Jvm.go: A JVM written in Go

https://github.com/zxh0/jvm.go

by tombenner • 11 years ago

284 123 11 years ago

github.com

slimsag• 11 years ago

First off -- this is really impressive! Is the author present here? I wonder:

- How is the performance?

- Is a GC implemented separately or is the Go one directly used (awesome!)?

- How do calls to native JNI things operate (through CGO)? Does it work?

pron3• 11 years ago

Not to take away from the author's effort, a basic JVM is not hard to implement. It's easier than writing a JavaScript or a Ruby interpreter, as the Java bytecode was designed for simple execution.

What is a lot of work is writing a high-performance JVM (with a good optimizing JIT and a good GC), getting the details right (especially the Java memory model), and supporting "advanced" features such as JNI and JVMTI.

xxs• 11 years ago

I was going to say: "the hard part of a JVM is the JIT, GC and the cooperation between. As it stands now I am not sure it's possible to write a good JVM on anything but C/asm level language."... But I see it's already done.

munificent3• 11 years ago

- How is the performance?

I'm guessing not great. Looks like a simple bytecode interpreter using interface virtual dispatch on the instructions (!).

- Is a GC implemented separately or is the Go one directly used (awesome!)?

As far as I can tell, it just uses the native Go GC, which is smart.

andrewchambers2• 11 years ago

Not smart, obvious.

millstone• 11 years ago

Java supports exotic reference types like weak references. These require close integration with the GC, and Go doesn't support them, so Go's GC can't be used to implement them.

jaytaylor3• 11 years ago

Will this open the door to utilizing Java libraries from within go apps?

Coming soon: scala.go (!)

mike_hearn10• 11 years ago

No - for that you'd need a Go implementation on the JVM.

Last time I checked there was a half finished student project that does this. But not a full implementation. That's a shame. I've encountered a Go shop that was really suffering from things as basic as "our best debugger is gdb which doesn't really work" and "how do we get a stack trace from our running program?".

The Go crowd like to talk about how Go programs are small and standalone, but obviously the HotSpot JVM is not just a big pile of NOPs. You can get very small implementations of Java too, but only by cutting lots of useful functionality.

I bet if a company produced a solid, compliant Go for the JVM, that'd be a license to print money. I feel like lots of startups are coding themselves into a corner by relying on the relatively new and simple Go runtime. If they could bring their code across to the JVM and get access to all the useful tools it has, that'd be worth some money.

bkeroack2• 11 years ago

Go on the JVM completely defeats one of the biggest Go selling points for me: compilation to native code.

Debuggers are definitely a weak spot, though, I agree. Luckily it's being worked on (https://github.com/derekparker/delve).

TheDong2• 11 years ago

Oh, yay, we can now get DOUBLE GC PAUSES!

I wish the README had more information about the reason this project exists. Is it just a fun toy jvm for learning? Is it meant to be eventually production-ready and performant?

Just knowing whether something is meant as a learning project or for production use vastly changes how people will approach it and I just can't tell with this one.

jaytaylor3• 11 years ago

glancing through the source code I don't see any reason there would be double gc pauses. This appears to be a full jvm, not exec.Command("java", ...).Run().

BinaryIdiot2• 11 years ago

The JVM handles the garbage collection for Java so if someone writes a JVM in a garbage collected language I would suspect two garbage collectors to be running (one for GO and one for the bytecode the JVM is running).

It would be an interesting concept to pass through Java objects for the GO garbage collector to deal with but that sounds incredibly difficult or impossible.

ricccardo• 11 years ago

I think what he means is that Go's built-in GC cannot be used to handle GC for the JVM. So the developer probably has to develop a GC for JVM data in Go. But since Go is a GCed language, the implementation of the JVM GC itself will be GCed at times. So you have two nested garbage collectors.

gus_massa• 11 years ago

tombenner posted a comment with a link to the author's blog: https://news.ycombinator.com/item?id=9203594

A relevant post by the author (English translation): http://translate.google.com/translate?hl=en&sl=zh-CN&u=http:... .

Relevant (autotranslated) snip from the blog:

> Go itself is garbage collected language, so there is no separate jvm.go achieve garbage collection mechanism.

TheDong2• 11 years ago

Awesome, I'm happy to be wrong there.

