add a fake reader for speed test

python/paddle/reader/decorator.py

@@ -15,7 +15,7 @@
 __all__ = [
     'map_readers', 'buffered', 'compose', 'chain', 'shuffle',
     'ComposeNotAligned', 'firstn', 'xmap_readers', 'PipeReader',
-    'multiprocess_reader'
+    'multiprocess_reader', 'fake'
 ]
 
 from threading import Thread
@@ -504,3 +504,26 @@ class PipeReader:
                     yield decomp_buff
             else:
                 break
+
+
+def fake(reader, data_num):
+    """
+    fake reader will cache the first data it read and yield it out for data_num times.
+    It is used to cache a data from real reader and use it for speed testing.
+
+    :param reader: the origin reader
+    :param data_num: times that this reader will yield data.
+    :return: a fake reader.
+    """
+
+    def fake_reader():
+        if fake_reader.data is None:
+            fake_reader.data = reader().next()
+        while fake_reader.yield_num < data_num:
+            yield fake_reader.data
+            fake_reader.yield_num += 1
+
+    fake_reader.data = None
+    fake_reader.yield_num = 0
+
+    return fake_reader

python/paddle/reader/tests/decorator_test.py

@@ -203,5 +203,20 @@ class TestMultiProcessReader(unittest.TestCase):
         self.reader_test(use_pipe=True)
 
 
+class TestFakeReader(unittest.TestCase):
+    def test_fake_reader(self):
+        def reader():
+            for i in range(10):
+                yield i
+
+        data_num = 100
+        fake_reader = paddle.reader.fake(reader, data_num)
+        i = 0
+        for data in fake_reader():
+            self.assertEqual(data, 0)
+            i += 1
+        self.assertEqual(i, data_num)
+
+
 if __name__ == '__main__':
     unittest.main()