History log of /frameworks/base/core/java/android/os/WorkSource.java
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9630704ed3b265f008a8f64ec60a33cf9dcd3345 28-Jul-2012 Jeff Brown <jeffbrown@google.com> Power manager rewrite.

The major goal of this rewrite is to make it easier to implement
power management policies correctly. According, the new
implementation primarily uses state-based rather than event-based
triggers for applying changes to the current power state.

For example, when an application requests that the proximity
sensor be used to manage the screen state (by way of a wake lock),
the power manager makes note of the fact that the set of
wake locks changed. Then it executes a common update function
that recalculates the entire state, first looking at wake locks,
then considering user activity, and eventually determining whether
the screen should be turned on or off. At this point it may
make a request to a component called the DisplayPowerController
to asynchronously update the display's powe state. Likewise,
DisplayPowerController makes note of the updated power request
and schedules its own update function to figure out what needs
to be changed.

The big benefit of this approach is that it's easy to mutate
multiple properties of the power state simultaneously then
apply their joint effects together all at once. Transitions
between states are detected and resolved by the update in
a consistent manner.

The new power manager service has is implemented as a set of
loosely coupled components. For the most part, information
only flows one way through these components (by issuing a
request to that component) although some components support
sending a message back to indicate when the work has been
completed. For example, the DisplayPowerController posts
a callback runnable asynchronously to tell the PowerManagerService
when the display is ready. An important feature of this
approach is that each component neatly encapsulates its
state and maintains its own invariants. Moreover, we do
not need to worry about deadlocks or awkward mutual exclusion
semantics because most of the requests are asynchronous.

The benefits of this design are especially apparent in
the implementation of the screen on / off and brightness
control animations which are able to take advantage of
framework features like properties, ObjectAnimator
and Choreographer.

The screen on / off animation is now the responsibility
of the power manager (instead of surface flinger). This change
makes it much easier to ensure that the animation is properly
coordinated with other power state changes and eliminates
the cause of race conditions in the older implementation.

The because of the userActivity() function has been changed
so that it never wakes the device from sleep. This change
removes ambiguity around forcing or disabling user activity
for various purposes. To wake the device, use wakeUp().
To put it to sleep, use goToSleep(). Simple.

The power manager service interface and API has been significantly
simplified and consolidated. Also fixed some inconsistencies
related to how the minimum and maximum screen brightness setting
was presented in brightness control widgets and enforced behind
the scenes.

At present the following features are implemented:

- Wake locks.
- User activity.
- Wake up / go to sleep.
- Power state broadcasts.
- Battery stats and event log notifications.
- Dreams.
- Proximity screen off.
- Animated screen on / off transitions.
- Auto-dimming.
- Auto-brightness control for the screen backlight with
different timeouts for ramping up versus ramping down.
- Auto-on when plugged or unplugged.
- Stay on when plugged.
- Device administration maximum user activity timeout.
- Application controlled brightness via window manager.

The following features are not yet implemented:

- Reduced user activity timeout for the key guard.
- Reduced user activity timeout for the phone application.
- Coordinating screen on barriers with the window manager.
- Preventing auto-rotation during power state changes.
- Auto-brightness adjustment setting (feature was disabled
in previous version of the power manager service pending
an improved UI design so leaving it out for now).
- Interpolated brightness control (a proposed new scheme
for more compactly specifying auto-brightness levels
in config.xml).
- Button / keyboard backlight control.
- Change window manager to associated WorkSource with
KEEP_SCREEN_ON_FLAG wake lock instead of talking
directly to the battery stats service.
- Optionally support animating screen brightness when
turning on/off instead of playing electron beam animation

Change-Id: I1d7a52e98f0449f76d70bf421f6a7f245957d1d7
94838913abf6363532cd32b9c795917d808228cc 27-Jul-2012 Jeff Brown <jeffbrown@google.com> Implement equals() and hashCode() like a good little object.

Change-Id: I06fc8f96586c72095ffa142d52fbd71af05cee97
83770289f8eca5aa4c62647a6c4d9a5bd4c80a45 14-Sep-2010 Dianne Hackborn <hackbod@google.com> Fix issue #2999795: Runtime restart on Crespo

Change-Id: I7138b031298a234f3f35aec4a003d25cf86a57ff
7e9f4eb2608148436cef36c9969bf8a599b39e72 11-Sep-2010 Dianne Hackborn <hackbod@google.com> Track client requests through location manager.

This fixes a problem where applications could ask the location
manager to do very heavy-weight things (like... say... update
location every minute), which would get accounted against the
system instead of the application because ultimately it is the
system making the heavy calls (wake locks, etc).

To solve this, we introduce a new class WorkSource representing
the source of some work. Wake locks and Wifi locks allow you
to set the source to use (but only if you are system code and thus
can get the permission to do so), which is what will be reported
to the battery stats until the actual caller.

For the initial implementation, the location manager keeps track
of all clients requesting periodic updates, and tells its providers
about them as a WorkSource param when setting their min update time.
The network location provider uses this to set the source on the
wake and wifi locks it acquires, when doing work because of the
update period.

This should also be used elsewhere, such as in the GPS provider,
but this is a good start.

Change-Id: I2b6ffafad9e90ecf15d7c502e2db675fd52ae3cf