Add new method to disable android device charging.

build/android/pylib/device/device_utils.py

Index: build/android/pylib/device/device_utils.py
diff --git a/build/android/pylib/device/device_utils.py b/build/android/pylib/device/device_utils.py
index b6fd7323bb9a3c71e566049719a963bba2ce9023..f17e8050696fc55306c8acd2a58bdf1e62a5e527 100644
--- a/build/android/pylib/device/device_utils.py
+++ b/build/android/pylib/device/device_utils.py
@@ -9,6 +9,7 @@ Eventually, this will be based on adb_wrapper.
 # pylint: disable=unused-argument
 
 import collections
+from contextlib import contextmanager

[jbudorick, 2015/03/12 13:25:57]

import contextlib, then use @contextlib.contextmanager

[rnephew (Wrong account), 2015/03/12 18:17:58]

Done.

 import itertools
 import logging
 import multiprocessing
@@ -69,6 +70,11 @@ _CONTROL_CHARGING_COMMANDS = [
   },
 ]
 
+_DEFAULT_CHARGING_COMMANDS = {
+    'witness_file': None,
+    'enable_command': 'dumpsys battery reset',
+    'disable_command': 'dumpsys battery set usb 0',
+}

[perezju, 2015/03/12 09:37:14]

I think this is no longer used, so you can remove it.

[rnephew (Wrong account), 2015/03/12 18:17:58]

Done.

 
 @decorators.WithExplicitTimeoutAndRetries(
     _DEFAULT_TIMEOUT, _DEFAULT_RETRIES)
@@ -1414,8 +1420,16 @@ class DeviceUtils(object):
     # Skip the first line, which is just a header.
     for line in self.RunShellCommand(
         ['dumpsys', 'battery'], check_return=True)[1:]:
-      k, v = line.split(': ', 1)
-      result[k.strip()] = v.strip()
+      # If usb charging has been disabled, an extra line of header exists.
+      if 'UPDATES STOPPED' in line:
+        logging.warning('Dumpsys battery not receiving updates. '
+                        'Run dumpsys battery reset if this is in error.')
+      elif ':' not in line:
+        logging.warning('Unknown line found in dumpsys battery.')
+        logging.warning(line)
+      else:
+        k, v = line.split(': ', 1)
+        result[k.strip()] = v.strip()
     return result
 
   @decorators.WithTimeoutAndRetriesFromInstance()
@@ -1466,6 +1480,31 @@ class DeviceUtils(object):
     timeout_retry.WaitFor(set_and_verify_charging, wait_period=1)
 
   @decorators.WithTimeoutAndRetriesFromInstance()

[perezju, 2015/03/12 09:37:14]

Not sure, but maybe we should remove the timeout retries from here, so that
timeouts and retries are handled by the individual RunShellCommand calls? John,
what do you think of this?

[jbudorick, 2015/03/12 13:25:57]

I think I've never seen this decorator applied to a context manager :)

I'm not actually sure how it would work, though if I had to guess, I'd say that
it probably winds up running both __enter__ and __exit__ on (separate)
TimeoutRetry threads.

I think the issue with just letting RunShellCommand handle timeouts and retries
is that the two WaitFor calls would no longer be inside TimeoutRetry threads,
and in this case, I think we want them there.

I think the context manager function should be dead simple -- something like:

  @contextlib.contextmanager
  def BatteryMeasurement(self):
    try:
      self._DisableBatteryUpdates()
      yield
    finally:
      self._EnableBatteryUpdates()

and then have both of the helper functions decorated with the timeout/retries
decorator.

[perezju, 2015/03/12 13:43:26]

+1

[rnephew (Wrong account), 2015/03/12 18:17:58]

Done.

+  @contextmanager
+  def BatteryMeasurement(self, timeout=None, retries=None):
+    """Enables or disables the power collection since last charge.

[perezju, 2015/03/12 09:37:14]

Update the doc string, and maybe add a small of example of how the context
manager would be used?

[rnephew (Wrong account), 2015/03/12 18:17:59]

Done.

+
+    Args:
+      timeout: timeout in seconds
+      retries: number of retries
+    """
+    def set_and_verify_battery_measurement():

[perezju, 2015/03/12 09:37:14]

I think it will be cleaner/more readable (also in the logs) if you define two
different functions "start_battery_measurement" and "finish_battery_measurement"
which you then wait-for in the try-finally bellow.

[jbudorick, 2015/03/12 13:25:57]

agreed

[rnephew (Wrong account), 2015/03/12 18:17:58]

Also added a separate reset_battery_data because of a possible yet unlikely race
condition where it resets the data and turns off power, but the device does not
yet report that power is turned off and the timeout occurs and on subsequent
retries it would check that power data is reset, but nothing would read 0 since
its collecting data.

+      self.RunShellCommand(command, check_return=True)

[jbudorick, 2015/03/12 13:25:57]

Note that what you've done here with command is sneaky at best.

[rnephew (Wrong account), 2015/03/12 18:17:58]

Acknowledged.

+      return self.GetCharging() is charging_state
+
+    try:
+      command = 'dumpsys batterystats --reset && dumpsys battery set usb 0'

[perezju, 2015/03/12 09:37:14]

split this into two calls to RunShellCommand, and pass the command as a list of
arguments (i.e. ['dumpsys', 'batterystats', '--reset'], etc.)

[rnephew (Wrong account), 2015/03/12 18:17:58]

Done.

+      charging_state = False
+      timeout_retry.WaitFor(set_and_verify_battery_measurement, wait_period=1)
+      yield
+
+    finally:
+      command = 'dumpsys battery reset'

[perezju, 2015/03/12 09:37:14]

ditto, use a list of arguments instead of a string. A string is fine if you
really need to use shell features, but otherwise a list of arguments is
preferred.

[rnephew (Wrong account), 2015/03/12 18:17:58]

Done.

+      charging_state = True
+      timeout_retry.WaitFor(set_and_verify_battery_measurement, wait_period=1)
+
+
+  @decorators.WithTimeoutAndRetriesFromInstance()
   def GetDevicePieWrapper(self, timeout=None, retries=None):
     """Gets the absolute path to the run_pie wrapper on the device.