cleanup mmap files in unittest, test=develop (#22814)

python/paddle/fluid/tests/unittests/test_imperative_data_loader_process.py

@@ -14,6 +14,7 @@
 
 import sys
 import unittest
+import multiprocessing
 import numpy as np
 import paddle.fluid as fluid
 from paddle.fluid import core
@@ -50,6 +51,14 @@ class TestDygraphDataLoaderProcess(unittest.TestCase):
         self.capacity = 2
 
     def test_reader_process_loop(self):
+        # This unittest's memory mapped files needs to be cleaned manually
+        def __clear_process__(util_queue):
+            while True:
+                try:
+                    util_queue.get_nowait()
+                except queue.Empty:
+                    break
+
         with fluid.dygraph.guard():
             loader = fluid.io.DataLoader.from_generator(
                 capacity=self.batch_num + 1, use_multiprocess=True)
@@ -58,8 +67,16 @@ class TestDygraphDataLoaderProcess(unittest.TestCase):
                 places=fluid.CPUPlace())
             loader._data_queue = queue.Queue(self.batch_num + 1)
             loader._reader_process_loop()
+            # For clean memory mapped files
+            util_queue = multiprocessing.Queue(self.batch_num + 1)
             for _ in range(self.batch_num):
-                loader._data_queue.get(timeout=10)
+                data = loader._data_queue.get(timeout=10)
+                util_queue.put(data)
+
+            # Clean up memory mapped files
+            clear_process = multiprocessing.Process(
+                target=__clear_process__, args=(util_queue, ))
+            clear_process.start()
 
     def test_reader_process_loop_simple_none(self):
         def none_sample_genarator(batch_num):