I saw the following code and noticed the commented out "gc" function and assumed it meant it was just "not yet implemented but will be" vs "unneeded". I wish the code was actually documented somewhat.

https://github.com/zxh0/jvm.go/blob/dd74e6227e9d78ad8ec191ec...

stcredzero• 11 years ago

Oh, yay, we can now get DOUBLE GC PAUSES!

I've also been in a position where I've exclaimed something "clever," only to find out later that it actually revealed a point of ignorance.

Dewie2• 11 years ago

Virtual machine implemented in GCd language -> Get ready, On your marks, FUD.

slowmovintarget2• 11 years ago

Now put a Lisp on there, quick! Clogure?

fnordsensei2• 11 years ago

Shouldn't Clojure work out of the box if it implements the same API as the JVM?

slowmovintarget2• 11 years ago

If it's JLS compliant, absolutely.

tombenner• 11 years ago

A relevant post by the author (English translation): http://translate.google.com/translate?hl=en&sl=zh-CN&u=http:...

deitcher• 11 years ago

It is pretty impressive as a project, but I am not sure I get the point. JVM already exists, so we can run Java programs. Go exists so we can compile Go programs. What do I get from running a Java program in a Go-built JVM over a C-built JVM?

jaytaylor3• 11 years ago

Minor note: go is now self-hosted which means it is no longer wrapped in c.

Leon• 11 years ago

There aren't always great reasons behind great hacks.

We can appreciate them for the ideas they present, the interesting implementation of features, and the what-if's that can come from expanding the hack further.

i_s2• 11 years ago

Depending on how it is done, one benefit could be you'd be able to use java/clojure/scala to build command line tools, something few people do now because of the slow JVM startup time.

sitkack3• 11 years ago

The JVM isn't too slow for command line tools. What is too slow is the size of the executables and the amount of upfront work that secondary runtimes are doing. I can't say anything for Scala, but the startup time of Clojure has nothing to do with the JVM.

Pure Java Hello World launches in 90ms on my machine. Jython Hello World takes 1.3 seconds.

EDIT: to address all the comments.

I am saying the JVM isn't _too_ slow for command line applications. Not ideal, but tolerable.

I just tested the startup time of a robovm'ed Hello World: 23ms FWIW. And the resulting executable isn't exactly light weight.

    $ otool -L Main 
    Main:
        /usr/lib/libSystem.B.dylib
        /usr/lib/libiconv.2.dylib
        /usr/lib/libsqlite3.dylib
        /System/Library/Frameworks/Foundation.framework/Versions/C/Foundation
        /usr/lib/libstdc++.6.dylib


     $ du -sch Main 
         11M	Main

steveklabnik2• 11 years ago

JVM already exists

Actually there is no single "the JVM," even today. Various JVMs exist, commercial and free, that have their individual strengths.

bratsche• 11 years ago

Sometimes we build things just for the experience, just to learn as we build.

danellis2• 11 years ago

I've noticed from HN headlines that there's an odd focus on what programming language something is written in. Often they'll take the form of "A <thing that is already common> written in <recently popular language>", rather than a real USP. It's especially odd from a community that places so much emphasis on the importance of a good pitch.

ovis• 11 years ago

a community that places so much emphasis on the importance of a good pitch

A subset do, for sure. But some of us are just playing around.

fnordsensei2• 11 years ago

I absolutely understand where you are coming from, but then again we are enthusiasts. It has some kind of relevance to us on the basis of being a novelty. Compare, "car engine runs on plant sap".

Iftheshoefits2• 11 years ago

Think of it in terms of a typical 13 year old boy acting out, e.g. by climbing real high in a tree or doing tricks on his bike, to impress friends/girls. That's all this shit is, except it is targeted to a slightly different audience who will go out of their way to deny it. Not saying that applies to this particular project, just to your comment more generally.

Sometimes it is done just to learn, but it seems a bit silly to do it in public as it were.

skybrian• 11 years ago

It's important for libraries. If you're writing in Go, a Java library doesn't help you much. Think of it as an easy way to qualify leads.

For apps, it matters less but you still have to think about how easy it is to modify. That's why we care about open source, right?

Dewie2• 11 years ago

It's especially odd from a community that places so much emphasis on the importance of a good pitch.

