Clear the stack if onmessage is called before the previous invocation finishes

spec/core/ClearStackSpec.js

@@ -37,6 +37,27 @@ describe("ClearStack", function() {
     expect(called).toBe(true);
   });
 
+  it("calls setTimeout when onmessage is called recursively", function() {
+    var fakeChannel = {
+          port1: {},
+          port2: { postMessage: function() { fakeChannel.port1.onmessage(); } }
+        },
+        setTimeout = jasmine.createSpy('setTimeout'),
+        global = {
+          MessageChannel: function() { return fakeChannel; },
+          setTimeout: setTimeout,
+        },
+        clearStack = jasmineUnderTest.getClearStack(global),
+        fn = jasmine.createSpy("second clearStack function");
+
+    clearStack(function() {
+      clearStack(fn);
+    });
+
+    expect(fn).not.toHaveBeenCalled();
+    expect(setTimeout).toHaveBeenCalledWith(fn, 0);
+  });
+
   it("falls back to setTimeout", function() {
     var setTimeout = jasmine.createSpy('setTimeout').and.callFake(function(fn) { fn() }),
         global = { setTimeout: setTimeout },

src/core/ClearStack.js

@@ -4,11 +4,22 @@ getJasmineRequireObj().clearStack = function(j$) {
         head = {},
         tail = head;
 
+    var taskRunning = false;
     channel.port1.onmessage = function() {
       head = head.next;
       var task = head.task;
       delete head.task;
-      task();
+
+      if (taskRunning) {
+        global.setTimeout(task, 0);
+      } else {
+        try {
+          taskRunning = true;
+          task();
+        } finally {
+          taskRunning = false;
+        }
+      }
     };
 
     return function clearStack(fn) {