Add support for multiple asynchronous browser startups.

content/public/android/java/src/org/chromium/content/browser/BrowserStartupController.java

+// Copyright 2013 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.content.browser;
+
+import android.content.Context;
+import android.os.Handler;
+import android.util.Log;
+
+import com.google.common.annotations.VisibleForTesting;
+
+import org.chromium.base.CalledByNative;
+import org.chromium.base.JNINamespace;
+import org.chromium.base.ThreadUtils;
+import org.chromium.content.common.ProcessInitException;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * This class controls how C++ browser main loop is run and ensures it happens only once.

[bulach, 2013/08/15 15:09:12]

s/is run/is started/

[nyquist, 2013/08/16 02:01:01]

Done.

+ *
+ * It supports kicking of the startup sequence in an asynchronous way. Startup can be called as many
+ * times as needed, but the browser process will still only be initialized once. All requests to

[bulach, 2013/08/15 15:09:12]

times as needed (for instance, multiple activities for the same application)

[nyquist, 2013/08/16 02:01:01]

Done.

+ * start the browser will always get their callback executed; if the browser process has already
+ * been started, the callback is called immediately, else it is called when initialization is
+ * complete.
+ *
+ * All communication with this class must happen on the main thread.
+ *
+ * This is a singleton, and stores a reference to the application context.
+ */
+@JNINamespace("content")
+public class BrowserStartupController {
+    public interface StartupCallback {
+        void run(int startupResult);

[bulach, 2013/08/15 15:09:12]

nit: maybe "onStartupComplete" ?

[nyquist, 2013/08/16 02:01:01]

Done. Split into two methods: onSuccess and onFailure.

+    }
+
+    private static final String TAG = "BrowserStartupController";
+
+    private static final Object LOCK = new Object();
+
+    private static BrowserStartupController sInstance;
+
+    private static boolean sBrowserMayStartAsynchronously = false;
+
+    @CalledByNative
+    private static boolean browserMayStartAsynchonously() {
+        return sBrowserMayStartAsynchronously;
+    }
+
+    @CalledByNative
+    private static void browserStartupComplete(int result) {
+        BrowserStartupController instance = null;
+        synchronized (LOCK) {
+            if (sInstance != null) {
+                instance = sInstance;
+            }
+        }
+        if (instance != null) {
+            instance.executeEnqueuedCallbacks(result);
+        }
+    }
+
+    // A list of callbacks that should be called when the async startup of the browser process is
+    // complete.
+    private final List<StartupCallback> mAsyncStartupCallbacks;
+
+    private final Context mContext;

[bulach, 2013/08/15 15:09:12]

nit: I heard rumors that this can cause leaks, specially from a long-lived
singleton like this object.. maybe make it a regular member and assign to null
at initializeAndroidBrowserProcess, since it won't be ever be needed again?

[nyquist, 2013/08/16 02:01:01]

Done.

+
+    // Whether the async startup of the browser process has started.
+    private boolean mHasStartedInitializingBrowserProcess;
+
+    // Whether the async startup of the browser process is complete.
+    private boolean mAsyncStartupDone;
+
+    BrowserStartupController(Context context) {
+        mContext = context;
+        mAsyncStartupCallbacks = new ArrayList<StartupCallback>();
+    }
+
+    public static BrowserStartupController get(Context context) {
+        synchronized (LOCK) {
+            if (sInstance == null) {
+                sInstance = new BrowserStartupController(context.getApplicationContext());
+            }
+            return sInstance;
+        }
+    }
+
+    /**
+     * Start the browser process asynchronously. This will set up a queue of UI thread tasks to
+     * initialize the browser process.
+     * <p/>
+     * Note that this can only be called on the UI thread.
+     *
+     * @param callback the callback to be called when browser startup is complete.
+     * @return Whether the queue of tasks was created successfully.

[bulach, 2013/08/15 15:09:12]

hmm... would it make sense to have this method "void" and then always
callback.run(error_code)?

[nyquist, 2013/08/16 02:01:01]

Done.

+     */
+    public boolean startBrowserProcessesAsync(final StartupCallback callback) {
+        assert ThreadUtils.runningOnUiThread() : "Tried to start the browser on the wrong thread.";
+        if (mAsyncStartupDone) {
+            // Browser process is already fully started, so we can immediately post the callback.
+            new Handler().post(new Runnable() {
+                @Override
+                public void run() {
+                    callback.run(-1);

[bulach, 2013/08/15 15:09:12]

nit: maybe define -1 as public static final int of the StartupCallback?
I think there's two possible values, "already_initialized" and
"failed_initialization", if we decide to go with the "void" above.

[nyquist, 2013/08/16 02:01:01]

Done.

+                }
+            });
+            return true;
+        }
+
+        // Browser process has not been fully started yet, so we defer executing the callback.
+        mAsyncStartupCallbacks.add(callback);
+
+        if (mHasStartedInitializingBrowserProcess) {
+            // We only want to try to initialize the browser process once, so we just return here.
+            return true;
+        } else {
+            // This is the first time we have been asked to start the browser process. We set the
+            // flag that indicates that we have kicked off starting the browser process.
+            mHasStartedInitializingBrowserProcess = true;
+
+            enableAsynchronousStartup();
+
+            // We can now try to initialize the Android browser process.
+            return initializeAndroidBrowserProcess();
+        }
+    }
+
+    @VisibleForTesting
+    void executeEnqueuedCallbacks(int startupResult) {
+        assert ThreadUtils.runningOnUiThread() : "Callback from browser startup from wrong thread.";
+        mAsyncStartupDone = true;
+        for (StartupCallback asyncStartupCallback : mAsyncStartupCallbacks) {
+            asyncStartupCallback.run(startupResult);
+        }
+        // We don't want to hold on to any objects after we do not need them anymore.
+        mAsyncStartupCallbacks.clear();
+    }
+
+    /**
+     * Ensure that the browser process will be asynchronously started up. This also ensures that we
+     * get a call to {@link #browserStartupComplete} when the browser startup is complete.
+     */
+    @VisibleForTesting
+    void enableAsynchronousStartup() {
+        sBrowserMayStartAsynchronously = true;

[bulach, 2013/08/15 15:09:12]

need to make find_bugs happy.

[nyquist, 2013/08/16 02:01:01]

Done.

+    }
+
+    @VisibleForTesting
+    boolean initializeAndroidBrowserProcess() {
+        try {
+            AndroidBrowserProcess.init(mContext, AndroidBrowserProcess.MAX_RENDERERS_LIMIT);

[bulach, 2013/08/15 15:09:12]

nit: 
Context context = mContext;
mContext = null;

[nyquist, 2013/08/16 02:01:01]

Done.

+        } catch (ProcessInitException e) {
+            Log.e(TAG, "Unable to start browser process.", e);
+            return false;
+        }
+        return true;
+    }
+}