[SPARK-13697] [PYSPARK] Fix the missing module name of TransformFunctionSerializer.loads

## What changes were proposed in this pull request?

Set the function's module name to `__main__` if it's missing in `TransformFunctionSerializer.loads`.

## How was this patch tested?

Manually test in the shell.

Before this patch:
```
>>> from pyspark.streaming import StreamingContext
>>> from pyspark.streaming.util import TransformFunction
>>> ssc = StreamingContext(sc, 1)
>>> func = TransformFunction(sc, lambda x: x, sc.serializer)
>>> func.rdd_wrapper(lambda x: x)
TransformFunction(<function <lambda> at 0x106ac8b18>)
>>> bytes = bytearray(ssc._transformerSerializer.serializer.dumps((func.func, func.rdd_wrap_func, func.deserializers)))
>>> func2 = ssc._transformerSerializer.loads(bytes)
>>> print(func2.func.__module__)
None
>>> print(func2.rdd_wrap_func.__module__)
None
>>>
```
After this patch:
```
>>> from pyspark.streaming import StreamingContext
>>> from pyspark.streaming.util import TransformFunction
>>> ssc = StreamingContext(sc, 1)
>>> func = TransformFunction(sc, lambda x: x, sc.serializer)
>>> func.rdd_wrapper(lambda x: x)
TransformFunction(<function <lambda> at 0x108bf1b90>)
>>> bytes = bytearray(ssc._transformerSerializer.serializer.dumps((func.func, func.rdd_wrap_func, func.deserializers)))
>>> func2 = ssc._transformerSerializer.loads(bytes)
>>> print(func2.func.__module__)
__main__
>>> print(func2.rdd_wrap_func.__module__)
__main__
>>>
```

Author: Shixiong Zhu <[email protected]>

Closes #11535 from zsxwing/loads-module.

(cherry picked from commit ee913e6)
Signed-off-by: Davies Liu <[email protected]>

Author: zsxwing

python/pyspark/cloudpickle.py

@@ -241,6 +241,7 @@ def save_function_tuple(self, func):
         save(f_globals)
         save(defaults)
         save(dct)
+        save(func.__module__)
         write(pickle.TUPLE)
         write(pickle.REDUCE)  # applies _fill_function on the tuple
 
@@ -674,13 +675,14 @@ def _genpartial(func, args, kwds):
     return partial(func, *args, **kwds)
 
 
-def _fill_function(func, globals, defaults, dict):
+def _fill_function(func, globals, defaults, dict, module):
     """ Fills in the rest of function data into the skeleton function object
         that were created via _make_skel_func().
          """
     func.__globals__.update(globals)
     func.__defaults__ = defaults
     func.__dict__ = dict
+    func.__module__ = module
 
     return func
 

python/pyspark/tests.py

@@ -230,6 +230,12 @@ def test_itemgetter(self):
         getter2 = ser.loads(ser.dumps(getter))
         self.assertEqual(getter(d), getter2(d))
 
+    def test_function_module_name(self):
+        ser = CloudPickleSerializer()
+        func = lambda x: x
+        func2 = ser.loads(ser.dumps(func))
+        self.assertEqual(func.__module__, func2.__module__)
+
     def test_attrgetter(self):
         from operator import attrgetter
         ser = CloudPickleSerializer()