Add UiBlocker for DashboardFragment

If DashboardFragment detects blocker controllers, it won't display
until:
1. All blocking controllers finish bg works.
2. Timeout

This CL adds UiBlockerController to control this behavior and
BlockingSlicePreferenceController as an example.

Bug: 120803703
Test: atest SettingsUnitTests
Change-Id: I66fc194776d46ee49b3ec7685f3167834e673ba2

src/com/android/settings/dashboard/UiBlockerController.java

@@ -0,0 +1,101 @@
+/*
+ * Copyright (C) 2019 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.settings.dashboard;
+
+import android.util.Log;
+
+import androidx.annotation.NonNull;
+
+import com.android.settings.core.BasePreferenceController;
+import com.android.settingslib.utils.ThreadUtils;
+
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Control ui blocker data and check whether it is finished
+ *
+ * @see BasePreferenceController.UiBlocker
+ * @see BasePreferenceController.OnUiBlockListener
+ */
+public class UiBlockerController {
+    private static final String TAG = "UiBlockerController";
+    private static final int TIMEOUT_MILLIS = 500;
+
+    private CountDownLatch mCountDownLatch;
+    private boolean mBlockerFinished;
+    private Set<String> mKeys;
+    private long mTimeoutMillis;
+
+    public UiBlockerController(@NonNull List<String> keys) {
+        this(keys, TIMEOUT_MILLIS);
+    }
+
+    public UiBlockerController(@NonNull List<String> keys, long timeout) {
+        mCountDownLatch = new CountDownLatch(keys.size());
+        mBlockerFinished = keys.isEmpty();
+        mKeys = new HashSet<>(keys);
+        mTimeoutMillis = timeout;
+    }
+
+    /**
+     * Start background thread, it will invoke {@code finishRunnable} if any condition is met
+     *
+     * 1. Waiting time exceeds {@link #mTimeoutMillis}
+     * 2. All background work that associated with {@link #mCountDownLatch} is finished
+     */
+    public boolean start(Runnable finishRunnable) {
+        if (mKeys.isEmpty()) {
+            // Don't need to run finishRunnable because it doesn't start
+            return false;
+        }
+        ThreadUtils.postOnBackgroundThread(() -> {
+            try {
+                mCountDownLatch.await(mTimeoutMillis, TimeUnit.MILLISECONDS);
+            } catch (InterruptedException e) {
+                Log.w(TAG, "interrupted");
+            }
+            mBlockerFinished = true;
+            ThreadUtils.postOnMainThread(finishRunnable);
+        });
+
+        return true;
+    }
+
+    /**
+     * Return {@code true} if all work finished
+     */
+    public boolean isBlockerFinished() {
+        return mBlockerFinished;
+    }
+
+    /**
+     * Count down latch by {@code key}. It only count down 1 time if same key count down multiple
+     * times.
+     */
+    public boolean countDown(String key) {
+        if (mKeys.remove(key)) {
+            mCountDownLatch.countDown();
+            return true;
+        }
+
+        return false;
+    }
+}