[Cronet] Initial implementation of HttpURLConnection

components/cronet/android/java/src/org/chromium/net/urlconnection/MessageLoop.java

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.net.urlconnection;
+
+import java.util.concurrent.BlockingQueue;
+
+/**
+ * A package protected MessageLoop class for use in
+ * {@link CronetHttpURLConnection}
+ */
+final class MessageLoop {
+    private final BlockingQueue<Message> mQueue;
+
+    public MessageLoop(BlockingQueue<Message> queue) {
+        mQueue = queue;
+    }
+
+    /**
+     * Runs the message loop. Be sure to call {@link MessageLoop#quit()} to end
+     * the loop.
+     */
+    public void loop() {
+        while (true) {
+            try {
+                Message msg = mQueue.take(); // Blocks if the queue is empty.
+                if (msg.mTask != null) {
+                    msg.mTask.run();
+                } else {
+                    // Quits the message loop.
+                    break;
+                }
+            } catch (InterruptedException e) {
+                e.printStackTrace();
+            }
+        }
+    }
+
+    /**
+     * Quits the loop. This causes the {@link MessageLoop#loop()} to terminate
+     * after processing all currently enqueued messages.
+     */
+    public void quit() {
+        try {
+            mQueue.put(new Message(null));
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+    }
+
+    /**
+     * Message class that represents a task to run.
+     */
+    static class Message {
+        private final Runnable mTask;
+
+        /**
+         * Constructs a Message with a given task.
+         * @param task If null, it is a quit signal to the message loop.
+         */
+        public Message(Runnable task) {
+            mTask = task;
+        }
+    }
+}