[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.io.IOException;
+import java.util.concurrent.BlockingQueue;
+import java.util.concurrent.Executor;
+import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.RejectedExecutionException;
+
+/**
+ * A MessageLoop class for use in {@link CronetHttpURLConnection}.
+ */
+public final class MessageLoop implements Executor {
+    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 = false;
+
+    // Indicates whether an InterruptedException or a RuntimeException has
+    // occurred in loop(). If true, the loop cannot be safely started because
+    // this might cause the loop to terminate immediately if there is a quit
+    // task enqueued.
+    private boolean mLoopFailed = false;
+
+    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. If an interruptedException occurs, the loop cannot be
+     * started again (see {@link #mLoopFailed}).
+     * @throws IOException
+     */
+    public void loop() throws IOException {
+        if (mLoopFailed) {
+            throw new IllegalStateException(
+                    "Cannot run loop as an exception has occurred previously.");
+        }
+        if (mLoopRunning) {
+            throw new IllegalStateException(
+                    "Cannot run loop when it is already running.");
+        }
+        mLoopRunning = true;

[mef, 2014/12/04 20:37:56]

Can we get into the situation where loop() is called from different threads?

[xunjieli, 2014/12/04 20:55:53]

HttpURLConnection is not thread-safe, so clients should not share one connection
among threads. As long as they are using the connection in one thread, loop()
will always be called from the same thread.

+        while (mLoopRunning) {
+            try {
+                Runnable task = mQueue.take(); // Blocks if the queue is empty.
+                task.run();
+            } catch (InterruptedException | RuntimeException e) {
+                mLoopRunning = false;
+                mLoopFailed = true;
+                if (e instanceof InterruptedException) {
+                    throw new IOException(e);
+                } else if (e instanceof RuntimeException) {
+                    throw (RuntimeException) e;
+                }
+            }
+        }
+    }
+
+    /**
+     * Posts a reusable runnable, {@link #mQuitTask} to quit the loop. This
+     * causes the {@link #loop()} to stop after processing all currently
+     * enqueued messages.
+     */
+    public void postQuitTask() {
+        execute(mQuitTask);
+    }
+
+    /**
+     * Posts a task to the message loop.
+     */
+    @Override
+    public void execute(Runnable task) throws RejectedExecutionException {
+        if (task == null) {
+            throw new IllegalArgumentException();
+        }
+        try {
+            mQueue.put(task);
+        } catch (InterruptedException e) {
+            // In theory this exception won't happen, since we have an blocking
+            // queue with Integer.MAX_Value capacity, put() call will not block.
+            throw new RejectedExecutionException(e);
+        }
+    }
+
+    /**
+     * Returns whether the loop is currently running. Used in testing.
+     */
+    public boolean isRunning() {
+        return mLoopRunning;
+    }
+
+    /**
+     * Returns whether an exception occurred in {#loop()}. Used in testing.
+     */
+    public boolean hasLoopFailed() {
+        return mLoopFailed;
+    }
+}