Wednesday, March 5, 2014

RyuJIT, Mono 3.2.7 and Java 9 (a possible future of stack virtual machines)

First of all I want to notice that a lot of development is in the area of managed runtimes so I want to give my personal take on this. This has nothing to do with the CR project, excluding that working on CR in my free time gives me more insight of the internals of these runtimes.

So what is known as of today:
- Microsoft works for a next-gen unified (no more 64 and 32 bit differences) .Net optimization framework that will be finished in an unspecified future version of .Net. From what we know, it has a much better Regex engine (that is it more than 10x faster than the previous ones) and an around 20% faster startup JIT times.
- Mono improves steadily (it has Loop Invariant Code Motion eventually) and it will rely more for Mono and LLVM integration for mobile phones.
- Java has a modular future with Java 9 (very similar with GAC in .Net, possible stack values and "compact" layout).

So what is the best runtime to invest today, knowing the next two years of proposed upgrades? As always the answer is: it depends. But I can try to split them by usage:
- want to implement a game: I would go with Mono. Mono has SIMD support, when for now .Net has no announced support. The workaround on the MS site is Mono. Even more, Mono supports LLVM as a backend and if it works ahead of time (at least for phone platforms). If you have a weird use-case, you can patch Mono and the Mono runtime.
- want to implement an application: if you want to use native standard controls use Mono. Mono has native controls on all platforms. You can import and develop it (fast) on Visual Studio tools and "migrate" it using for example XWT controls or Eto.Forms, in order not to redo the interface multiple times
- server side: if you will make all clients in Mono or .Net I would pick .Net. At least you can afford the price of Windows Server and/or pricier Visual Studio editions. If you are budget constrained I would pick Java all the way. Mono is a horrible choice. The reason is not how fast Mono runs (as Mono runs "just" two times slower) but because Java has a mature development platform for complex problems. Also, Mono tends to be a one, maybe two, language paradigm, but Java is polyglot: Ruby (and Mirah), Clojure, Kotlin or Scala are top-notch implementations with free IDEs. Even .Net is theoretically better, but the language support in the Java world today is far more vibrant
- fast response servers: today Java is the de-facto big-daddy of implementing fast response servers. Twitter moved from Ruby to Java. There are also more resources which are vendor neutral that document most of Java behaviors (DZone, InfoQ, Parleys, etc.).
- native application feeling (only for Windows): "native" is a word strangely defined by everyone, so I really dislike the term, but playing by its rules, if we define it as a Win32 looking application, the single solution is .Net with Windows Forms (or maybe Xwt). If we mean Windows with animations, the WPF is the single game in town. DevExpress controls are really standing out. Resharper (on Windows) can guarantee great code quality for your application too. OpenSource solutions do not provide something that matches WPF for now, but who knows? Maybe a future designer for XWT will appear for something like this.

So given this preamble, what I would want to see, per platform:
I. Java
- make a low-overhead PInvoke like solution. This makes platform native/Java applications to work slow, so people tend to write them in Java only and skip Java all-together with a simple API.  The pieces will likely be available at the Java 9 release, as they propose stack based types and compact representation. Even more, the packed objects will occupy less memory, another common criticism for Java.
- make tiered-compilation default (even on 64 bit machines) and Jigsaw: Java has profiles of running like Client (fast startup, weak optimizations) and Server (slow startup, strong optimizations). Tiered compilation starts programs in the client mode, and later switches to Server mode for methods that get more optimization. Even better, it would be that the Server compiled methods would run on a separate thread. This can improve the responsiveness of applications
In fact, it looks to me that .Net is a bit into "maintenance mode", it looks that .Net wants to be the previous VB: a convenience runtime. This is maybe because .Net conflicted somewhat with C++ development and they want to have the two development modes: "the native-fast" C++ and managed with 80% of C++ performance. RyuJit seems to me an effort to simplify code, and this is great don't get me wrong, but other features are missing and some users are missing them, for example a performance mode (there is Server and Desktop mode, but the differences are not in generated code, but in GC configuration and which assemblies are exposed for the application). As for me, the possibility of annotating functions to use SIMD or at least to support Mono.SIMD would be awesome. At last, it would be nice to support a form of full ahead-of-time compilation. I mean to make an executable that depends on .Net and doesn't do any JIT. This can allow some optimizations that can make some usages of .Net in the real world (mostly on games) where it is today mostly avoided.
For me Mono as runtime is the most advanced, even more advanced than Java, as it supports multiple compilation profiles, ahead of time, LLVM, intrinsics, many platforms (phones OSes, NaCl). Even it sounds maybe picky, Mono for me is missing the user-friendliness (even if it is miles ahead than what it was, let's say, 5 years ago). MonoDevelop (Xamarin Studio) + NRefactory (the framework that is used to give semantic understanding of your code) of code is really good for opensource world, yet still is a bit ignored. Most people are using Mono as a backup runtime, not as their primary platform to develop on. Code-completion is still a bit buggy as of today.

As for Mono and .Net parts to improve, I can tell the two items I found them quite important: escape analysis, purity and read-only analysis: some objects can be proved that they never "bleed" their references. This sounds like a not so important optimization, but it can reduce the overhead to the GC, and this is not a small deal: if let's say 10% of objects are not allocated on heap but on stack, is a speedup with no runtime to optimize for. Even more, there are guarantees of non synchronizing for these variables (which again is a great deal). I would love to have an interpreter integrated with adaptive compilation, like Java does: simple methods that are not run enough time to not be compiled at all. This can mean a lot more optimization (maybe compilation can happen on a separate thread) but also fast(er) startup time.

At last, (you can skip if you are not interested in CodeRefractor per-se), as much as I think that dynamic-compilation is the best way for managed runtimes, I think also that a full static compilation is great for some usages. When your application occupies let's say 10 MB of memory (I know is very little for many GB of RAM today) and you want a fast start time as you want to do some processing, you will not be so happy, if you will see because your application has a GC memory area that is an extra 5-8 MB and the runtime itself occupies another 5 MB that your application to use double memory that you expect. Using a solution like CodeRefactor you can reduce the memory requirements for your application (if it can compile your application), because no runtime is is running independently with your running application and no GC also. Memory is less of a requirement today and we are told for many years that memory doesn't matter, but if you want to get a faster application, you should care about memory compactness of your data.