Adding an ExecutorFactory for the bindings.

mojo/bindings/java/src/org/chromium/mojo/bindings/ExecutorFactory.java

Index: mojo/bindings/java/src/org/chromium/mojo/bindings/ExecutorFactory.java
diff --git a/mojo/bindings/java/src/org/chromium/mojo/bindings/ExecutorFactory.java b/mojo/bindings/java/src/org/chromium/mojo/bindings/ExecutorFactory.java
new file mode 100644
index 0000000000000000000000000000000000000000..c153bc907d9b33902342b417cbbc9044688e1b0c
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+++ b/mojo/bindings/java/src/org/chromium/mojo/bindings/ExecutorFactory.java
@@ -0,0 +1,183 @@
+// 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.mojo.bindings;
+
+import org.chromium.mojo.system.AsyncWaiter;
+import org.chromium.mojo.system.AsyncWaiter.Callback;
+import org.chromium.mojo.system.Core;
+import org.chromium.mojo.system.MessagePipeHandle;
+import org.chromium.mojo.system.MessagePipeHandle.ReadMessageResult;
+import org.chromium.mojo.system.MojoException;
+import org.chromium.mojo.system.MojoResult;
+import org.chromium.mojo.system.Pair;
+
+import java.nio.ByteBuffer;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.Executor;
+
+/**
+ * A factory which provides per-thread executors, which enable execution on the thread from which
+ * they were obtained.
+ */
+class ExecutorFactory {
+
+    /**
+     * A null buffer which is used to send messages without any data on the PipedExecutor's
+     * signaling handles.
+     */
+    private static final ByteBuffer NOTIFY_BUFFER = null;
+
+    /**
+     * Implementation of the executor which uses a pair of {@link MessagePipeHandle} for signaling.
+     * The executor will wait asynchronously on one end of a {@link MessagePipeHandle} on the thread
+     * on which it was created. Other threads can call execute with a {@link Runnable}, and the
+     * executor will queue the {@link Runnable} and write a message on the other end of the handle.
+     * This will wake up the executor which is waiting on the handle, which will then dequeue the
+     * {@link Runnable} and execute it on the original thread.
+     */
+    private static class PipedExecutor implements Executor, Callback {
+
+        /**
+         * The handle which is written to. Access to this object must be protected with |mLock|.
+         */
+        private final MessagePipeHandle mWriteHandle;
+        /**
+         * The handle which is read from.
+         */
+        private final MessagePipeHandle mReadHandle;
+        /**
+         * The list of actions left to be run. Access to this object must be protected with |mLock|.
+         */
+        private final List<Runnable> mPendingActions;
+        /**
+         * Lock protecting access to |mWriteHandle| and |mPendingActions|.
+         */
+        private final Object mLock;
+        /**
+         * The {@link AsyncWaiter} to get notified of new message availability on |mReadHandle|.
+         */
+        private final AsyncWaiter mWaiter;
+
+        /**
+         * Constructor.
+         */
+        public PipedExecutor(Core core) {
+            mWaiter = core.getDefaultAsyncWaiter();
+            assert mWaiter != null;
+            mLock = new Object();
+            Pair<MessagePipeHandle, MessagePipeHandle> handles = core.createMessagePipe();
+            mReadHandle = handles.first;
+            mWriteHandle = handles.second;
+            mPendingActions = new ArrayList<Runnable>();
+            asyncWait();
+        }
+
+        /**
+         * Asynchronously wait for the next command to arrive. This should only be called on the
+         * executor thread.
+         */
+        private void asyncWait() {
+            mWaiter.asyncWait(mReadHandle, Core.WaitFlags.READABLE, Core.DEADLINE_INFINITE,
+                    this);
+        }
+
+        /**
+         * @see Callback#onResult(int)
+         */
+        @Override
+        public void onResult(int result) {
+            if (result == MojoResult.OK && readNotifyBufferMessage()) {
+                runNextAction();
+            } else {
+                close();
+            }
+        }
+
+        /**
+         * @see Callback#onError(MojoException)
+         */
+        @Override
+        public void onError(MojoException exception) {
+            close();
+        }
+
+        /**
+         * Close the handles. Should only be called on the executor thread.
+         */
+        private void close() {
+            synchronized (mLock) {
+                mWriteHandle.close();
+                mPendingActions.clear();
+            }
+            mReadHandle.close();
+        }
+
+        /**
+         * Read the next message on |mReadHandle|, and return |true| if successful, |false|
+         * otherwise.
+         */
+        private boolean readNotifyBufferMessage() {
+            try {
+                ReadMessageResult readMessageResult = mReadHandle.readMessage(NOTIFY_BUFFER, 0,
+                        MessagePipeHandle.ReadFlags.NONE);
+                if (readMessageResult.getMojoResult() == MojoResult.OK) {
+                    asyncWait();
+                    return true;
+                }
+            } catch (MojoException e) {
+                // Will be closed by the fall back at the end of this method.
+            }
+            return false;
+        }
+
+        /**
+         * Run the next action in the |mPendingActions| queue.
+         */
+        private void runNextAction() {
+            Runnable toRun = null;
+            synchronized (mWriteHandle) {
+                toRun = mPendingActions.remove(0);
+            }
+            toRun.run();
+        }
+
+        /**
+         * Execute the given |command| in the executor thread. This can be called on any thread.
+         *
+         * @see Executor#execute(Runnable)
+         */
+        @Override
+        public void execute(Runnable command) {
+            // Accessing the write handle must be protected by the lock, because it can be closed
+            // from the executor's thread.
+            synchronized (mLock) {
+                if (!mWriteHandle.isValid()) {
+                    throw new IllegalStateException(
+                            "Trying to execute an action on a closed executor.");
+                }
+                mPendingActions.add(command);
+                mWriteHandle.writeMessage(NOTIFY_BUFFER, null, MessagePipeHandle.WriteFlags.NONE);
+            }
+        }
+    }
+
+    /**
+     * Keep one executor per executor thread.
+     */
+    private static final ThreadLocal<Executor> EXECUTORS = new ThreadLocal<Executor>();
+
+    /**
+     * Returns an {@link Executor} that will run all of its actions in the current thread.
+     */
+    public static Executor getExecutorForCurrentThread(Core core) {
+        Executor executor = EXECUTORS.get();
+        if (executor == null) {
+            executor = new PipedExecutor(core);
+            EXECUTORS.set(executor);
+        }
+        return executor;
+    }
+}