A good pitch? Why does that even matter? 97% of these projects are for fun/as a learning exercise. If someone is interested those things, then they can check it out. If they aren't, then I guess the author misses out on a few GitHub stars. shrug

jray319• 11 years ago

There have been many different VMs implemented on top of JavaScript VM, and it is to be able to run codes written in different languages on JavaScript VM without porting effort. It is useful since there are systems only running JavaScript programs, such as web browsers. I guess the purpose of this project may be justified similarly as Go started off from frustration with JavaScript and Go enthusiasts are dreaming that it would replace JavaScript (or get a spot in every browser) in the future.

binarycrusader• 11 years ago

This looks really neat, but there's no license or copyright notices as far as I can tell. Author, please add a license to your repository!

hobarrera2• 11 years ago

There's a " LICENSE.txt"[sic] file now. Looks like it's MIT licensed.

filereaper• 11 years ago

This is a very cool project, I just hope Oracle's lawyers don't descend on this...they have a knack for ruining everything.

GFK_of_xmaspast• 11 years ago

On what grounds.

lclarkmichalek• 11 years ago

Yeah, I mean, just look what they did to the openjdk

szabba• 11 years ago

Any specifics for the unoriented?

rdtsc• 11 years ago

Really cool. Thanks for sharing!

gnuvince• 11 years ago

Very cool project, I like the focus on readability (even if at the cost of performance): that makes it a good example to show to people who want to learn about the implementation of languages and VMs.

jamescun• 11 years ago

This is one way to get generics in Go.

btzll• 11 years ago

slow clap

anon4• 11 years ago

No reified generics though.

perrygeo• 11 years ago

While we're at it, wonder if it runs JGo? Go compiled to java bytecode running on a JVM built in Go.

https://code.google.com/p/jgo/

keyle2• 11 years ago

1600 commits by one dude? 700 commits in January? An average of 23 commits a day? 12,000 lines written and 7,000 removed just that month. An average of 640 commits per month.

I may be naive. Am I missing something or this guy is an incredible code machine?

neilellis4• 11 years ago

Nah, that's a perfectly reasonable pace to work at when you have:

* Predefined explicit requirements (a tight spec).

* No distractions.

* No colleagues (i.e. you're working on a non-blocking single thread of execution).

* Enthusiasm.

* An unhealthy enjoyment of coding.

I have worked at this pace and I'm sure many others have, but you need to have those pre-requisites (and they are RARE!).

Bare in mind that if you're the only developer those commits probably haven't been tested and you're not worrying about damaging other people's code.

Of course, you can't scale that model :-)

Which btw is a fantastic real world analogy of why multi-threading can suck horrifically in some cases and why that parallel execution isn't always a good thing.

NOTE: None of that takes a way from a totally awesome and fearless project to take on and complete (which I believe it is?).

afarrell• 11 years ago

Alternately, if you are going super-TDD on things and committing after every test, that pace is also reasonable under the conditions you list. I was at about that rate when I once tried to write a scheme interpreter in javascript in a weekend. I mostly succeeded, but ran out of time before getting done with some special forms.

keyle2• 11 years ago

I don't know about you, but I could maybe keep that pace 3 days. Maybe 5. But 2.5 months?

tinganho• 11 years ago

Just turn off twitter and Facebook and you can reach that kind of level.

hobarrera2• 11 years ago

And Hacker News, of course. Otherwise you'll be here every 5 minutes reading the comments and... DAMN!

marktangotango• 11 years ago

Implementing vm opcodes is not what you'd call demanding. Look at the jvm spec, a lot of opcodes are really very similar. Pop, pop, binary op, push.

neilellis4• 11 years ago

If I could upvote this a 1000 times I would.

We need more people doing crazy sh*t like this. Java is a fantastic runtime - and a great language. But it has a huge amount of baggage. I'd love to see experiments int the open source arena playing around with alternatives to the standard Oracle JVM.

I'd love to see Android like alternatives for the desktop that re-use java's syntax but have less baggage and are not tied to Sun's view of what Java should be (Oracle's view of the language is actually a lot better than Sun's thank god).

There are countless Java developers who would like to reuse their knowledge but in a different set up. E.g. desktop not server, lightweight not heavyweight, systems level (like go/python) etc.

