THRIFT-5454: add __setState__ function to TProcessPoolServer to enable correct multiprocessing behavior related to pickling

Client: Python

lib/py/src/server/TProcessPoolServer.py

@@ -42,6 +42,11 @@ class TProcessPoolServer(TServer):
         self.stopCondition = Condition()
         self.postForkCallback = None
 
+    def __getstate__(self):
+        state=self.__dict__.copy()
+        state['workers'] = None
+        return state
+
     def setPostForkCallback(self, callback):
         if not callable(callback):
             raise TypeError("This is not a callback!")