[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 waiting for task has been interrupted. The loop cannot
+    // be safely started if it has been interrupted. Because this might cause
+    // the loop to terminate immediately if there is a quit task enqueued.
+    private boolean mWaitingInterrupted = 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 #mWaitingInterrupted}).
+     * @throws IOException
+     */
+    public void loop() throws IOException {
+        if (mWaitingInterrupted) {
+            throw new IllegalStateException(
+                    "Cannot run loop as the loop has been terminated.");
+        }
+        if (mLoopRunning) {
+            throw new IllegalStateException(
+                    "Cannot run loop when it is already running.");
+        }
+        mLoopRunning = true;
+        while (mLoopRunning) {
+            try {
+                Runnable task = mQueue.take(); // Blocks if the queue is empty.
+                task.run();
+            } catch (InterruptedException | RuntimeException e) {
+                mLoopRunning = false;
+                if (e instanceof InterruptedException) {
+                    mWaitingInterrupted = true;
+                    throw new IOException(e);
+                } else if (e instanceof RuntimeException) {

[xunjieli, 2014/12/03 19:03:30]

Not sure if this is what you have in mind..

[mmenke, 2014/12/03 20:05:39]

I'd like to prevent running the loop again here, too - I suspect other
implementations don't support trying to read against after an exception as well,
but I'm sufficiently paranoid that I'd like to throw an exception on future
calls to loop()  (Or could look into what other implementations do, and copy
them)

[xunjieli, 2014/12/03 20:46:52]

Done. I added a new test for this as well.

+                    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, 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 waiting for a task has been interrupted. Used in testing.
+     */
+    public boolean isWaitingInterrupted() {
+        return mWaitingInterrupted;
+    }
+}