Split ResultList from Barrier so the barrier isn't modified by the ge…

…t_item() call

dpxdt/client/workers.py

@@ -112,7 +112,7 @@ def __init__(self, input_queue, output_queue):
             input_queue: Queue this worker consumes work from.
             output_queue: Queue where this worker puts new work items, if any.
         """
-        threading.Thread.__init__(self)
+        super(WorkerThread, self).__init__()
         self.daemon = True
         self.input_queue = input_queue
         self.output_queue = output_queue
@@ -189,7 +189,7 @@ class WorkflowItem(WorkItem):
     root = False
 
     def __init__(self, *args, **kwargs):
-        WorkItem.__init__(self)
+        super(WorkflowItem, self).__init__()
         self.args = args
         self.kwargs = kwargs
         self.interrupted = False
@@ -220,7 +220,23 @@ def __init__(self, items):
         self.items = items
 
 
-class Barrier(list):
+class ResultList(list):
+    """A list of results."""
+
+    @property
+    def error(self):
+        """Returns the error for this barrier and all work items, if any."""
+        # Copy the error from any failed item to be the error for the whole
+        # barrier. The first error seen "wins". Also handles the case where
+        # the WorkItems passed into the barrier have already completed and
+        # been marked with errors.
+        for item in self:
+            if isinstance(item, WorkItem) and item.error:
+                return item.error
+        return None
+
+
+class Barrier(ResultList):
     """Barrier for running multiple WorkItems in parallel."""
 
     def __init__(self, workflow, generator, work):
@@ -233,7 +249,7 @@ def __init__(self, workflow, generator, work):
                 a list or tuple that contains a set of WorkItems to run in
                 parallel.
         """
-        list.__init__(self)
+        super(Barrier, self).__init__()
         self.workflow = workflow
         self.generator = generator
 
@@ -278,31 +294,22 @@ def outstanding(self):
 
         return True
 
-    @property
-    def error(self):
-        """Returns the error for this barrier and all work items, if any."""
-        # Copy the error from any failed item to be the error for the whole
-        # barrier. The first error seen "wins". Also handles the case where
-        # the WorkItems passed into the barrier have already completed and
-        # been marked with errors.
-        for item in self:
-            if isinstance(item, WorkItem) and item.error:
-                return item.error
-        return None
-
     def get_item(self):
         """Returns the item to send back into the workflow generator."""
         if self.was_list:
-            blocking_items = self[:]
-            self[:] = []
-            for item in blocking_items:
-                if (isinstance(item, WorkflowItem) and
-                        item.done and
-                        not item.error):
-                    self.append(item.result)
+            result = ResultList()
+            for item in self:
+                if isinstance(item, WorkflowItem):
+                    if item.done and not item.error:
+                        result.append(item.result)
+                    else:
+                        # When there's an error or the workflow isn't done yet,
+                        # just return the original WorkflowItem so the caller
+                        # can inspect its entire state.
+                        result.append(item)
                 else:
-                    self.append(item)
-            return self
+                    result.append(item)
+            return result
         else:
             return self[0]
 
@@ -409,7 +416,7 @@ class using the register() method.
             output_queue: Queue where this worker puts finished work items,
                 if any.
         """
-        WorkerThread.__init__(self, input_queue, output_queue)
+        super(WorkflowThread, self).__init__(input_queue, output_queue)
         self.pending = PendingBarriers()
         self.worker_threads = []
         self.register(WorkflowItem, input_queue)