Merge "Combine multiple exceptions into a linked one"

taskflow/exceptions.py

@@ -16,6 +16,10 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import StringIO
+
+import traceback
+
 
 class TaskFlowException(Exception):
     """Base class for exceptions emitted from this library."""
@@ -27,6 +31,33 @@ class Duplicate(TaskFlowException):
     pass
 
 
+class LinkedException(TaskFlowException):
+    """A linked chain of many exceptions."""
+    def __init__(self, message, cause, tb):
+        super(LinkedException, self).__init__(message)
+        self.cause = cause
+        self.tb = tb
+        self.next = None
+
+    @classmethod
+    def link(cls, exc_infos):
+        first = None
+        previous = None
+        for exc_info in exc_infos:
+            if not all(exc_info) or not len(exc_infos) == 3:
+                raise ValueError("Invalid exc_info")
+            buf = StringIO.StringIO()
+            traceback.print_exception(exc_info[0], exc_info[1], exc_info[2],
+                                      file=buf)
+            exc = cls(str(exc_info[1]), exc_info[1], buf.getvalue())
+            if previous is not None:
+                previous.next = exc
+            else:
+                first = exc
+            previous = exc
+        return first
+
+
 class StorageError(TaskFlowException):
     """Raised when logbook can not be read/saved/deleted."""
 

taskflow/patterns/threaded_flow.py

@@ -350,11 +350,12 @@ class Flow(flow.Flow):
             except exc.InvalidStateException:
                 pass
             finally:
-                # TODO(harlowja): re-raise a combined exception when
-                # there are more than one failures??
-                for f in failures:
-                    if all(f.exc_info):
-                        raise f.exc_info[0], f.exc_info[1], f.exc_info[2]
+                if len(failures) > 1:
+                    exc_infos = [f.exc_info for f in failures]
+                    raise exc.LinkedException.link(exc_infos)
+                else:
+                    f = failures[0]
+                    raise f.exc_info[0], f.exc_info[1], f.exc_info[2]
 
         def handle_results():
             # Isolate each runner state into groups so that we can easily tell