Hold a wake lock while dozing when display updates are pending.

When the display state is DOZE or DOZE_SUSPEND, assume this means
that the AP may go to sleep at any time so hold a wake lock for
a little while starting when traversals are scheduled to ensure
that the AP remains awake long enough to draw and post the frame
to the display hardware.

This patch is somewhat approximate but should be good enough for
most devices today.

Note that the implementation uses the window manager to ensure that
the window which wants to draw is actually visible before acquiring
the wake lock.  There is a cost to this test (a round-trip) which
should not be significant today since we do not expect apps to draw
more than one frame or two while dozing.  However, if we wanted to
support animations in general, we might want to optimize it or
eliminate the check altogether (since we can already account for
the app's use of the wake lock).

Another way to implement this functionality might be for the view
hierarchy to listen for the power manager to report that it has entered
a non-interactive power state before deciding to poke draw locks.
This would be somewhat more accurate than watching the display state.
Also, the draw lock timeout logic could be implemented more directly
instead of using an ordinary timed wake lock.

Bug: 18284212
Change-Id: I84b341c678303e8b7481bd1620e634fe82cc4350

1 files changed, 15 insertions, 0 deletions

diff --git a/core/java/android/os/PowerManager.java b/core/java/android/os/PowerManager.java
index d52dd30..e303f61 100644
--- a/core/java/android/os/PowerManager.java
+++ b/core/java/android/os/PowerManager.java
@@ -205,6 +205,20 @@ public final class PowerManager {
     public static final int DOZE_WAKE_LOCK = 0x00000040;
 
     /**
+     * Wake lock level: Keep the device awake enough to allow drawing to occur.
+     * <p>
+     * This is used by the window manager to allow applications to draw while the
+     * system is dozing.  It currently has no effect unless the power manager is in
+     * the dozing state.
+     * </p><p>
+     * Requires the {@link android.Manifest.permission#DEVICE_POWER} permission.
+     * </p>
+     *
+     * {@hide}
+     */
+    public static final int DRAW_WAKE_LOCK = 0x00000080;
+
+    /**
      * Mask for the wake lock level component of a combined wake lock level and flags integer.
      *
      * @hide
@@ -489,6 +503,7 @@ public final class PowerManager {
             case FULL_WAKE_LOCK:
             case PROXIMITY_SCREEN_OFF_WAKE_LOCK:
             case DOZE_WAKE_LOCK:
+            case DRAW_WAKE_LOCK:
                 break;
             default:
                 throw new IllegalArgumentException("Must specify a valid wake lock level.");