!stopCriteria) {
+          // no stop criteria -> own is leader
+          return beLeader(_this2).then(function () {
+            return true;
+          });
+        } else {
+          // other is leader
+          return false;
+        }
+      });
 
-      _this2._isApl = false;
+      return applyPromise;
+    };
 
-      if (!success && _this2._reApply) {
-        _this2._reApply = false;
-        return _this2.applyOnce();
-      } else {
-        return success;
-      }
+    this._aplQC = this._aplQC + 1;
+    this._aplQ = this._aplQ.then(function () {
+      return applyRun();
+    }).then(function () {
+      _this2._aplQC = _this2._aplQC - 1;
+    });
+    return this._aplQ.then(function () {
+      return _this2.isLeader;
     });
-
-    this._isApl = applyPromise;
-    return applyPromise;
   },
   awaitLeadership: function awaitLeadership() {
     if (
@@ -575,6 +628,7 @@ function _awaitLeadershipOnce(leaderElector) {
     }); // try on fallbackInterval
 
     var interval = setInterval(function () {
+      console.log('applyOnce via fallbackInterval');
       leaderElector.applyOnce().then(function () {
         if (leaderElector.isLeader) {
           finish();
@@ -1510,7 +1564,7 @@ function fillOptionsWithDefaults() {
 Object.defineProperty(exports, "__esModule", {
   value: true
 });
-exports.isNode = exports.PROMISE_RESOLVED_VOID = exports.PROMISE_RESOLVED_FALSE = void 0;
+exports.isNode = exports.PROMISE_RESOLVED_VOID = exports.PROMISE_RESOLVED_TRUE = exports.PROMISE_RESOLVED_FALSE = void 0;
 exports.isPromise = isPromise;
 exports.microSeconds = microSeconds;
 exports.randomInt = randomInt;
@@ -1530,6 +1584,8 @@ function isPromise(obj) {
 
 var PROMISE_RESOLVED_FALSE = Promise.resolve(false);
 exports.PROMISE_RESOLVED_FALSE = PROMISE_RESOLVED_FALSE;
+var PROMISE_RESOLVED_TRUE = Promise.resolve(true);
+exports.PROMISE_RESOLVED_TRUE = PROMISE_RESOLVED_TRUE;
 var PROMISE_RESOLVED_VOID = Promise.resolve();
 exports.PROMISE_RESOLVED_VOID = PROMISE_RESOLVED_VOID;
 
diff --git a/dist/lib/browser.min.js b/dist/lib/browser.min.js
index 0e1ab23f..13b802fa 100644
--- a/dist/lib/browser.min.js
+++ b/dist/lib/browser.min.js
@@ -1 +1 @@
-!function r(o,i,s){function a(t,e){if(!i[t]){if(!o[t]){var n="function"==typeof require&&require;if(!e&&n)return n(t,!0);if(u)return u(t,!0);throw(n=new Error("Cannot find module '"+t+"'")).code="MODULE_NOT_FOUND",n}n=i[t]={exports:{}},o[t][0].call(n.exports,function(e){return a(o[t][1][e]||e)},n,n.exports,r,o,i,s)}return i[t].exports}for(var u="function"==typeof require&&require,e=0;e<s.length;e++)a(s[e]);return a}({1:[function(e,t,n){"use strict";Object.defineProperty(n,"__esModule",{value:!0}),n.BroadcastChannel=void 0,n.clearNodeFolder=function(e){e=(0,s.fillOptionsWithDefaults)(e);e=(0,i.chooseMethod)(e);return"node"===e.type?e.clearNodeFolder().then(function(){return!0}):o.PROMISE_RESOLVED_FALSE},n.enforceOptions=function(e){r=e};var r,o=e("./util.js"),i=e("./method-chooser.js"),s=e("./options.js"),e=function(e,t){var n;this.name=e,r&&(t=r),this.options=(0,s.fillOptionsWithDefaults)(t),this.method=(0,i.chooseMethod)(this.options),this._iL=!1,this._onML=null,this._addEL={message:[],internal:[]},this._uMP=new Set,this._befC=[],this._prepP=null,t=(n=this).method.create(n.name,n.options),(0,o.isPromise)(t)?(n._prepP=t).then(function(e){n._state=e}):n._state=t};function a(t,e,n){var r={time:t.method.microSeconds(),type:e,data:n};return(t._prepP||o.PROMISE_RESOLVED_VOID).then(function(){var e=t.method.postMessage(t._state,r);return t._uMP.add(e),e.catch().then(function(){return t._uMP.delete(e)}),e})}function u(e){return 0<e._addEL.message.length||0<e._addEL.internal.length}function c(e,t,n){e._addEL[t].push(n),function(e){{var t,n;!e._iL&&u(e)&&(t=function(t){e._addEL[t.type].forEach(function(e){t.time>=e.time&&e.fn(t.data)})},n=e.method.microSeconds(),e._prepP?e._prepP.then(function(){e._iL=!0,e.method.onMessage(e._state,t,n)}):(e._iL=!0,e.method.onMessage(e._state,t,n)))}}(e)}function l(e,t,n){e._addEL[t]=e._addEL[t].filter(function(e){return e!==n}),function(e){{var t;e._iL&&!u(e)&&(e._iL=!1,t=e.method.microSeconds(),e.method.onMessage(e._state,null,t))}}(e)}(n.BroadcastChannel=e)._pubkey=!0,e.prototype={postMessage:function(e){if(this.closed)throw new Error("BroadcastChannel.postMessage(): Cannot post message after channel has closed");return a(this,"message",e)},postInternal:function(e){return a(this,"internal",e)},set onmessage(e){var t={time:this.method.microSeconds(),fn:e};l(this,"message",this._onML),e&&"function"==typeof e?(this._onML=t,c(this,"message",t)):this._onML=null},addEventListener:function(e,t){var n=this.method.microSeconds();c(this,e,{time:n,fn:t})},removeEventListener:function(e,t){var n=this._addEL[e].find(function(e){return e.fn===t});l(this,e,n)},close:function(){var e=this;if(!this.closed){this.closed=!0;var t=this._prepP||o.PROMISE_RESOLVED_VOID;return this._onML=null,this._addEL.message=[],t.then(function(){return Promise.all(Array.from(e._uMP))}).then(function(){return Promise.all(e._befC.map(function(e){return e()}))}).then(function(){return e.method.close(e._state)})}},get type(){return this.method.type},get isClosed(){return this.closed}}},{"./method-chooser.js":6,"./options.js":11,"./util.js":12}],2:[function(e,t,n){"use strict";var r=e("./index.es5.js"),e=r.BroadcastChannel,r=r.createLeaderElection;window.BroadcastChannel2=e,window.createLeaderElection=r},{"./index.es5.js":3}],3:[function(e,t,n){"use strict";e=e("./index.js");t.exports={BroadcastChannel:e.BroadcastChannel,createLeaderElection:e.createLeaderElection,clearNodeFolder:e.clearNodeFolder,enforceOptions:e.enforceOptions,beLeader:e.beLeader}},{"./index.js":4}],4:[function(e,t,n){"use strict";Object.defineProperty(n,"__esModule",{value:!0}),Object.defineProperty(n,"BroadcastChannel",{enumerable:!0,get:function(){return r.BroadcastChannel}}),Object.defineProperty(n,"beLeader",{enumerable:!0,get:function(){return 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clearTimeout?clearTimeout:s}catch(e){o=s}}();var u,c=[],l=!1,d=-1;function f(){l&&u&&(l=!1,u.length?c=u.concat(c):d=-1,c.length&&h())}function h(){if(!l){var e=a(f);l=!0;for(var t=c.length;t;){for(u=c,c=[];++d<t;)u&&u[d].run();d=-1,t=c.length}u=null,l=!1,function(t){if(o===clearTimeout)return clearTimeout(t);if((o===s||!o)&&clearTimeout)return o=clearTimeout,clearTimeout(t);try{o(t)}catch(e){try{return o.call(null,t)}catch(e){return o.call(this,t)}}}(e)}}function p(e,t){this.fun=e,this.array=t}function m(){}t.nextTick=function(e){var t=new Array(arguments.length-1);if(1<arguments.length)for(var n=1;n<arguments.length;n++)t[n-1]=arguments[n];c.push(new p(e,t)),1!==c.length||l||a(h)},p.prototype.run=function(){this.fun.apply(null,this.array)},t.title="browser",t.browser=!0,t.env={},t.argv=[],t.version="",t.versions={},t.on=m,t.addListener=m,t.once=m,t.off=m,t.removeListener=m,t.removeAllListeners=m,t.emit=m,t.prependListener=m,t.prependOnceListener=m,t.listeners=function(e){return[]},t.binding=function(e){throw new Error("process.binding is not supported")},t.cwd=function(){return"/"},t.chdir=function(e){throw new Error("process.chdir is not supported")},t.umask=function(){return 0}},{}],19:[function(e,t,n){"use strict";Object.defineProperty(n,"__esModule",{value:!0}),n.default=void 0,n.default={add:function(e){"function"==typeof WorkerGlobalScope&&self instanceof WorkerGlobalScope||"function"==typeof window.addEventListener&&(window.addEventListener("beforeunload",function(){e()},!0),window.addEventListener("unload",function(){e()},!0))}}},{}],20:[function(e,t,n){"use strict";var r=e("@babel/runtime/helpers/interopRequireDefault");Object.defineProperty(n,"__esModule",{value:!0}),n.add=function(e){if(a||(a=!0,i.add(u)),"function"!=typeof e)throw new Error("Listener is no function");return s.add(e),{remove:function(){return s.delete(e)},run:function(){return s.delete(e),e()}}},n.getSize=function(){return s.size},n.removeAll=function(){s.clear()},n.runAll=u;var o=r(e("detect-node")),n=r(e("./browser.js")),e=r(e("./node.js")),i=(o.default?e:n).default,s=new Set,a=!1;function u(){var t=[];return s.forEach(function(e){t.push(e()),s.delete(e)}),Promise.all(t)}},{"./browser.js":19,"./node.js":15,"@babel/runtime/helpers/interopRequireDefault":13,"detect-node":16}]},{},[2]);
\ No newline at end of file
diff --git a/dist/lib/index.js b/dist/lib/index.js
index 8bc266af..f02b5343 100644
--- a/dist/lib/index.js
+++ b/dist/lib/index.js
@@ -9,6 +9,12 @@ Object.defineProperty(exports, "BroadcastChannel", {
     return _broadcastChannel.BroadcastChannel;
   }
 });
+Object.defineProperty(exports, "OPEN_BROADCAST_CHANNELS", {
+  enumerable: true,
+  get: function get() {
+    return _broadcastChannel.OPEN_BROADCAST_CHANNELS;
+  }
+});
 Object.defineProperty(exports, "beLeader", {
   enumerable: true,
   get: function get() {
diff --git a/dist/lib/leader-election.js b/dist/lib/leader-election.js
index 86fe742c..31424cb0 100644
--- a/dist/lib/leader-election.js
+++ b/dist/lib/leader-election.js
@@ -20,15 +20,14 @@ var LeaderElection = function LeaderElection(broadcastChannel, options) {
   this.isDead = false;
   this.token = (0, _util.randomToken)();
   /**
-   * _isApplying
-   * Only set when a leader application is
-   * running at the moment.
-   * @type {Promise<any> | null}
+   * Apply Queue,
+   * used to ensure we do not run applyOnce()
+   * in parallel.
    */
 
