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 FileRefresherThread(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.
+
+  The instance is not reusable (i.e. once stopped, cannot be started again).
+  """
+
+  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 = Queue.Queue()
+    self._last_dumped_blob = None
+
+  def start(self):

[M-A Ruel, 2016/06/06 21:18:36]

optional nit: I'm not sure start() is really needed, I'd just merge this
function into __init__(), same for FileReaderThread. But I don't mind.

[Vadim Sh., 2016/06/06 22:17:09]

Having explicit 'start' is better. It gives a chance to "register" the object in
all proper places before starting it.

+    """Starts a thread that dumps value to the file."""
+    assert self._thread is None
+    self._dump() # initial dump
+    self._thread = threading.Thread(
+        target=self._run, name='FileRefresherThread %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('FileRefresherThread failed to terminate in time')
+
+  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)

[M-A Ruel, 2016/06/06 21:18:36]

self._signal.get(timeout=0.05)

[Vadim Sh., 2016/06/06 22:17:09]

Done.

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