[Android] Mark posted UI thread tasks as asynchronous

base/android/java/src/org/chromium/base/SystemMessageHandler.java

Index: base/android/java/src/org/chromium/base/SystemMessageHandler.java
diff --git a/base/android/java/src/org/chromium/base/SystemMessageHandler.java b/base/android/java/src/org/chromium/base/SystemMessageHandler.java
index e1fbb0f4bed9538212313fdb374e81f0ac37f414..5f0b3d35dd22b9a941b286d169a53f9dcd6be884 100644
--- a/base/android/java/src/org/chromium/base/SystemMessageHandler.java
+++ b/base/android/java/src/org/chromium/base/SystemMessageHandler.java
@@ -6,18 +6,43 @@ package org.chromium.base;
 
 import android.os.Handler;
 import android.os.Message;
+import android.util.Log;
+
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
 
 class SystemMessageHandler extends Handler {
 
+    private static final String TAG = "SystemMessageHandler";
+
     private static final int SCHEDULED_WORK = 1;
     private static final int DELAYED_SCHEDULED_WORK = 2;
 
+    // Reflected API for marking a message as asynchronous. This is a workaround
+    // to provide *fair* Chromium task dispatch when served by the Android UI
+    // thread's Looper, avoiding stalls when the Looper has a sync barrier.
+    // Note: Use of this API is experimental and demonstrative, and is likely
+    // to be removed in the near future.
+    private Method mMessageMethodSetAsynchonous;
+
     // Native class pointer set by the constructor of the SharedClient native class.
     private long mMessagePumpDelegateNative = 0;
     private long mDelayedScheduledTimeTicks = 0;
 
     private SystemMessageHandler(long messagePumpDelegateNative) {
         mMessagePumpDelegateNative = messagePumpDelegateNative;
+
+        try {
+            Class<?> messageClass = Class.forName("android.os.Message");
+            mMessageMethodSetAsynchonous = messageClass.getMethod(
+                    "setAsynchronous", new Class[]{boolean.class});
+        } catch (ClassNotFoundException e) {
+            Log.e(TAG, "Failed to find android.os.Message class:" + e);
+        } catch (NoSuchMethodException e) {
+            Log.e(TAG, "Failed to load Message.setAsynchronous method:" + e);
+        } catch (RuntimeException e) {
+            Log.e(TAG, "Exception while loading Message.setAsynchronous method: " + e);
+        }
     }
 
     @Override
@@ -31,7 +56,7 @@ class SystemMessageHandler extends Handler {
     @SuppressWarnings("unused")
     @CalledByNative
     private void scheduleWork() {
-        sendEmptyMessage(SCHEDULED_WORK);
+        sendMessage(obtainAsyncMessage(SCHEDULED_WORK));
     }
 
     @SuppressWarnings("unused")
@@ -41,7 +66,7 @@ class SystemMessageHandler extends Handler {
             removeMessages(DELAYED_SCHEDULED_WORK);
         }
         mDelayedScheduledTimeTicks = delayedTimeTicks;
-        sendEmptyMessageDelayed(DELAYED_SCHEDULED_WORK, millis);
+        sendMessageDelayed(obtainAsyncMessage(DELAYED_SCHEDULED_WORK), millis);
     }
 
     @SuppressWarnings("unused")
@@ -51,6 +76,28 @@ class SystemMessageHandler extends Handler {
         removeMessages(DELAYED_SCHEDULED_WORK);
     }
 
+    private Message obtainAsyncMessage(int what) {
+        Message msg = Message.obtain();
+        msg.what = what;
+        if (mMessageMethodSetAsynchonous != null) {
+            // If invocation fails, assume this is indicative of future
+            // failures, and avoid log spam by nulling the reflected method.
+            try {
+                mMessageMethodSetAsynchonous.invoke(msg, true);
+            } catch (IllegalAccessException e) {
+                Log.e(TAG, "Illegal access to asynchronous message creation, disabling.");
+                mMessageMethodSetAsynchonous = null;
+            } catch (IllegalArgumentException e) {
+                Log.e(TAG, "Illegal argument for asynchronous message creation, disabling.");
+                mMessageMethodSetAsynchonous = null;
+            } catch (InvocationTargetException e) {
+                Log.e(TAG, "Invocation exception during asynchronous message creation, disabling.");
+                mMessageMethodSetAsynchonous = null;
+            }
+        }
+        return msg;
+    }
+
     @CalledByNative
     private static SystemMessageHandler create(long messagePumpDelegateNative) {
         return new SystemMessageHandler(messagePumpDelegateNative);