fix stackoverflows in queue when using synchronous tasks - WARNING, this slightly changes order of events when queue processing using sync tasks

2 files changed, 37 insertions, 11 deletions

diff --git a/lib/async.js b/lib/async.js
index 71903b3..7e8d2d0 100644
--- a/lib/async.js
+++ b/lib/async.js
@@ -706,7 +706,7 @@
                         data: task,
                         callback: typeof callback === 'function' ? callback : null
                     });
-                    if (q.saturated && q.tasks.length == concurrency) {
+                    if (q.saturated && q.tasks.length === concurrency) {
                         q.saturated();
                     }
                     async.nextTick(q.process);
@@ -715,16 +715,33 @@
             process: function () {
                 if (workers < q.concurrency && q.tasks.length) {
                     var task = q.tasks.shift();
-                    if(q.empty && q.tasks.length == 0) q.empty();
+                    if (q.empty && q.tasks.length === 0) {
+                        q.empty();
+                    }
                     workers += 1;
-                    worker(task.data, only_once(function() {
+                    var sync = true;
+                    var next = function () {
                         workers -= 1;
                         if (task.callback) {
                             task.callback.apply(task, arguments);
                         }
-                        if(q.drain && q.tasks.length + workers == 0) q.drain();
+                        if (q.drain && q.tasks.length + workers === 0) {
+                            q.drain();
+                        }
                         q.process();
-                    }));
+                    };
+                    var cb = only_once(function () {
+                        if (sync) {
+                            async.nextTick(function () {
+                                next.apply(null, arguments);
+                            });
+                        }
+                        else {
+                            next.apply(null, arguments);
+                        }
+                    });
+                    worker(task.data, cb);
+                    sync = false;
                 }
             },
             length: function () {
diff --git a/test/test-async.js b/test/test-async.js
index da6956a..956165d 100644
--- a/test/test-async.js
+++ b/test/test-async.js
@@ -2006,17 +2006,17 @@ exports['queue events'] = function(test) {
         test.same(calls, [
             'saturated',
             'process foo',
-            'foo cb',
             'process bar',
-            'bar cb',
             'process zoo',
-            'zoo cb',
+            'foo cb',
             'process poo',
-            'poo cb',
+            'bar cb',
             'empty',
             'process moo',
+            'zoo cb',
+            'poo cb',
             'moo cb',
-            'drain',
+            'drain'
         ]);
         test.done();
     };
@@ -2066,7 +2066,16 @@ exports['avoid stack overflows for sync tasks'] = function (test) {
         resetCounter,
         async.apply(async.doUntil, iter, pred2),
         async.apply(async.series, funcarr),
-        async.apply(async.parallel, funcarr)
+        async.apply(async.parallel, funcarr),
+        function (callback) {
+            var q = async.queue(function (task, cb) {
+                cb();
+            }, 2);
+            for (var j = 0; j < 10000; j++) {
+                q.push(j);
+            }
+            q.drain = callback;
+        }
     ],
     function (err) {
         test.done(err);