[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;
+import java.util.concurrent.LinkedBlockingQueue;
+
+/**
+ * A package protected MessageLoop class for use in
+ * {@link CronetHttpURLConnection}.
+ */
+final class MessageLoop {
+    private final BlockingQueue<Runnable> mQueue;
+    // A reusable runnable to quit the message loop.
+    private final Runnable mQuitTask;
+    // Indicates whether this message loop is currently running.
+    private boolean mLoopRunning;
+
+    public MessageLoop() {
+        mQueue = new LinkedBlockingQueue<Runnable>();
+        mQuitTask = new Runnable() {
+            @Override
+            public void run() {
+                mLoopRunning = false;
+            }
+        };
+    }
+
+    /**
+     * Runs the message loop. Be sure to call {@link MessageLoop#postQuitTask()}
+     * to end the loop.
+     * @throws InterruptedException
+     */
+    public void loop() throws InterruptedException {
+        if (mLoopRunning) {
+            throw new IllegalStateException(
+                    "Cannot run loop when it is already running.");
+        }
+        mLoopRunning = true;
+        while (mLoopRunning) {
+            Runnable task = mQueue.take(); // Blocks if the queue is empty.
+            task.run();
+        }
+    }
+
+    /**
+     * Posts a reusable runnable, {@link #mQuitTask} to quit the loop. This
+     * causes the {@link #loop()} to terminate after processing all currently
+     * enqueued messages.
+     * @throws InterruptedException
+     */
+    public void postQuitTask() throws InterruptedException {
+        mQueue.put(mQuitTask);
+    }
+
+    /**
+     * Posts a task to the message loop.
+     * @throws InterruptedException
+     */
+    public void postTask(Runnable task) throws InterruptedException {
+        if (task == null) {
+            throw new IllegalArgumentException();
+        }
+        mQueue.put(task);
+    }
+}