Create ConnectivityThread

Create a common singleton thread to be shared among all
connectivity tasks.  Instead of launching separate threads to
handle downstream messages from the various service instances used
in connectivity, these managers can choose to share this instance.

Bug: 27695292

Change-Id: Idd1e37a3e793c5485091509c3d7351e4d29288f0
diff --git a/core/java/android/net/ConnectivityThread.java b/core/java/android/net/ConnectivityThread.java
new file mode 100644
index 0000000..55c3402
--- /dev/null
+++ b/core/java/android/net/ConnectivityThread.java
@@ -0,0 +1,51 @@
+/*
+ * Copyright (C) 2016 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 android.net;
+
+import android.os.HandlerThread;
+import android.os.Looper;
+
+/**
+ * Shared singleton connectivity thread for the system.  This is a thread for
+ * connectivity operations such as AsyncChannel connections to system services.
+ * Various connectivity manager objects can use this singleton as a common
+ * resource for their handlers instead of creating separate threads of their own.
+ * @hide
+ */
+public final class ConnectivityThread extends HandlerThread {
+    private static ConnectivityThread sInstance;
+
+    private ConnectivityThread() {
+        super("ConnectivityThread");
+    }
+
+    private static synchronized ConnectivityThread getInstance() {
+        if (sInstance == null) {
+            sInstance = new ConnectivityThread();
+            sInstance.start();
+        }
+        return sInstance;
+    }
+
+    public static ConnectivityThread get() {
+        return getInstance();
+    }
+
+    public static Looper getInstanceLooper() {
+        return getInstance().getLooper();
+    }
+}