Add TareHandlerThread.

Create a separate thread for TARE so it doesn't get blocked by or block
other system components.

Bug: 158300259
Test: Android builds
Change-Id: Ib0989fb4c7332287ab2e6776d651298c50999e18

apex/jobscheduler/service/java/com/android/server/tare/TareHandlerThread.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright (C) 2021 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.server.tare;
+
+import android.os.HandlerThread;
+import android.os.Looper;
+import android.os.Trace;
+
+/**
+ * Singleton thread for all of TARE.
+ *
+ * @see com.android.internal.os.BackgroundThread
+ */
+final class TareHandlerThread extends HandlerThread {
+
+    private static TareHandlerThread sInstance;
+
+    private TareHandlerThread() {
+        super("tare");
+    }
+
+    private static void ensureThreadLocked() {
+        if (sInstance == null) {
+            sInstance = new TareHandlerThread();
+            sInstance.start();
+            final Looper looper = sInstance.getLooper();
+            looper.setTraceTag(Trace.TRACE_TAG_SYSTEM_SERVER);
+        }
+    }
+
+    static TareHandlerThread get() {
+        synchronized (TareHandlerThread.class) {
+            ensureThreadLocked();
+        }
+        return sInstance;
+    }
+}