-  this._isApl = false; // _isApplying
+  this._aplQ = _util.PROMISE_RESOLVED_VOID; // amount of unfinished applyOnce() calls
 
-  this._reApply = false; // things to clean up
+  this._aplQC = 0; // things to clean up
 
   this._unl = []; // _unloads
 
@@ -65,6 +64,11 @@ var LeaderElection = function LeaderElection(broadcastChannel, options) {
 };
 
 LeaderElection.prototype = {
+  /**
+   * Returns true if the instance is leader,
+   * false if not.
+   * @async
+   */
   applyOnce: function applyOnce() {
     var _this2 = this;
 
@@ -73,82 +77,113 @@ LeaderElection.prototype = {
     }
 
     if (this.isDead) {
-      return _util.PROMISE_RESOLVED_FALSE;
-    } // do nothing if already running
+      return (0, _util.sleep)(0, false);
+    }
+    /**
+     * Already applying more then once,
+     * -> wait for the apply queue to be finished.
+     */
 
 
-    if (this._isApl) {
-      this._reApply = true;
-      return (0, _util.sleep)(0, false);
+    if (this._aplQC > 1) {
+      return this._aplQ;
     }
+    /**
+     * Add a new apply-run
+     */
 
-    var stopCriteria = false;
-    var recieved = [];
 
-    var handleMessage = function handleMessage(msg) {
-      if (msg.context === 'leader' && msg.token != _this2.token) {
-        recieved.push(msg);
+    var applyRun = function applyRun() {
+      /**
+       * Optimization shortcuts.
+       * Directly return if a previous run
+       * has already elected a leader.
+       */
+      if (_this2.isLeader) {
+        return _util.PROMISE_RESOLVED_TRUE;
+      }
 
-        if (msg.action === 'apply') {
-          // other is applying
-          if (msg.token > _this2.token) {
-            // other has higher token, stop applying
-            stopCriteria = true;
-          }
-        }
+      var stopCriteria = false;
+      var stopCriteriaPromiseResolve;
+      /**
+       * Resolves when a stop criteria is reached.
+       * Uses as a performance shortcut so we do not
+       * have to await the responseTime when it is already clear
+       * that the election failed.
+       */
 
-        if (msg.action === 'tell') {
-          // other is already leader
+      var stopCriteriaPromise = new Promise(function (res) {
+        stopCriteriaPromiseResolve = function stopCriteriaPromiseResolve() {
           stopCriteria = true;
-          _this2.hasLeader = true;
+          res();
+        };
+      });
+      var recieved = [];
+
+      var handleMessage = function handleMessage(msg) {
+        if (msg.context === 'leader' && msg.token != _this2.token) {
+          recieved.push(msg);
+
+          if (msg.action === 'apply') {
+            // other is applying
+            if (msg.token > _this2.token) {
+              /**
+               * other has higher token
+               * -> stop applying and let other become leader.
+               */
+              stopCriteriaPromiseResolve();
+            }
+          }
+
+          if (msg.action === 'tell') {
+            // other is already leader
+            stopCriteriaPromiseResolve();
+            _this2.hasLeader = true;
+          }
         }
-      }
-    };
+      };
 
-    this.broadcastChannel.addEventListener('internal', handleMessage);
+      _this2.broadcastChannel.addEventListener('internal', handleMessage);
 
-    var applyPromise = _sendMessage(this, 'apply') // send out that this one is applying
-    .then(function () {
-      return (0, _util.sleep)(_this2._options.responseTime);
-    }) // let others time to respond
-    .then(function () {
-      if (stopCriteria) {
-        return Promise.reject(new Error());
-      } else {
+      var applyPromise = _sendMessage(_this2, 'apply') // send out that this one is applying
+      .then(function () {
+        return Promise.race([(0, _util.sleep)(_this2._options.responseTime / 2), stopCriteriaPromise.then(function () {
+          return Promise.reject(new Error());
+        })]);
+      }) // send again in case another instance was just created
+      .then(function () {
         return _sendMessage(_this2, 'apply');
-      }
-    }).then(function () {
-      return (0, _util.sleep)(_this2._options.responseTime);
-    }) // let others time to respond
-    .then(function () {
-      if (stopCriteria) {
-        return Promise.reject(new Error());
-      } else {
-        return _sendMessage(_this2);
-      }
+      }) // let others time to respond
+      .then(function () {
+        return Promise.race([(0, _util.sleep)(_this2._options.responseTime / 2), stopCriteriaPromise.then(function () {
+          return Promise.reject(new Error());
+        })]);
+      })["catch"](function () {}).then(function () {
+        _this2.broadcastChannel.removeEventListener('internal', handleMessage);
+
+        if (!stopCriteria) {
+          // no stop criteria -> own is leader
+          return beLeader(_this2).then(function () {
+            return true;
+          });
+        } else {
+          // other is leader
+          return false;
+        }
+      });
+
+      return applyPromise;
+    };
+
+    this._aplQC = this._aplQC + 1;
+    this._aplQ = this._aplQ.then(function () {
+      return applyRun();
     }).then(function () {
-      return beLeader(_this2);
-    }) // no one disagreed -> this one is now leader
-    .then(function () {
-      return true;
-    })["catch"](function () {
-      return false;
-    }) // apply not successfull
-    .then(function (success) {
-      _this2.broadcastChannel.removeEventListener('internal', handleMessage);
-
-      _this2._isApl = false;
-
-      if (!success && _this2._reApply) {
-        _this2._reApply = false;
-        return _this2.applyOnce();
-      } else {
-        return success;
-      }
+      _this2._aplQC = _this2._aplQC - 1;
+    });
+    return this._aplQ.then(function () {
+      return _this2.isLeader;
     });
-
-    this._isApl = applyPromise;
-    return applyPromise;
   },
   awaitLeadership: function awaitLeadership() {
     if (
@@ -225,6 +260,7 @@ function _awaitLeadershipOnce(leaderElector) {
     }); // try on fallbackInterval
 
     var interval = setInterval(function () {
+      console.log('applyOnce via fallbackInterval');
       leaderElector.applyOnce().then(function () {
         if (leaderElector.isLeader) {
           finish();
diff --git a/dist/lib/methods/node.js b/dist/lib/methods/node.js
index 3a0f716b..4c142626 100644
--- a/dist/lib/methods/node.js
+++ b/dist/lib/methods/node.js
@@ -1066,7 +1066,10 @@ function postMessage(channelState, messageJson) {
 
 
 function emitOverFastPath(state, msgObj, messageJson) {
-  if (!state.options.node.useFastPath) return; // disabled
+  if (!state.options.node.useFastPath) {
+    // disabled
+    return;
+  }
 
   var others = OTHER_INSTANCES[state.channelName].filter(function (s) {
     return s !== state;
diff --git a/dist/lib/util.js b/dist/lib/util.js
index 1afac5ba..c70aec48 100644
--- a/dist/lib/util.js
+++ b/dist/lib/util.js
@@ -3,7 +3,7 @@
 Object.defineProperty(exports, "__esModule", {
   value: true
 });
-exports.isNode = exports.PROMISE_RESOLVED_VOID = exports.PROMISE_RESOLVED_FALSE = void 0;
+exports.isNode = exports.PROMISE_RESOLVED_VOID = exports.PROMISE_RESOLVED_TRUE = exports.PROMISE_RESOLVED_FALSE = void 0;
 exports.isPromise = isPromise;
 exports.microSeconds = microSeconds;
 exports.randomInt = randomInt;
@@ -23,6 +23,8 @@ function isPromise(obj) {
 
 var PROMISE_RESOLVED_FALSE = Promise.resolve(false);
 exports.PROMISE_RESOLVED_FALSE = PROMISE_RESOLVED_FALSE;
+var PROMISE_RESOLVED_TRUE = Promise.resolve(true);
+exports.PROMISE_RESOLVED_TRUE = PROMISE_RESOLVED_TRUE;
 var PROMISE_RESOLVED_VOID = Promise.resolve();
 exports.PROMISE_RESOLVED_VOID = PROMISE_RESOLVED_VOID;
 
diff --git a/docs/e2e.js b/docs/e2e.js
index 567210c8..1964ca43 100644
--- a/docs/e2e.js
+++ b/docs/e2e.js
@@ -4,7 +4,7 @@
 Object.defineProperty(exports, "__esModule", {
   value: true
 });
-exports.BroadcastChannel = void 0;
+exports.OPEN_BROADCAST_CHANNELS = exports.BroadcastChannel = void 0;
 exports.clearNodeFolder = clearNodeFolder;
 exports.enforceOptions = enforceOptions;
 
@@ -14,7 +14,18 @@ var _methodChooser = require("./method-chooser.js");
 
 var _options = require("./options.js");
 
+/**
+ * Contains all open channels,
+ * used in tests to ensure everything is closed.
+ */
+var OPEN_BROADCAST_CHANNELS = new Set();
+exports.OPEN_BROADCAST_CHANNELS = OPEN_BROADCAST_CHANNELS;
+var lastId = 0;
+
 var BroadcastChannel = function BroadcastChannel(name, options) {
+  // identifier of the channel to debug stuff
+  this.id = lastId++;
+  OPEN_BROADCAST_CHANNELS.add(this);
   this.name = name;
 
   if (ENFORCED_OPTIONS) {
@@ -155,6 +166,7 @@ BroadcastChannel.prototype = {
       return;
     }
 
+    OPEN_BROADCAST_CHANNELS["delete"](this);
     this.closed = true;
     var awaitPrepare = this._prepP ? this._prepP : _util.PROMISE_RESOLVED_VOID;
     this._onML = null;
@@ -310,6 +322,12 @@ Object.defineProperty(exports, "BroadcastChannel", {
     return _broadcastChannel.BroadcastChannel;
   }
 });
+Object.defineProperty(exports, "OPEN_BROADCAST_CHANNELS", {
+  enumerable: true,
+  get: function get() {
+    return _broadcastChannel.OPEN_BROADCAST_CHANNELS;
+  }
+});
 Object.defineProperty(exports, "beLeader", {
   enumerable: true,
   get: function get() {
@@ -361,15 +379,14 @@ var LeaderElection = function LeaderElection(broadcastChannel, options) {
   this.isDead = false;
   this.token = (0, _util.randomToken)();
   /**
-   * _isApplying
-   * Only set when a leader application is
-   * running at the moment.
-   * @type {Promise<any> | null}
+   * Apply Queue,
+   * used to ensure we do not run applyOnce()
+   * in parallel.
    */
 
-  this._isApl = false; // _isApplying
+  this._aplQ = _util.PROMISE_RESOLVED_VOID; // amount of unfinished applyOnce() calls
 
-  this._reApply = false; // things to clean up
+  this._aplQC = 0; // things to clean up
 
   this._unl = []; // _unloads
 
@@ -406,6 +423,11 @@ var LeaderElection = function LeaderElection(broadcastChannel, options) {
 };
 
 LeaderElection.prototype = {
+  /**
+   * Returns true if the instance is leader,
+   * false if not.
+   * @async
+   */
   applyOnce: function applyOnce() {
     var _this2 = this;
 
@@ -414,82 +436,113 @@ LeaderElection.prototype = {
     }
 
     if (this.isDead) {
-      return _util.PROMISE_RESOLVED_FALSE;
-    } // do nothing if already running
+      return (0, _util.sleep)(0, false);
+    }
+    /**
+     * Already applying more then once,
+     * -> wait for the apply queue to be finished.
+     */
 
 
-    if (this._isApl) {
-      this._reApply = true;
-      return (0, _util.sleep)(0, false);
+    if (this._aplQC > 1) {
+      return this._aplQ;
     }
+    /**
+     * Add a new apply-run
+     */
 
-    var stopCriteria = false;
-    var recieved = [];
 
-    var handleMessage = function handleMessage(msg) {
-      if (msg.context === 'leader' && msg.token != _this2.token) {
-        recieved.push(msg);
+    var applyRun = function applyRun() {
+      /**
+       * Optimization shortcuts.
+       * Directly return if a previous run
+       * has already elected a leader.
+       */
+      if (_this2.isLeader) {
+        return _util.PROMISE_RESOLVED_TRUE;
+      }
 
-        if (msg.action === 'apply') {
-          // other is applying
-          if (msg.token > _this2.token) {
-            // other has higher token, stop applying
-            stopCriteria = true;
-          }
-        }
+      var stopCriteria = false;
+      var stopCriteriaPromiseResolve;
+      /**
+       * Resolves when a stop criteria is reached.
+       * Uses as a performance shortcut so we do not
+       * have to await the responseTime when it is already clear
+       * that the election failed.
+       */
 
-        if (msg.action === 'tell') {
-          // other is already leader
+      var stopCriteriaPromise = new Promise(function (res) {
+        stopCriteriaPromiseResolve = function stopCriteriaPromiseResolve() {
           stopCriteria = true;
-          _this2.hasLeader = true;
+          res();
+        };
+      });
+      var recieved = [];
+
+      var handleMessage = function handleMessage(msg) {
+        if (msg.context === 'leader' && msg.token != _this2.token) {
+          recieved.push(msg);
+
+          if (msg.action === 'apply') {
+            // other is applying
+            if (msg.token > _this2.token) {
+              /**
+               * other has higher token
+               * -> stop applying and let other become leader.
+               */
+              stopCriteriaPromiseResolve();
+            }
+          }
+
+          if (msg.action === 'tell') {
+            // other is already leader
+            stopCriteriaPromiseResolve();
+            _this2.hasLeader = true;
+          }
         }
-      }
-    };
+      };
 
-    this.broadcastChannel.addEventListener('internal', handleMessage);
+      _this2.broadcastChannel.addEventListener('internal', handleMessage);
 
-    var applyPromise = _sendMessage(this, 'apply') // send out that this one is applying
-    .then(function () {
-      return (0, _util.sleep)(_this2._options.responseTime);
-    }) // let others time to respond
-    .then(function () {
-      if (stopCriteria) {
-        return Promise.reject(new Error());
-      } else {
+      var applyPromise = _sendMessage(_this2, 'apply') // send out that this one is applying
+      .then(function () {
+        return Promise.race([(0, _util.sleep)(_this2._options.responseTime / 2), stopCriteriaPromise.then(function () {
+          return Promise.reject(new Error());
+        })]);
+      }) // send again in case another instance was just created
+      .then(function () {
         return _sendMessage(_this2, 'apply');
-      }
-    }).then(function () {
-      return (0, _util.sleep)(_this2._options.responseTime);
-    }) // let others time to respond
-    .then(function () {
-      if (stopCriteria) {
-        return Promise.reject(new Error());
-      } else {
-        return _sendMessage(_this2);
-      }
-    }).then(function () {
-      return beLeader(_this2);
-    }) // no one disagreed -> this one is now leader
-    .then(function () {
-      return true;
-    })["catch"](function () {
-      return false;
-    }) // apply not successfull
-    .then(function (success) {
-      _this2.broadcastChannel.removeEventListener('internal', handleMessage);
+      }) // let others time to respond
+      .then(function () {
+        return Promise.race([(0, _util.sleep)(_this2._options.responseTime / 2), stopCriteriaPromise.then(function () {
+          return Promise.reject(new Error());
+        })]);
+      })["catch"](function () {}).then(function () {
+        _this2.broadcastChannel.removeEventListener('internal', handleMessage);
+
+        if (!stopCriteria) {
+          // no stop criteria -> own is leader
+          return beLeader(_this2).then(function () {
+            return true;
+          });
+        } else {
+          // other is leader
+          return false;
+        }
+      });
 
-      _this2._isApl = false;
+      return applyPromise;
+    };
 
-      if (!success && _this2._reApply) {
-        _this2._reApply = false;
-        return _this2.applyOnce();
-      } else {
-        return success;
-      }
+    this._aplQC = this._aplQC + 1;
+    this._aplQ = this._aplQ.then(function () {
+      return applyRun();
+    }).then(function () {
+      _this2._aplQC = _this2._aplQC - 1;
+    });
+    return this._aplQ.then(function () {
+      return _this2.isLeader;
     });
-
-    this._isApl = applyPromise;
-    return applyPromise;
   },
   awaitLeadership: function awaitLeadership() {
     if (
@@ -566,6 +619,7 @@ function _awaitLeadershipOnce(leaderElector) {
     }); // try on fallbackInterval
 
     var interval = setInterval(function () {
+      console.log('applyOnce via fallbackInterval');
       leaderElector.applyOnce().then(function () {
         if (leaderElector.isLeader) {
           finish();
@@ -1501,7 +1555,7 @@ function fillOptionsWithDefaults() {
 Object.defineProperty(exports, "__esModule", {
   value: true
 });
-exports.isNode = exports.PROMISE_RESOLVED_VOID = exports.PROMISE_RESOLVED_FALSE = void 0;
+exports.isNode = exports.PROMISE_RESOLVED_VOID = exports.PROMISE_RESOLVED_TRUE = exports.PROMISE_RESOLVED_FALSE = void 0;
 exports.isPromise = isPromise;
 exports.microSeconds = microSeconds;
 exports.randomInt = randomInt;
@@ -1521,6 +1575,8 @@ function isPromise(obj) {
 
 var PROMISE_RESOLVED_FALSE = Promise.resolve(false);
 exports.PROMISE_RESOLVED_FALSE = PROMISE_RESOLVED_FALSE;
+var PROMISE_RESOLVED_TRUE = Promise.resolve(true);
+exports.PROMISE_RESOLVED_TRUE = PROMISE_RESOLVED_TRUE;
 var PROMISE_RESOLVED_VOID = Promise.resolve();
 exports.PROMISE_RESOLVED_VOID = PROMISE_RESOLVED_VOID;
 
diff --git a/docs/iframe.js b/docs/iframe.js
index e7693790..11d0b6de 100644
--- a/docs/iframe.js
+++ b/docs/iframe.js
@@ -4,7 +4,7 @@
 Object.defineProperty(exports, "__esModule", {
   value: true
 });
-exports.BroadcastChannel = void 0;
+exports.OPEN_BROADCAST_CHANNELS = exports.BroadcastChannel = void 0;
 exports.clearNodeFolder = clearNodeFolder;
 exports.enforceOptions = enforceOptions;
 
@@ -14,7 +14,18 @@ var _methodChooser = require("./method-chooser.js");
 
 var _options = require("./options.js");
 
+/**
+ * Contains all open channels,
+ * used in tests to ensure everything is closed.
+ */
+var OPEN_BROADCAST_CHANNELS = new Set();
+exports.OPEN_BROADCAST_CHANNELS = OPEN_BROADCAST_CHANNELS;
+var lastId = 0;
+
 var BroadcastChannel = function BroadcastChannel(name, options) {
+  // identifier of the channel to debug stuff
+  this.id = lastId++;
+  OPEN_BROADCAST_CHANNELS.add(this);
   this.name = name;
 
   if (ENFORCED_OPTIONS) {
@@ -155,6 +166,7 @@ BroadcastChannel.prototype = {
       return;
     }
 
+    OPEN_BROADCAST_CHANNELS["delete"](this);
     this.closed = true;
     var awaitPrepare = this._prepP ? this._prepP : _util.PROMISE_RESOLVED_VOID;
     this._onML = null;
@@ -310,6 +322,12 @@ Object.defineProperty(exports, "BroadcastChannel", {
     return _broadcastChannel.BroadcastChannel;
   }
 });
+Object.defineProperty(exports, "OPEN_BROADCAST_CHANNELS", {
+  enumerable: true,
+  get: function get() {
+    return _broadcastChannel.OPEN_BROADCAST_CHANNELS;
+  }
+});
 Object.defineProperty(exports, "beLeader", {
   enumerable: true,
   get: function get() {
@@ -361,15 +379,14 @@ var LeaderElection = function LeaderElection(broadcastChannel, options) {
   this.isDead = false;
   this.token = (0, _util.randomToken)();
   /**
-   * _isApplying
-   * Only set when a leader application is
-   * running at the moment.
-   * @type {Promise<any> | null}
+   * Apply Queue,
+   * used to ensure we do not run applyOnce()
+   * in parallel.
    */
 
-  this._isApl = false; // _isApplying
+  this._aplQ = _util.PROMISE_RESOLVED_VOID; // amount of unfinished applyOnce() calls
 
-  this._reApply = false; // things to clean up
+  this._aplQC = 0; // things to clean up
 
   this._unl = []; // _unloads
 
@@ -406,6 +423,11 @@ var LeaderElection = function LeaderElection(broadcastChannel, options) {
 };
 
 LeaderElection.prototype = {
+  /**
+   * Returns true if the instance is leader,
+   * false if not.
+   * @async
+   */
   applyOnce: function applyOnce() {
     var _this2 = this;
 
@@ -414,82 +436,113 @@ LeaderElection.prototype = {
     }
 
     if (this.isDead) {
-      return _util.PROMISE_RESOLVED_FALSE;
-    } // do nothing if already running
+      return (0, _util.sleep)(0, false);
+    }
+    /**
+     * Already applying more then once,
+     * -> wait for the apply queue to be finished.
+     */
 
 
-    if (this._isApl) {
-      this._reApply = true;
-      return (0, _util.sleep)(0, false);
+    if (this._aplQC > 1) {
+      return this._aplQ;
     }
+    /**
+     * Add a new apply-run
+     */
 
-    var stopCriteria = false;
-    var recieved = [];
 
-    var handleMessage = function handleMessage(msg) {
-      if (msg.context === 'leader' && msg.token != _this2.token) {
-        recieved.push(msg);
+    var applyRun = function applyRun() {
+      /**
+       * Optimization shortcuts.
+       * Directly return if a previous run
+       * has already elected a leader.
+       */
+      if (_this2.isLeader) {
+        return _util.PROMISE_RESOLVED_TRUE;
+      }
 
-        if (msg.action === 'apply') {
-          // other is applying
-          if (msg.token > _this2.token) {
-            // other has higher token, stop applying
-            stopCriteria = true;
-          }
-        }
+      var stopCriteria = false;
+      var stopCriteriaPromiseResolve;
+      /**
+       * Resolves when a stop criteria is reached.
+       * Uses as a performance shortcut so we do not
+       * have to await the responseTime when it is already clear
+       * that the election failed.
+       */
 
