def test_works(self):
with open(self.path, 'w') as f:
json.dump({'A': 'a'}, f)
r = file_reader.FileReaderThread(self.path, 0.1)
r.start()
try:
self.assertEqual(r.last_value, {'A': 'a'})
# Change the file. Expect possible conflict on Windows.
attempt = 0
bytes_json = json.dumps({'B': 'b'}).encode('utf-8')
while True:
try:
file_path.atomic_replace(self.path, bytes_json)
break
except OSError:
attempt += 1
if attempt == 20:
self.fail('Cannot replace the file, giving up')
time.sleep(0.05)
# Give some reasonable time for the reader thread to pick up the change.
# This test will flake if for whatever reason OS thread scheduler is
# lagging for more than 2 seconds.
time.sleep(2)
self.assertEqual(r.last_value, {'B': 'b'})
finally:
r.stop()
def test_atomic_replace_existing_file(self):
path = os.path.join(self.tempdir, 'existing_file')
with open(path, 'wb') as f:
f.write('existing body')
file_path.atomic_replace(path, 'new body')
with open(path, 'rb') as f:
self.assertEqual('new body', f.read())
self.assertEqual([u'existing_file'], os.listdir(self.tempdir))
def _dump(self):
"""Attempts to rewrite the file, retrying a bunch of times.
Returns:
True to carry on, False to exit the thread.
"""
try:
blob = json.dumps(self._producer_callback(),
sort_keys=True,
indent=2,
separators=(',', ': '))
except Exception:
logging.exception('Unexpected exception in the callback')
return True
if blob == self._last_dumped_blob:
return True # already have it on disk
logging.info('Updating %s', self._path)
# On Windows the file may be locked by reading process. Don't freak out,
# just retry a bit later.
attempts = 100
while True:
try:
file_path.atomic_replace(self._path, blob)
self._last_dumped_blob = blob
return True # success!
except (IOError, OSError) as e:
logging.error('Failed to update the file: %s', e)
if not attempts:
logging.error(
'Failed to update the file %s after many attempts, giving up',
self._path)
return True
attempts -= 1
if not self._wait(0.05):
return False
def test_atomic_replace_new_file(self):
path = os.path.join(self.tempdir, 'new_file')
file_path.atomic_replace(path, 'blah')
with open(path, 'rb') as f:
self.assertEqual('blah', f.read())
self.assertEqual([u'new_file'], os.listdir(self.tempdir))