[android] Create Battery Utils to seperate power functionality

build/android/pylib/device/device_utils.py

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Provides a variety of device interactions based on adb.
 
 Eventually, this will be based on adb_wrapper.
 """
 # pylint: disable=unused-argument
 
@@ skipping 1420 matching lines @@
 
     Parameters passed to this function are passed directly to
     |logcat_monitor.LogcatMonitor| and are documented there.
 
     Args:
       timeout: timeout in seconds
       retries: number of retries
     """
     return logcat_monitor.LogcatMonitor(self.adb, *args, **kwargs)
 
+  # TODO(rnephew): Remove when battery_utils is switched to.
   @decorators.WithTimeoutAndRetriesFromInstance()
   def GetBatteryInfo(self, timeout=None, retries=None):
     """Gets battery info for the device.
 
     Args:
       timeout: timeout in seconds
       retries: number of retries
     Returns:
       A dict containing various battery information as reported by dumpsys
       battery.
     """
     result = {}
     # Skip the first line, which is just a header.
     for line in self.RunShellCommand(
         ['dumpsys', 'battery'], check_return=True)[1:]:
       # 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
 
+  # TODO(rnephew): Remove when battery_utils is switched to.
   @decorators.WithTimeoutAndRetriesFromInstance()
   def GetCharging(self, timeout=None, retries=None):
     """Gets the charging state of the device.
 
     Args:
       timeout: timeout in seconds
       retries: number of retries
     Returns:
       True if the device is charging, false otherwise.
     """
     battery_info = self.GetBatteryInfo()
     for k in ('AC powered', 'USB powered', 'Wireless powered'):
       if (k in battery_info and
           battery_info[k].lower() in ('true', '1', 'yes')):
         return True
     return False
 
+  # TODO(rnephew): Remove when battery_utils is switched to.
   @decorators.WithTimeoutAndRetriesFromInstance()
   def SetCharging(self, enabled, timeout=None, retries=None):
     """Enables or disables charging on the device.
 
     Args:
       enabled: A boolean indicating whether charging should be enabled or
         disabled.
       timeout: timeout in seconds
       retries: number of retries
     """
@@ skipping 10 matching lines @@
       command = self._cache['charging_config']['enable_command']
     else:
       command = self._cache['charging_config']['disable_command']
 
     def set_and_verify_charging():
       self.RunShellCommand(command, check_return=True)
       return self.GetCharging() == enabled
 
     timeout_retry.WaitFor(set_and_verify_charging, wait_period=1)
 
-  # TODO(rnephew): Make private when all use cases can use the context manager.
+  # TODO(rnephew): Remove when battery_utils is switched to.
   @decorators.WithTimeoutAndRetriesFromInstance()
   def DisableBatteryUpdates(self, timeout=None, retries=None):
     """ Resets battery data and makes device appear like it is not
     charging so that it will collect power data since last charge.
 
     Args:
       timeout: timeout in seconds
       retries: number of retries
     """
     def battery_updates_disabled():
       return self.GetCharging() is False
 
     self.RunShellCommand(
         ['dumpsys', 'batterystats', '--reset'], check_return=True)
     battery_data = self.RunShellCommand(
         ['dumpsys', 'batterystats', '--charged', '--checkin'],
         check_return=True)
     ROW_TYPE_INDEX = 3
     PWI_POWER_INDEX = 5
     for line in battery_data:
       l = line.split(',')
       if (len(l) > PWI_POWER_INDEX and l[ROW_TYPE_INDEX] == 'pwi'
           and l[PWI_POWER_INDEX] != 0):
         raise device_errors.CommandFailedError(
             'Non-zero pmi value found after reset.')
     self.RunShellCommand(['dumpsys', 'battery', 'set', 'usb', '0'],
                          check_return=True)
     timeout_retry.WaitFor(battery_updates_disabled, wait_period=1)
 
-  # TODO(rnephew): Make private when all use cases can use the context manager.
+  # TODO(rnephew): Remove when battery_utils is switched to.
   @decorators.WithTimeoutAndRetriesFromInstance()
   def EnableBatteryUpdates(self, timeout=None, retries=None):
     """ Restarts device charging so that dumpsys no longer collects power data.
 
     Args:
       timeout: timeout in seconds
       retries: number of retries
     """
     def battery_updates_enabled():
       return self.GetCharging() is True
 
     self.RunShellCommand(['dumpsys', 'battery', 'set', 'usb', '1'],
                          check_return=True)
     self.RunShellCommand(['dumpsys', 'battery', 'reset'], check_return=True)
     timeout_retry.WaitFor(battery_updates_enabled, wait_period=1)
 
+  # TODO(rnephew): Remove when battery_utils is switched to.
   @contextlib.contextmanager
   def BatteryMeasurement(self, timeout=None, retries=None):
     """Context manager that enables battery data collection. It makes
     the device appear to stop charging so that dumpsys will start collecting
     power data since last charge. Once the with block is exited, charging is
     resumed and power data since last charge is no longer collected.
 
     Only for devices L and higher.
 
     Example usage:
@@ skipping 69 matching lines @@
     """
     if not devices:
       devices = adb_wrapper.AdbWrapper.GetDevices()
       if not devices:
         raise device_errors.NoDevicesError()
     devices = [d if isinstance(d, cls) else cls(d) for d in devices]
     if async:
       return parallelizer.Parallelizer(devices)
     else:
       return parallelizer.SyncParallelizer(devices)
+
+  # TODO(rnephew): Implement cache class.
+  def GetCacheEntry(self, key):

[perezju, 2015/03/30 11:05:23]

I'm not sure I like this idea. Why would a class expose its private cache to the
public? Seems like an invitation to mess with its internal state, and break
assumptions that methods using the cache may be making about it.

We may want a Cache class (if we really feel like we need some features not
already provided by a simple dictionary), but even then I also think that the
_cache object itself should be a private member.

If BatteryUtils needs a cache, it should use its own private one, either some
instance of a fancy Cache class or just a simple dictionary. This would also
lessen the worry of "others" overriding what we put in the cache. Thoughts?

(Also, BatteryUtils does not seem to be using this yet. So maybe material for
another CL?)

[jbudorick, 2015/03/30 13:35:03]

BatteryUtils doesn't know how to control the lifetime of cache variables;
DeviceUtils does. The cache functionality is the only reason
GetCharging/SetCharging are in DeviceUtils. They'd otherwise be implemented
separately (which is the driving reason behind this change, iirc).

That said, the current implementation is still problematic. If DeviceUtils is
providing the cache, the implementation needs to keep the client caches separate
from its own cache.

[rnephew (Wrong account), 2015/03/30 17:50:29]

It will use this when it stops passing the calls through to device_utils and
does everything in its own implementation.
Done.

+    """Cache getter."""
+    return self._cache.get(key)
+
+  def SetCacheEntry(self, key, value, override=False):
+    """Cache setter."""
+    if key not in self._cache:
+      self._cache[key] = value
+    elif override and value != self._cache[key]:
+      logging.warning('%s already in cache. Overriding %s with %s.', key,
+                      self._cache[key], value)
+      self._cache[key] = value
+    else:
+      logging.warning('%s already in cache. Not overriding %s with %s.', key,
+                      self._cache[key], value)