Do I need to code things differently for ART vs Dalvik?

Question

I've been seeing reports (rumours) that soon Android will be switching from Dalvik to ART as it's default runtime. I have no real idea what that means, my guess the runtime is (kind of?) like the operation system.

My app doesn't do anything particularly special/unique in the sense of mostly it makes HTTP requests for data, and uses LocationListeners a few times.

On some articles I've read about the rumored change, I've seen some people saying things along the lines of "I like ART, I'd use it right now if X app supported it". (One app I remember being mentioned is Xposed)

I've switched my phone to ART, and my app seems to work fine, so I'm guessing the answer to the title question is no, but I'm curious as to how the Xposed app isn't compatible. What have they done (or not done) to make their app not work in ART?

Answer 1

ART is a different runtime for Android applications. All android apps run inside of a virtual machine, much like java code runs in the Java VM.

Classically, when you compiled an Android app, it would compile to Dalvik byte code, designed to run in the Dalvik runtime (virtual machine).

In Android Kitkat though, Google introduced a new experimental runtime called Android Runtime, or ART. This is a different virtual machine, a re-implementaton of the runtime for Android applications to help fix some of the fundamental flaws in the original design.

ART offers several advantages over Dalvik:

• Ahead-of-time (AOT) compilation
• Improved garbage collection
• Development and debugging improvements
  • Support for sampling profiler
  • Support for more debugging features
  • Improved diagnostic detail in exceptions and crash reports

It should also help with things like the DEX limit.

As to your question, you do not need to do anything as a developer. Google has said plainly that "Dalvik must remain the default runtime or you risk breaking your Android implementations and third-party applications".

Google has announced at Google I/O 2014 that in the Android "L" release and beyond, that ART will replace Dalvik.

Answer 2

ART has now replaced Dalvik on the Nexus devices, and my six existing apps, available in the Google Store, all now fail to run. I see multiple lists of questions about ART causing app failures. I suspect the "new and improved" memory managment garbage-collection is the root cause of much of this. My Samsung devices did not have an option to select ART instead of Dalvik, so I am only now getting user reports of the failures under Android 5.x. It is reported that the implementation of the native interface is significantly less forgiving, and requires different and more explicitly defined global pointers, where previously local pointers would operate correctly. This means anyone using native code, and the JNI (native interface), may have to re-code their app, or target a different platform with a more stable system architecture.