Send authorization headers when calling Swarming backend.

appengine/swarming/swarming_bot/bot_code/file_refresher.py

+# Copyright 2016 The LUCI Authors. All rights reserved.
+# Use of this source code is governed under the Apache License, Version 2.0
+# that can be found in the LICENSE file.
+
+import json
+import logging
+import Queue
+import threading
+import time
+
+from utils import file_path
+
+
+class FileRefresher(object):
+  """Represents a thread that periodically dumps result of a callback to a file.
+
+  Used by bot_main to send authnetication headers to task_runner. task_runner
+  reads them from the file when making HTTP calls.
+
+  Uses JSON for serialization. Doesn't delete the file when stopped.
+  """
+
+  def __init__(self, path, producer_callback, interval_sec=60):
+    self._path = path
+    self._producer_callback = producer_callback
+    self._interval_sec = interval_sec
+    self._thread = None
+    self._signal = None
+    self._last_dumped_blob = None
+
+  def start(self):
+    """Starts a thread that dumps value to the file."""
+    assert self._thread is None
+    self._dump() # initial dump
+    self._signal = Queue.Queue()
+    self._thread = threading.Thread(
+      target=self._run,

[M-A Ruel, 2016/06/03 20:00:49]

normally +4

[Vadim Sh., 2016/06/03 23:37:55]

Done.

+      args=(self._signal,),
+      name='FileRefresher %s' % self._path)
+    self._thread.daemon = True
+    self._thread.start()
+
+  def stop(self):
+    """Stops the dumping thread (if it is running)."""
+    if not self._thread:
+      return
+    self._signal.put(None)
+    self._thread.join(60) # don't wait forever
+    if self._thread.is_alive():
+      logging.error('FileRefresher thread failed to terminate in time')
+    self._signal = None
+    self._thread = None
+
+  def _dump(self):
+    try:
+      blob = json.dumps(
+          self._producer_callback(),
+          sort_keys=True,
+          indent=2,
+          separators=(',', ': '))
+    except Exception:
+      logging.exception('Unexpected exception in the callback')
+      return
+    if blob == self._last_dumped_blob:
+      return # 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 # 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
+      attempts -= 1
+      time.sleep(0.1)
+
+  def _run(self, signal):

[M-A Ruel, 2016/06/03 20:00:49]

why have you made it reusable, e.g. we can start()/stop() repeatedly. I don't
think this is needed and this could quite simplify the code.

[Vadim Sh., 2016/06/03 23:37:55]

I didn't intend it to be reusable, I just happened to write it that way... Made
it less reusable :-/ Not sure code is  much simpler.

+    while True:
+      try:
+        signal.get(timeout=self._interval_sec)
+        return # the stop signal received, quit the thread
+      except Queue.Empty:
+        self._dump()