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August 2010
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2010-08-26 »

The strange case of virtual machines on telephones

    "Look, theory says that a JIT can run as fast as, or maybe faster than, a statically compiled language. It might be slow right now, but it'll be much better when we get a real/better JIT. Plus, the new version is already a lot faster, and I'm looking forward to the next version, which they promise will have huge speed improvements."

    -- Every Java user since 1996

If you've been saying the above about your Android phone (or Blackberry), then you, too, have become part of the decade-and-a-half-long train wreck of computer science that is Java.

I'm often mystified at the rejection of reality displayed by the proponents of Java-like virtual machines. It seems a simple statement of fact: even after 14 years, Java is still much slower than native code, and you can see it clearly just by looking at any app for 10 seconds. And yet the excuses above keep coming. 14 years.

But then I think, I know how this delusion works. I've been guilty of it myself. At my first company, I pushed to have all our data interchange sent through an API that I designed - UniConf - which was unfortunately slower in almost all cases than not using it. The idea was that if only all our code could be 100% pure UniConf then we'd suddenly be able to realize tons of wonderful advantages.

But despite herculean efforts, the advantages never materialized. What materialized was a lot of slowness, a lot of excessive memory usage, and a lot of weird bugs that forced us to backtrack through seven layers of overly-generalized code to diagnose.

Luckily for me, lack of resources prevented my own madness from spreading too far. I'm much better now.1

But what would it be like if the madness had been successful? What if I had been responsible for a system that spread to millions of users worldwide, which in nearly every case made things visibly and obviously worse? What would that do to my psyche? I think it would be unbearable.

Which brings us to Java-like VMs on cell phones. I have a lot of sympathy here, because:

Java used to be a good idea. Really.

Java on cell phones has not always been obviously a bad idea. To see why, you have to understand a bit about how these systems evolved.

First of all, we have little visibility into the Java's original reason for being. We know what people said, but we don't know if they said that for marketing or retroactive justification. What we do know is that the original sales push behind Java was applets for your web browser. