2 files changed, 32 insertions, 21 deletions

diff --git a/lib/async.js b/lib/async.js
index 68b9c54..58b11d9 100644
--- a/lib/async.js
+++ b/lib/async.js
@@ -37,7 +37,16 @@
         return function() {
             if (called) throw new Error("Callback was already called.");
             called = true;
-            fn.apply(root, arguments);
+            fn.apply(this, arguments);
+        };
+    }
+
+    function _once(fn) {
+        var called = false;
+        return function() {
+            if (called) return;
+            called = true;
+            fn.apply(this, arguments);
         };
     }
 
@@ -206,7 +215,7 @@
 
     async.forEachOf =
     async.eachOf = function (object, iterator, callback) {
-        callback = callback || noop;
+        callback = _once(callback || noop);
         object = object || [];
         var size = object.length || _keys(object).length;
         var completed = 0;
@@ -219,7 +228,6 @@
         function done(err) {
           if (err) {
               callback(err);
-              callback = noop;
           }
           else {
               completed += 1;
@@ -232,7 +240,7 @@
 
     async.forEachOfSeries =
     async.eachOfSeries = function (obj, iterator, callback) {
-        callback = callback || noop;
+        callback = _once(callback || noop);
         obj = obj || [];
         var nextKey = _keyIterator(obj);
         function iterate() {
@@ -244,7 +252,6 @@
             iterator(obj[key], key, function (err) {
                 if (err) {
                     callback(err);
-                    callback = noop;
                 }
                 else {
                     if (sync) {
@@ -270,7 +277,7 @@
     function _eachOfLimit(limit) {
 
         return function (obj, iterator, callback) {
-            callback = callback || noop;
+            callback = _once(callback || noop);
             obj = obj || [];
             var nextKey = _keyIterator(obj);
             if (limit <= 0) {
@@ -282,9 +289,7 @@
 
             (function replenish () {
                 if (done && running <= 0) {
-                    callback(null);
-                    callback = noop;
-                    return;
+                    return callback(null);
                 }
 
                 while (running < limit && !errored) {
@@ -293,7 +298,6 @@
                         done = true;
                         if (running <= 0) {
                             callback(null);
-                            callback = noop;
                         }
                         return;
                     }
@@ -303,7 +307,6 @@
                         if (err) {
                             callback(err);
                             errored = true;
-                            callback = noop;
                         }
                         else {
                             replenish();
@@ -504,7 +507,7 @@
     };
 
     async.auto = function (tasks, callback) {
-        callback = callback || noop;
+        callback = _once(callback || noop);
         var keys = _keys(tasks);
         var remainingTasks = keys.length;
         if (!remainingTasks) {
@@ -534,11 +537,7 @@
 
         addListener(function () {
             if (!remainingTasks) {
-                var theCallback = callback;
-                // prevent final callback from calling itself if it errors
-                callback = noop;
-
-                theCallback(null, results);
+                callback(null, results);
             }
         });
 
@@ -556,8 +555,6 @@
                     });
                     safeResults[k] = args;
                     callback(err, safeResults);
-                    // stop subsequent errors hitting callback multiple times
-                    callback = noop;
                 }
                 else {
                     results[k] = args;
@@ -631,7 +628,7 @@
     };
 
     async.waterfall = function (tasks, callback) {
-        callback = callback || noop;
+        callback = _once(callback || noop);
         if (!_isArray(tasks)) {
           var err = new Error('First argument to waterfall must be an array of functions');
           return callback(err);
@@ -643,7 +640,6 @@
             return function (err) {
                 if (err) {
                     callback.apply(null, arguments);
-                    callback = noop;
                 }
                 else {
                     var args = _baseSlice(arguments, 1);
diff --git a/test/test-async.js b/test/test-async.js
index ce2fc8d..2fe11bd 100755
--- a/test/test-async.js
+++ b/test/test-async.js
@@ -596,6 +596,21 @@ exports['auto calls callback multiple times'] = function(test) {
     }, 10);
 };
 
+
+exports['auto calls callback multiple times with parallel functions'] = function(test) {
+    test.expect(1);
+    async.auto({
+        task1: function(callback) { setTimeout(callback,0,"err"); },
+        task2: function(callback) { setTimeout(callback,0,"err"); }
+    },
+    // Error throwing final callback. This should only run once
+    function(err) {
+        test.equal(err, "err");
+        test.done();
+    });
+};
+
+
 // Issue 462 on github: https://github.com/caolan/async/issues/462
 exports['auto modifying results causes final callback to run early'] = function(test) {
     async.auto({