-        if (msg.action === 'tell') {
-          // other is already leader
+      var stopCriteriaPromise = new Promise(function (res) {
+        stopCriteriaPromiseResolve = function stopCriteriaPromiseResolve() {
           stopCriteria = true;
-          _this2.hasLeader = true;
+          res();
+        };
+      });
+      var recieved = [];
+
+      var handleMessage = function handleMessage(msg) {
+        if (msg.context === 'leader' && msg.token != _this2.token) {
+          recieved.push(msg);
+
+          if (msg.action === 'apply') {
+            // other is applying
+            if (msg.token > _this2.token) {
+              /**
+               * other has higher token
+               * -> stop applying and let other become leader.
+               */
+              stopCriteriaPromiseResolve();
+            }
+          }
+
+          if (msg.action === 'tell') {
+            // other is already leader
+            stopCriteriaPromiseResolve();
+            _this2.hasLeader = true;
+          }
         }
-      }
-    };
+      };
 
-    this.broadcastChannel.addEventListener('internal', handleMessage);
+      _this2.broadcastChannel.addEventListener('internal', handleMessage);
 
-    var applyPromise = _sendMessage(this, 'apply') // send out that this one is applying
-    .then(function () {
-      return (0, _util.sleep)(_this2._options.responseTime);
-    }) // let others time to respond
-    .then(function () {
-      if (stopCriteria) {
-        return Promise.reject(new Error());
-      } else {
+      var applyPromise = _sendMessage(_this2, 'apply') // send out that this one is applying
+      .then(function () {
+        return Promise.race([(0, _util.sleep)(_this2._options.responseTime / 2), stopCriteriaPromise.then(function () {
+          return Promise.reject(new Error());
+        })]);
+      }) // send again in case another instance was just created
+      .then(function () {
         return _sendMessage(_this2, 'apply');
-      }
-    }).then(function () {
-      return (0, _util.sleep)(_this2._options.responseTime);
-    }) // let others time to respond
-    .then(function () {
-      if (stopCriteria) {
-        return Promise.reject(new Error());
-      } else {
-        return _sendMessage(_this2);
-      }
-    }).then(function () {
-      return beLeader(_this2);
-    }) // no one disagreed -> this one is now leader
-    .then(function () {
-      return true;
-    })["catch"](function () {
-      return false;
-    }) // apply not successfull
-    .then(function (success) {
-      _this2.broadcastChannel.removeEventListener('internal', handleMessage);
+      }) // let others time to respond
+      .then(function () {
+        return Promise.race([(0, _util.sleep)(_this2._options.responseTime / 2), stopCriteriaPromise.then(function () {
+          return Promise.reject(new Error());
+        })]);
+      })["catch"](function () {}).then(function () {
+        _this2.broadcastChannel.removeEventListener('internal', handleMessage);
+
+        if (!stopCriteria) {
+          // no stop criteria -> own is leader
+          return beLeader(_this2).then(function () {
+            return true;
+          });
+        } else {
+          // other is leader
+          return false;
+        }
+      });
 
-      _this2._isApl = false;
+      return applyPromise;
+    };
 
-      if (!success && _this2._reApply) {
-        _this2._reApply = false;
-        return _this2.applyOnce();
-      } else {
-        return success;
-      }
+    this._aplQC = this._aplQC + 1;
+    this._aplQ = this._aplQ.then(function () {
+      return applyRun();
+    }).then(function () {
+      _this2._aplQC = _this2._aplQC - 1;
+    });
+    return this._aplQ.then(function () {
+      return _this2.isLeader;
     });
-
-    this._isApl = applyPromise;
-    return applyPromise;
   },
   awaitLeadership: function awaitLeadership() {
     if (
@@ -566,6 +619,7 @@ function _awaitLeadershipOnce(leaderElector) {
     }); // try on fallbackInterval
 
     var interval = setInterval(function () {
+      console.log('applyOnce via fallbackInterval');
       leaderElector.applyOnce().then(function () {
         if (leaderElector.isLeader) {
           finish();
@@ -1501,7 +1555,7 @@ function fillOptionsWithDefaults() {
 Object.defineProperty(exports, "__esModule", {
   value: true
 });
-exports.isNode = exports.PROMISE_RESOLVED_VOID = exports.PROMISE_RESOLVED_FALSE = void 0;
+exports.isNode = exports.PROMISE_RESOLVED_VOID = exports.PROMISE_RESOLVED_TRUE = exports.PROMISE_RESOLVED_FALSE = void 0;
 exports.isPromise = isPromise;
 exports.microSeconds = microSeconds;
 exports.randomInt = randomInt;
@@ -1521,6 +1575,8 @@ function isPromise(obj) {
 
 var PROMISE_RESOLVED_FALSE = Promise.resolve(false);
 exports.PROMISE_RESOLVED_FALSE = PROMISE_RESOLVED_FALSE;
+var PROMISE_RESOLVED_TRUE = Promise.resolve(true);
+exports.PROMISE_RESOLVED_TRUE = PROMISE_RESOLVED_TRUE;
 var PROMISE_RESOLVED_VOID = Promise.resolve();
 exports.PROMISE_RESOLVED_VOID = PROMISE_RESOLVED_VOID;
 
diff --git a/docs/index.js b/docs/index.js
index ec721460..3dc1eb4c 100644
--- a/docs/index.js
+++ b/docs/index.js
@@ -4,7 +4,7 @@
 Object.defineProperty(exports, "__esModule", {
   value: true
 });
-exports.BroadcastChannel = void 0;
+exports.OPEN_BROADCAST_CHANNELS = exports.BroadcastChannel = void 0;
 exports.clearNodeFolder = clearNodeFolder;
 exports.enforceOptions = enforceOptions;
 
@@ -14,7 +14,18 @@ var _methodChooser = require("./method-chooser.js");
 
 var _options = require("./options.js");
 
+/**
+ * Contains all open channels,
+ * used in tests to ensure everything is closed.
+ */
+var OPEN_BROADCAST_CHANNELS = new Set();
+exports.OPEN_BROADCAST_CHANNELS = OPEN_BROADCAST_CHANNELS;
+var lastId = 0;
+
 var BroadcastChannel = function BroadcastChannel(name, options) {
+  // identifier of the channel to debug stuff
+  this.id = lastId++;
+  OPEN_BROADCAST_CHANNELS.add(this);
   this.name = name;
 
   if (ENFORCED_OPTIONS) {
@@ -155,6 +166,7 @@ BroadcastChannel.prototype = {
       return;
     }
 
+    OPEN_BROADCAST_CHANNELS["delete"](this);
     this.closed = true;
     var awaitPrepare = this._prepP ? this._prepP : _util.PROMISE_RESOLVED_VOID;
     this._onML = null;
@@ -310,6 +322,12 @@ Object.defineProperty(exports, "BroadcastChannel", {
     return _broadcastChannel.BroadcastChannel;
   }
 });
+Object.defineProperty(exports, "OPEN_BROADCAST_CHANNELS", {
+  enumerable: true,
+  get: function get() {
+    return _broadcastChannel.OPEN_BROADCAST_CHANNELS;
+  }
+});
 Object.defineProperty(exports, "beLeader", {
   enumerable: true,
   get: function get() {
@@ -361,15 +379,14 @@ var LeaderElection = function LeaderElection(broadcastChannel, options) {
   this.isDead = false;
   this.token = (0, _util.randomToken)();
   /**
-   * _isApplying
-   * Only set when a leader application is
-   * running at the moment.
-   * @type {Promise<any> | null}
+   * Apply Queue,
+   * used to ensure we do not run applyOnce()
+   * in parallel.
    */
 
-  this._isApl = false; // _isApplying
+  this._aplQ = _util.PROMISE_RESOLVED_VOID; // amount of unfinished applyOnce() calls
 
-  this._reApply = false; // things to clean up
+  this._aplQC = 0; // things to clean up
 
   this._unl = []; // _unloads
 
@@ -406,6 +423,11 @@ var LeaderElection = function LeaderElection(broadcastChannel, options) {
 };
 
 LeaderElection.prototype = {
+  /**
+   * Returns true if the instance is leader,
+   * false if not.
+   * @async
+   */
   applyOnce: function applyOnce() {
     var _this2 = this;
 
@@ -414,82 +436,113 @@ LeaderElection.prototype = {
     }
 
     if (this.isDead) {
-      return _util.PROMISE_RESOLVED_FALSE;
-    } // do nothing if already running
+      return (0, _util.sleep)(0, false);
+    }
+    /**
+     * Already applying more then once,
+     * -> wait for the apply queue to be finished.
+     */
 
 
-    if (this._isApl) {
-      this._reApply = true;
-      return (0, _util.sleep)(0, false);
+    if (this._aplQC > 1) {
+      return this._aplQ;
     }
+    /**
+     * Add a new apply-run
+     */
 