I keep hoping that one of these JVMs will end up going in their own direction one day not trying to achieve official Java compatibility.

Anyway kudos to the author.

kolev6• 11 years ago

What is the "baggage" of Java? This is just a JVM and Java's JVM has no much more baggage than any other implementation. In order for this to be practical in terms of performance, reliability, and so on, years have to pass and meanwhile Oracle JDK and OpenJDK are not gonna stay still.

As a side note, I really wonder how an engineer can use ghetto talk like "crazy sh*t" and especially in this forum here.

girvo• 11 years ago

ghetto talk

Excuse me?

neilellis4• 11 years ago

Yo bitches, I am not an engineer - you may have noticed that this is Hacker News - not Engineering Weekly. I ain't never built any machinery - or designed no bridges - I'm just mo programming wit deez wild fingers.

Take it easy - until you know the language well enough to know when someone is using a complement like 'crazy sh*t' - I wouldn't rush to judge them. Context is everything - as the first two words of this comment attest. Context is everything :-)

threeseed• 11 years ago

You do realise that Oracle's JVM isn't the only one and there are many open source JVM alternatives. Quite a few of which are designed for lightweight systems:

http://en.wikipedia.org/wiki/List_of_Java_virtual_machines

And I have no idea what you mean by baggage. I am assuming you mean "features" like JNI, JMX etc ?

If that is the case then the modularisation of the JVM is something that has been underway for a number of years now. It is targeted for Java 9 release:

http://openjdk.java.net/projects/jigsaw/

And there is no difference in the way Oracle or Sun has managed the JVM. Changes are still made through the JSR/JEP process.

And finally again no idea what you mean by countess Java developers wanting to reuse their knowledge but in a different environment.

Android is already an option as is Swing but honestly does anyone care about desktop apps these days ?

bjourne2• 11 years ago

Baggage: http://stackoverflow.com/questions/313584/what-is-the-concep...

Yes there are many JVM:s but most of them aren't any good.

neilellis4• 11 years ago

I mean we carry stuff around from the days when we (the Java community) felt 'more is good' - you know the days of spit Java Blueprints.

And there is no difference in the way Oracle or Sun has managed the JVM

Yet coincidentally more positive changes have happened to the language in the last 3 years than the previous 10? I see a language that was dying on it's feet coming back to life - so hence my feelings about Oracle's stewardship (right or wrong!).

And finally again no idea what you mean by countess Java developers wanting to reuse their knowledge but in a different environment.

Almost every Java programmer I know and/or meet has their 'other language'. That they use to solve problems that Java has failed in. But a common frustration is the need to relearn a similar but subtly different syntax. Concrete examples are NodeJS (and hence Nashorn, Vert.x et al) for lightweight format neutral APIs. Android for mobile :-) so hat's a win. Go for systems (Python in the past). Objective-C et al Desktop.

For me there is no concrete reason why we can't have these in Java (language). But in doing so we need to be willing to throw away components that don't fit. I.e. existing APIs, existing philosophies. Java is much more than the language, however so when tackling problems that aren't large scale serverside applications we need to adapt if we are to reuse. This is an area that I very much am interested in seeing develop. My specific case in hand is Android - which reuses Java skills but has a lot less to do with normal Java programming.

Hope that clarifies a bit.

vinceyuan• 11 years ago

Baggage? Do you want to say 'garbage'?

sova• 11 years ago

+1 for "baggage collection" ;D

lnanek2• 11 years ago

Well, I'm fine with the link because it says it was just done for learning, but you'll never get anything practically useful out of this. The performance of the real JVM is decades ahead...

lorddoig• 11 years ago

This is cool, but now there's a risk that tomorrow will bring us JVM.js with a kickstarter, trendy logo, and a subtle but distinct whiff of moral superiority.

Edit: so I really am a cynic, I count at least two on the first page and neither are at all as wanky as my imagination likes to think.

andrewchambers2• 11 years ago

There are already a few jvm's written in Javascript.

xigency3• 11 years ago

That is the benefit of working on hard problems that are almost entirely technical. Especially if you are working alone, and usually not getting paid, it's easy to not get distracted by fad movements or popularization in simply writing software. But unfortunately, it usually ends up being a total waste of time.

Jvm.go: A JVM written in Go

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