Add reduce method to allow for pickling of Parallel table objects.

daskms/parallel_table.py

@@ -8,6 +8,11 @@
 log = logging.getLogger(__name__)
 
 
+def _map_create_parallel_table(cls, args, kwargs):
+    """ Support pickling of kwargs in ParallelTable.__reduce__ """
+    return cls(*args, **kwargs)
+
+
 def _parallel_table_finalizer(_linked_tables):
 
     for table in _linked_tables.values():
@@ -31,6 +36,13 @@ def __init__(self, *args, **kwargs):
 
         finalize(self, _parallel_table_finalizer, self._linked_tables)
 
+    def __reduce__(self):
+        """ Defer to _map_create_parallel_table to support kwarg pickling """
+        return (
+            _map_create_parallel_table,
+            (ParallelTable, self._args, self._kwargs)
+        )
+
     def getcol(self, *args, **kwargs):
         table = self._get_table(threading.get_ident())
         return table.getcol(*args, **kwargs)