-    var stopCriteria = false;
-    var recieved = [];
 
-    var handleMessage = function handleMessage(msg) {
-      if (msg.context === 'leader' && msg.token != _this2.token) {
-        recieved.push(msg);
+    var applyRun = function applyRun() {
+      /**
+       * Optimization shortcuts.
+       * Directly return if a previous run
+       * has already elected a leader.
+       */
+      if (_this2.isLeader) {
+        return _util.PROMISE_RESOLVED_TRUE;
+      }
 
-        if (msg.action === 'apply') {
-          // other is applying
-          if (msg.token > _this2.token) {
-            // other has higher token, stop applying
-            stopCriteria = true;
-          }
-        }
+      var stopCriteria = false;
+      var stopCriteriaPromiseResolve;
+      /**
+       * Resolves when a stop criteria is reached.
+       * Uses as a performance shortcut so we do not
+       * have to await the responseTime when it is already clear
+       * that the election failed.
+       */
 
-        if (msg.action === 'tell') {
-          // other is already leader
+      var stopCriteriaPromise = new Promise(function (res) {
+        stopCriteriaPromiseResolve = function stopCriteriaPromiseResolve() {
           stopCriteria = true;
-          _this2.hasLeader = true;
+          res();
+        };
+      });
+      var recieved = [];
+
+      var handleMessage = function handleMessage(msg) {
+        if (msg.context === 'leader' && msg.token != _this2.token) {
+          recieved.push(msg);
+
+          if (msg.action === 'apply') {
+            // other is applying
+            if (msg.token > _this2.token) {
+              /**
+               * other has higher token
+               * -> stop applying and let other become leader.
+               */
+              stopCriteriaPromiseResolve();
+            }
+          }
+
+          if (msg.action === 'tell') {
+            // other is already leader
+            stopCriteriaPromiseResolve();
+            _this2.hasLeader = true;
+          }
         }
-      }
-    };
+      };
 
-    this.broadcastChannel.addEventListener('internal', handleMessage);
+      _this2.broadcastChannel.addEventListener('internal', handleMessage);
 
-    var applyPromise = _sendMessage(this, 'apply') // send out that this one is applying
-    .then(function () {
-      return (0, _util.sleep)(_this2._options.responseTime);
-    }) // let others time to respond
-    .then(function () {
-      if (stopCriteria) {
-        return Promise.reject(new Error());
-      } else {
+      var applyPromise = _sendMessage(_this2, 'apply') // send out that this one is applying
+      .then(function () {
+        return Promise.race([(0, _util.sleep)(_this2._options.responseTime / 2), stopCriteriaPromise.then(function () {
+          return Promise.reject(new Error());
+        })]);
+      }) // send again in case another instance was just created
+      .then(function () {
         return _sendMessage(_this2, 'apply');
-      }
-    }).then(function () {
-      return (0, _util.sleep)(_this2._options.responseTime);
-    }) // let others time to respond
-    .then(function () {
-      if (stopCriteria) {
-        return Promise.reject(new Error());
-      } else {
-        return _sendMessage(_this2);
-      }
-    }).then(function () {
-      return beLeader(_this2);
-    }) // no one disagreed -> this one is now leader
-    .then(function () {
-      return true;
-    })["catch"](function () {
-      return false;
-    }) // apply not successfull
-    .then(function (success) {
-      _this2.broadcastChannel.removeEventListener('internal', handleMessage);
+      }) // let others time to respond
+      .then(function () {
+        return Promise.race([(0, _util.sleep)(_this2._options.responseTime / 2), stopCriteriaPromise.then(function () {
+          return Promise.reject(new Error());
+        })]);
+      })["catch"](function () {}).then(function () {
+        _this2.broadcastChannel.removeEventListener('internal', handleMessage);
+
+        if (!stopCriteria) {
+          // no stop criteria -> own is leader
+          return beLeader(_this2).then(function () {
+            return true;
+          });
+        } else {
+          // other is leader
+          return false;
+        }
+      });
 
-      _this2._isApl = false;
+      return applyPromise;
+    };
 
-      if (!success && _this2._reApply) {
-        _this2._reApply = false;
-        return _this2.applyOnce();
-      } else {
-        return success;
-      }
+    this._aplQC = this._aplQC + 1;
+    this._aplQ = this._aplQ.then(function () {
+      return applyRun();
+    }).then(function () {
+      _this2._aplQC = _this2._aplQC - 1;
+    });
+    return this._aplQ.then(function () {
+      return _this2.isLeader;
     });
-
-    this._isApl = applyPromise;
-    return applyPromise;
   },
   awaitLeadership: function awaitLeadership() {
     if (
@@ -566,6 +619,7 @@ function _awaitLeadershipOnce(leaderElector) {
     }); // try on fallbackInterval
 
     var interval = setInterval(function () {
+      console.log('applyOnce via fallbackInterval');
       leaderElector.applyOnce().then(function () {
         if (leaderElector.isLeader) {
           finish();
@@ -1501,7 +1555,7 @@ function fillOptionsWithDefaults() {
 Object.defineProperty(exports, "__esModule", {
   value: true
 });
-exports.isNode = exports.PROMISE_RESOLVED_VOID = exports.PROMISE_RESOLVED_FALSE = void 0;
+exports.isNode = exports.PROMISE_RESOLVED_VOID = exports.PROMISE_RESOLVED_TRUE = exports.PROMISE_RESOLVED_FALSE = void 0;
 exports.isPromise = isPromise;
 exports.microSeconds = microSeconds;
 exports.randomInt = randomInt;
@@ -1521,6 +1575,8 @@ function isPromise(obj) {
 
 var PROMISE_RESOLVED_FALSE = Promise.resolve(false);
 exports.PROMISE_RESOLVED_FALSE = PROMISE_RESOLVED_FALSE;
+var PROMISE_RESOLVED_TRUE = Promise.resolve(true);
+exports.PROMISE_RESOLVED_TRUE = PROMISE_RESOLVED_TRUE;
 var PROMISE_RESOLVED_VOID = Promise.resolve();
 exports.PROMISE_RESOLVED_VOID = PROMISE_RESOLVED_VOID;
 
diff --git a/docs/leader-iframe.js b/docs/leader-iframe.js
index d481046f..6b60c269 100644
--- a/docs/leader-iframe.js
+++ b/docs/leader-iframe.js
@@ -4,7 +4,7 @@
 Object.defineProperty(exports, "__esModule", {
   value: true
 });
-exports.BroadcastChannel = void 0;
+exports.OPEN_BROADCAST_CHANNELS = exports.BroadcastChannel = void 0;
 exports.clearNodeFolder = clearNodeFolder;
 exports.enforceOptions = enforceOptions;
 
@@ -14,7 +14,18 @@ var _methodChooser = require("./method-chooser.js");
 
 var _options = require("./options.js");
 
+/**
+ * Contains all open channels,
+ * used in tests to ensure everything is closed.
+ */
+var OPEN_BROADCAST_CHANNELS = new Set();
+exports.OPEN_BROADCAST_CHANNELS = OPEN_BROADCAST_CHANNELS;
+var lastId = 0;
+
 var BroadcastChannel = function BroadcastChannel(name, options) {
+  // identifier of the channel to debug stuff
+  this.id = lastId++;
+  OPEN_BROADCAST_CHANNELS.add(this);
   this.name = name;
 
   if (ENFORCED_OPTIONS) {
@@ -155,6 +166,7 @@ BroadcastChannel.prototype = {
       return;
     }
 
+    OPEN_BROADCAST_CHANNELS["delete"](this);
     this.closed = true;
     var awaitPrepare = this._prepP ? this._prepP : _util.PROMISE_RESOLVED_VOID;
     this._onML = null;
@@ -310,6 +322,12 @@ Object.defineProperty(exports, "BroadcastChannel", {
     return _broadcastChannel.BroadcastChannel;
   }
 });
+Object.defineProperty(exports, "OPEN_BROADCAST_CHANNELS", {
+  enumerable: true,
+  get: function get() {
+    return _broadcastChannel.OPEN_BROADCAST_CHANNELS;
+  }
+});
 Object.defineProperty(exports, "beLeader", {
   enumerable: true,
   get: function get() {
@@ -361,15 +379,14 @@ var LeaderElection = function LeaderElection(broadcastChannel, options) {
   this.isDead = false;
   this.token = (0, _util.randomToken)();
   /**
-   * _isApplying
-   * Only set when a leader application is
-   * running at the moment.
-   * @type {Promise<any> | null}
+   * Apply Queue,
+   * used to ensure we do not run applyOnce()
+   * in parallel.
    */
 
