Add comment to why we accumulate before notifying task listeners.

1 files changed, 4 insertions, 0 deletions

diff --git a/taskflow/patterns/ordered_flow.py b/taskflow/patterns/ordered_flow.py
index 9b4bc08..5d20ec8 100644
--- a/taskflow/patterns/ordered_flow.py
+++ b/taskflow/patterns/ordered_flow.py
@@ -147,6 +147,10 @@ class Flow(object):
                 # if rollback occurs that the task gets exactly the
                 # result it returned and not a modified one.
                 self.results.append((task, result))
+                # Add the task result to the accumulator before
+                # notifying others that the task has finished to
+                # avoid the case where a listener might throw an
+                # exception.
                 self._accumulator.add(RollbackTask(context, task,
                                                    copy.deepcopy(result)))
                 self._on_task_finish(context, task, result)