diff --git a/python/pyspark/tests.py b/python/pyspark/tests.py
index bb13de563cdd..e1c5f007268a 100644
--- a/python/pyspark/tests.py
+++ b/python/pyspark/tests.py
@@ -1,3 +1,4 @@
+# coding=utf-8
 #
 # Licensed to the Apache Software Foundation (ASF) under one or more
 # contributor license agreements.  See the NOTICE file distributed with
@@ -1859,6 +1860,31 @@ def test_with_different_versions_of_python(self):
         finally:
             self.sc.pythonVer = version
 
+    def test_exception_blocking(self):
+        """
+        SPARK-21045
+        Test whether program is blocked when occur exception in worker sending
+        exception to PythonRDD
+
+        """
+        import threading
+
+        def run():
+            try:
+
+                def f():
+                    raise Exception("中")
+
+                self.sc.parallelize([1]).map(lambda x: f()).count()
+            except Exception:
+                pass
+
+        t = threading.Thread(target=run)
+        t.daemon = True
+        t.start()
+        t.join(10)
+        self.assertFalse(t.isAlive(), 'Spark executor is blocked.')
+
 
 class SparkSubmitTests(unittest.TestCase):
 
diff --git a/python/pyspark/worker.py b/python/pyspark/worker.py
index baaa3fe074e9..11c6555b1fdc 100644
--- a/python/pyspark/worker.py
+++ b/python/pyspark/worker.py
@@ -36,6 +36,9 @@
 pickleSer = PickleSerializer()
 utf8_deserializer = UTF8Deserializer()
 
+if sys.version >= '3':
+    unicode = str
+
 
 def report_times(outfile, boot, init, finish):
     write_int(SpecialLengths.TIMING_DATA, outfile)
@@ -177,8 +180,11 @@ def process():
             process()
     except Exception:
         try:
+            exc_info = traceback.format_exc()
+            if isinstance(exc_info, unicode):
+                exc_info = exc_info.encode('utf-8')
             write_int(SpecialLengths.PYTHON_EXCEPTION_THROWN, outfile)
-            write_with_length(traceback.format_exc().encode("utf-8"), outfile)
+            write_with_length(exc_info, outfile)
         except IOError:
             # JVM close the socket
             pass