-  this._isApl = false; // _isApplying
+  this._aplQ = _util.PROMISE_RESOLVED_VOID; // amount of unfinished applyOnce() calls
 
-  this._reApply = false; // things to clean up
+  this._aplQC = 0; // things to clean up
 
   this._unl = []; // _unloads
 
@@ -406,6 +423,11 @@ var LeaderElection = function LeaderElection(broadcastChannel, options) {
 };
 
 LeaderElection.prototype = {
+  /**
+   * Returns true if the instance is leader,
+   * false if not.
+   * @async
+   */
   applyOnce: function applyOnce() {
     var _this2 = this;
 
@@ -414,82 +436,113 @@ LeaderElection.prototype = {
     }
 
     if (this.isDead) {
-      return _util.PROMISE_RESOLVED_FALSE;
-    } // do nothing if already running
+      return (0, _util.sleep)(0, false);
+    }
+    /**
+     * Already applying more then once,
+     * -> wait for the apply queue to be finished.
+     */
 
 
-    if (this._isApl) {
-      this._reApply = true;
-      return (0, _util.sleep)(0, false);
+    if (this._aplQC > 1) {
+      return this._aplQ;
     }
+    /**
+     * Add a new apply-run
+     */
 
-    var stopCriteria = false;
-    var recieved = [];
 
-    var handleMessage = function handleMessage(msg) {
-      if (msg.context === 'leader' && msg.token != _this2.token) {
-        recieved.push(msg);
+    var applyRun = function applyRun() {
+      /**
+       * Optimization shortcuts.
+       * Directly return if a previous run
+       * has already elected a leader.
+       */
+      if (_this2.isLeader) {
+        return _util.PROMISE_RESOLVED_TRUE;
+      }
 
-        if (msg.action === 'apply') {
-          // other is applying
-          if (msg.token > _this2.token) {
-            // other has higher token, stop applying
-            stopCriteria = true;
-          }
-        }
+      var stopCriteria = false;
+      var stopCriteriaPromiseResolve;
+      /**
+       * Resolves when a stop criteria is reached.
+       * Uses as a performance shortcut so we do not
+       * have to await the responseTime when it is already clear
+       * that the election failed.
+       */
 
-        if (msg.action === 'tell') {
-          // other is already leader
+      var stopCriteriaPromise = new Promise(function (res) {
+        stopCriteriaPromiseResolve = function stopCriteriaPromiseResolve() {
           stopCriteria = true;
-          _this2.hasLeader = true;
+          res();
+        };
+      });
+      var recieved = [];
+
+      var handleMessage = function handleMessage(msg) {
+        if (msg.context === 'leader' && msg.token != _this2.token) {
+          recieved.push(msg);
+
+          if (msg.action === 'apply') {
+            // other is applying
+            if (msg.token > _this2.token) {
+              /**
+               * other has higher token
+               * -> stop applying and let other become leader.
+               */
+              stopCriteriaPromiseResolve();
+            }
+          }
+
+          if (msg.action === 'tell') {
+            // other is already leader
+            stopCriteriaPromiseResolve();
+            _this2.hasLeader = true;
+          }
         }
-      }
-    };
+      };
 
-    this.broadcastChannel.addEventListener('internal', handleMessage);
+      _this2.broadcastChannel.addEventListener('internal', handleMessage);
 
-    var applyPromise = _sendMessage(this, 'apply') // send out that this one is applying
-    .then(function () {
-      return (0, _util.sleep)(_this2._options.responseTime);
-    }) // let others time to respond
-    .then(function () {
-      if (stopCriteria) {
-        return Promise.reject(new Error());
-      } else {
+      var applyPromise = _sendMessage(_this2, 'apply') // send out that this one is applying
+      .then(function () {
+        return Promise.race([(0, _util.sleep)(_this2._options.responseTime / 2), stopCriteriaPromise.then(function () {
+          return Promise.reject(new Error());
+        })]);
+      }) // send again in case another instance was just created
+      .then(function () {
         return _sendMessage(_this2, 'apply');
-      }
-    }).then(function () {
-      return (0, _util.sleep)(_this2._options.responseTime);
-    }) // let others time to respond
-    .then(function () {
-      if (stopCriteria) {
-        return Promise.reject(new Error());
-      } else {
-        return _sendMessage(_this2);
-      }
-    }).then(function () {
-      return beLeader(_this2);
-    }) // no one disagreed -> this one is now leader
-    .then(function () {
-      return true;
-    })["catch"](function () {
-      return false;
-    }) // apply not successfull
-    .then(function (success) {
-      _this2.broadcastChannel.removeEventListener('internal', handleMessage);
+      }) // let others time to respond
+      .then(function () {
+        return Promise.race([(0, _util.sleep)(_this2._options.responseTime / 2), stopCriteriaPromise.then(function () {
+          return Promise.reject(new Error());
+        })]);
+      })["catch"](function () {}).then(function () {
+        _this2.broadcastChannel.removeEventListener('internal', handleMessage);
+
+        if (!stopCriteria) {
+          // no stop criteria -> own is leader
+          return beLeader(_this2).then(function () {
+            return true;
+          });
+        } else {
+          // other is leader
+          return false;
+        }
+      });
 
-      _this2._isApl = false;
+      return applyPromise;
+    };
 
-      if (!success && _this2._reApply) {
-        _this2._reApply = false;
-        return _this2.applyOnce();
-      } else {
-        return success;
-      }
+    this._aplQC = this._aplQC + 1;
+    this._aplQ = this._aplQ.then(function () {
+      return applyRun();
+    }).then(function () {
+      _this2._aplQC = _this2._aplQC - 1;
+    });
+    return this._aplQ.then(function () {
+      return _this2.isLeader;
     });
-
-    this._isApl = applyPromise;
-    return applyPromise;
   },
   awaitLeadership: function awaitLeadership() {
     if (
@@ -566,6 +619,7 @@ function _awaitLeadershipOnce(leaderElector) {
     }); // try on fallbackInterval
 
     var interval = setInterval(function () {
+      console.log('applyOnce via fallbackInterval');
       leaderElector.applyOnce().then(function () {
         if (leaderElector.isLeader) {
           finish();
@@ -1501,7 +1555,7 @@ function fillOptionsWithDefaults() {
 Object.defineProperty(exports, "__esModule", {
   value: true
 });
-exports.isNode = exports.PROMISE_RESOLVED_VOID = exports.PROMISE_RESOLVED_FALSE = void 0;
+exports.isNode = exports.PROMISE_RESOLVED_VOID = exports.PROMISE_RESOLVED_TRUE = exports.PROMISE_RESOLVED_FALSE = void 0;
 exports.isPromise = isPromise;
 exports.microSeconds = microSeconds;
 exports.randomInt = randomInt;
@@ -1521,6 +1575,8 @@ function isPromise(obj) {
 
 var PROMISE_RESOLVED_FALSE = Promise.resolve(false);
 exports.PROMISE_RESOLVED_FALSE = PROMISE_RESOLVED_FALSE;
+var PROMISE_RESOLVED_TRUE = Promise.resolve(true);
+exports.PROMISE_RESOLVED_TRUE = PROMISE_RESOLVED_TRUE;
 var PROMISE_RESOLVED_VOID = Promise.resolve();
 exports.PROMISE_RESOLVED_VOID = PROMISE_RESOLVED_VOID;
 
diff --git a/docs/worker.js b/docs/worker.js
index 116912f7..6076532b 100644
--- a/docs/worker.js
+++ b/docs/worker.js
@@ -4,7 +4,7 @@
 Object.defineProperty(exports, "__esModule", {
   value: true
 });
-exports.BroadcastChannel = void 0;
+exports.OPEN_BROADCAST_CHANNELS = exports.BroadcastChannel = void 0;
 exports.clearNodeFolder = clearNodeFolder;
 exports.enforceOptions = enforceOptions;
 
@@ -14,7 +14,18 @@ var _methodChooser = require("./method-chooser.js");
 
 var _options = require("./options.js");
 
+/**
+ * Contains all open channels,
+ * used in tests to ensure everything is closed.
+ */
+var OPEN_BROADCAST_CHANNELS = new Set();
+exports.OPEN_BROADCAST_CHANNELS = OPEN_BROADCAST_CHANNELS;
+var lastId = 0;
+
 var BroadcastChannel = function BroadcastChannel(name, options) {
+  // identifier of the channel to debug stuff
+  this.id = lastId++;
+  OPEN_BROADCAST_CHANNELS.add(this);
   this.name = name;
 
   if (ENFORCED_OPTIONS) {
@@ -155,6 +166,7 @@ BroadcastChannel.prototype = {
       return;
     }
 
