Release greenthread when computing checksum

Having time.sleep(0) after reading each block of data for computing
checksum will allow other greenthreads to run.

Closes-Bug: 1882569
Change-Id: I6e547d206de9e3e333e29ccad52bf6b519a86ff9
(cherry picked from commit b9938230f9)
(cherry picked from commit eeb7b10107)

oslo_utils/fileutils.py

@@ -25,6 +25,7 @@ import hashlib
 import os
 import stat
 import tempfile
+import time
 
 from oslo_utils import excutils
 
@@ -123,6 +124,8 @@ def compute_file_checksum(path, read_chunksize=65536, algorithm='sha256'):
     with open(path, 'rb') as f:
         for chunk in iter(lambda: f.read(read_chunksize), b''):
             checksum.update(chunk)
+            # Release greenthread, if greenthreads are not used it is a noop.
+            time.sleep(0)
     return checksum.hexdigest()
 
 

oslo_utils/tests/test_fileutils.py

@@ -19,8 +19,10 @@ import os
 import shutil
 import stat
 import tempfile
+import time
 import uuid
 
+import mock
 from oslotest import base as test_base
 import six
 
@@ -215,6 +217,23 @@ class TestComputeFileChecksum(test_base.BaseTestCase):
 
         self.assertEqual(expected_checksum.hexdigest(), actual_checksum)
 
+    def test_compute_checksum_sleep_0_called(self):
+        path = fileutils.write_to_tempfile(self.content)
+        self.assertTrue(os.path.exists(path))
+        self.check_file_content(self.content, path)
+
+        expected_checksum = hashlib.sha256()
+        expected_checksum.update(self.content)
+
+        with mock.patch.object(time, "sleep") as sleep_mock:
+            actual_checksum = fileutils.compute_file_checksum(
+                path, read_chunksize=4)
+
+        sleep_mock.assert_has_calls([mock.call(0)] * 3)
+        # Just to make sure that there were exactly 3 calls
+        self.assertEqual(3, sleep_mock.call_count)
+        self.assertEqual(expected_checksum.hexdigest(), actual_checksum)
+
     def test_compute_checksum_named_algorithm(self):
         path = fileutils.write_to_tempfile(self.content)
         self.assertTrue(os.path.exists(path))