Optimize latency when unlocking phone

Latency when unlocking the phone regressed a bit for two reasons:
- For lockscreen -> app we now have to create a full starting
window containing the snapshot, while previously this was just
showing a surface.
- For lockscreen -> home, we can't use the saved surface anymore
because currently we don't support snapshotting translucent
activities. However, in the long term, we want home screen to be
more involved into transitions anyways, so we'll have to wait for
the first frame draw anyways.

However, crystal ball trainee developer Jorim added some
artificial latency in this transition 3 years ago, because he knew
that it is going to be an issue at some point so we have some
headroom to improve! Genius! On a more serious note, it was because
he didn't understand how to read systraces with binders involved (to
be fair, there was also no binder tracing).

Now, we can completely fix the introduces latencies above by
removing this latency of 100ms, and we are 30-70ms better than
before! However, this requires a lot of discipline in SystemUI.
Currently, the callback to dismiss Keyguard takes around 30ms. By
moving all non-essential binder calls of the main thread or to the
next frame, we bring this down to 5ms, such that window animation
and Keyguard animation starts about at the same time.

Test: Take systrace, unlock phone...profit!

Change-Id: I3ea672bc2eca47221bc6c9f3d7c56b6899df207d
Fixes: 38294347

1 files changed, 34 insertions, 0 deletions

diff --git a/packages/SystemUI/src/com/android/systemui/UiOffloadThread.java b/packages/SystemUI/src/com/android/systemui/UiOffloadThread.java
new file mode 100644
index 000000000000..82fd9b304195
--- /dev/null
+++ b/packages/SystemUI/src/com/android/systemui/UiOffloadThread.java
@@ -0,0 +1,34 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License
+ */
+
+package com.android.systemui;
+
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+
+/**
+ * Thread that offloads work from the UI thread but that is still perceptible to the user, so the
+ * priority is the same as the main thread.
+ */
+public class UiOffloadThread {
+
+    private final ExecutorService mExecutorService = Executors.newSingleThreadExecutor();
+
+    public Future<?> submit(Runnable runnable) {
+        return mExecutorService.submit(runnable);
+    }
+}