+    OPEN_BROADCAST_CHANNELS["delete"](this);
     this.closed = true;
     var awaitPrepare = this._prepP ? this._prepP : _util.PROMISE_RESOLVED_VOID;
     this._onML = null;
@@ -310,6 +322,12 @@ Object.defineProperty(exports, "BroadcastChannel", {
     return _broadcastChannel.BroadcastChannel;
   }
 });
+Object.defineProperty(exports, "OPEN_BROADCAST_CHANNELS", {
+  enumerable: true,
+  get: function get() {
+    return _broadcastChannel.OPEN_BROADCAST_CHANNELS;
+  }
+});
 Object.defineProperty(exports, "beLeader", {
   enumerable: true,
   get: function get() {
@@ -361,15 +379,14 @@ var LeaderElection = function LeaderElection(broadcastChannel, options) {
   this.isDead = false;
   this.token = (0, _util.randomToken)();
   /**
-   * _isApplying
-   * Only set when a leader application is
-   * running at the moment.
-   * @type {Promise<any> | null}
+   * Apply Queue,
+   * used to ensure we do not run applyOnce()
+   * in parallel.
    */
 
-  this._isApl = false; // _isApplying
+  this._aplQ = _util.PROMISE_RESOLVED_VOID; // amount of unfinished applyOnce() calls
 
-  this._reApply = false; // things to clean up
+  this._aplQC = 0; // things to clean up
 
   this._unl = []; // _unloads
 
@@ -406,6 +423,11 @@ var LeaderElection = function LeaderElection(broadcastChannel, options) {
 };
 
 LeaderElection.prototype = {
+  /**
+   * Returns true if the instance is leader,
+   * false if not.
+   * @async
+   */
   applyOnce: function applyOnce() {
     var _this2 = this;
 
@@ -414,82 +436,113 @@ LeaderElection.prototype = {
     }
 
     if (this.isDead) {
-      return _util.PROMISE_RESOLVED_FALSE;
-    } // do nothing if already running
+      return (0, _util.sleep)(0, false);
+    }
+    /**
+     * Already applying more then once,
+     * -> wait for the apply queue to be finished.
+     */
 
 
-    if (this._isApl) {
-      this._reApply = true;
-      return (0, _util.sleep)(0, false);
+    if (this._aplQC > 1) {
+      return this._aplQ;
     }
+    /**
+     * Add a new apply-run
+     */
 
-    var stopCriteria = false;
-    var recieved = [];
 
-    var handleMessage = function handleMessage(msg) {
-      if (msg.context === 'leader' && msg.token != _this2.token) {
-        recieved.push(msg);
+    var applyRun = function applyRun() {
+      /**
+       * Optimization shortcuts.
+       * Directly return if a previous run
+       * has already elected a leader.
+       */
+      if (_this2.isLeader) {
+        return _util.PROMISE_RESOLVED_TRUE;
+      }
 
-        if (msg.action === 'apply') {
-          // other is applying
-          if (msg.token > _this2.token) {
-            // other has higher token, stop applying
-            stopCriteria = true;
-          }
-        }
+      var stopCriteria = false;
+      var stopCriteriaPromiseResolve;
+      /**
+       * Resolves when a stop criteria is reached.
+       * Uses as a performance shortcut so we do not
+       * have to await the responseTime when it is already clear
+       * that the election failed.
+       */
 
-        if (msg.action === 'tell') {
-          // other is already leader
+      var stopCriteriaPromise = new Promise(function (res) {
+        stopCriteriaPromiseResolve = function stopCriteriaPromiseResolve() {
           stopCriteria = true;
-          _this2.hasLeader = true;
+          res();
+        };
+      });
+      var recieved = [];
+
+      var handleMessage = function handleMessage(msg) {
+        if (msg.context === 'leader' && msg.token != _this2.token) {
+          recieved.push(msg);
+
+          if (msg.action === 'apply') {
+            // other is applying
+            if (msg.token > _this2.token) {
+              /**
+               * other has higher token
+               * -> stop applying and let other become leader.
+               */
+              stopCriteriaPromiseResolve();
+            }
+          }
+
+          if (msg.action === 'tell') {
+            // other is already leader
+            stopCriteriaPromiseResolve();
+            _this2.hasLeader = true;
+          }
         }
-      }
-    };
+      };
 
-    this.broadcastChannel.addEventListener('internal', handleMessage);
+      _this2.broadcastChannel.addEventListener('internal', handleMessage);
 
-    var applyPromise = _sendMessage(this, 'apply') // send out that this one is applying
-    .then(function () {
-      return (0, _util.sleep)(_this2._options.responseTime);
-    }) // let others time to respond
-    .then(function () {
-      if (stopCriteria) {
-        return Promise.reject(new Error());
-      } else {
+      var applyPromise = _sendMessage(_this2, 'apply') // send out that this one is applying
+      .then(function () {
+        return Promise.race([(0, _util.sleep)(_this2._options.responseTime / 2), stopCriteriaPromise.then(function () {
+          return Promise.reject(new Error());
+        })]);
+      }) // send again in case another instance was just created
+      .then(function () {
         return _sendMessage(_this2, 'apply');
-      }
-    }).then(function () {
-      return (0, _util.sleep)(_this2._options.responseTime);
-    }) // let others time to respond
-    .then(function () {
-      if (stopCriteria) {
-        return Promise.reject(new Error());
-      } else {
-        return _sendMessage(_this2);
-      }
-    }).then(function () {
-      return beLeader(_this2);
-    }) // no one disagreed -> this one is now leader
-    .then(function () {
-      return true;
-    })["catch"](function () {
-      return false;
-    }) // apply not successfull
-    .then(function (success) {
-      _this2.broadcastChannel.removeEventListener('internal', handleMessage);
+      }) // let others time to respond
+      .then(function () {
+        return Promise.race([(0, _util.sleep)(_this2._options.responseTime / 2), stopCriteriaPromise.then(function () {
+          return Promise.reject(new Error());
+        })]);
+      })["catch"](function () {}).then(function () {
+        _this2.broadcastChannel.removeEventListener('internal', handleMessage);
+
+        if (!stopCriteria) {
+          // no stop criteria -> own is leader
+          return beLeader(_this2).then(function () {
+            return true;
+          });
+        } else {
+          // other is leader
+          return false;
+        }
+      });
 
-      _this2._isApl = false;
+      return applyPromise;
+    };
 
-      if (!success && _this2._reApply) {
-        _this2._reApply = false;
-        return _this2.applyOnce();
-      } else {
-        return success;
-      }
+    this._aplQC = this._aplQC + 1;
+    this._aplQ = this._aplQ.then(function () {
+      return applyRun();
+    }).then(function () {
+      _this2._aplQC = _this2._aplQC - 1;
+    });
+    return this._aplQ.then(function () {
+      return _this2.isLeader;
     });
-
-    this._isApl = applyPromise;
-    return applyPromise;
   },
   awaitLeadership: function awaitLeadership() {
     if (
@@ -566,6 +619,7 @@ function _awaitLeadershipOnce(leaderElector) {
     }); // try on fallbackInterval
 
     var interval = setInterval(function () {
+      console.log('applyOnce via fallbackInterval');
       leaderElector.applyOnce().then(function () {
         if (leaderElector.isLeader) {
           finish();
@@ -1501,7 +1555,7 @@ function fillOptionsWithDefaults() {
 Object.defineProperty(exports, "__esModule", {
   value: true
 });
-exports.isNode = exports.PROMISE_RESOLVED_VOID = exports.PROMISE_RESOLVED_FALSE = void 0;
+exports.isNode = exports.PROMISE_RESOLVED_VOID = exports.PROMISE_RESOLVED_TRUE = exports.PROMISE_RESOLVED_FALSE = void 0;
 exports.isPromise = isPromise;
 exports.microSeconds = microSeconds;
 exports.randomInt = randomInt;
@@ -1521,6 +1575,8 @@ function isPromise(obj) {
 
 var PROMISE_RESOLVED_FALSE = Promise.resolve(false);
 exports.PROMISE_RESOLVED_FALSE = PROMISE_RESOLVED_FALSE;
+var PROMISE_RESOLVED_TRUE = Promise.resolve(true);
+exports.PROMISE_RESOLVED_TRUE = PROMISE_RESOLVED_TRUE;
 var PROMISE_RESOLVED_VOID = Promise.resolve();
 exports.PROMISE_RESOLVED_VOID = PROMISE_RESOLVED_VOID;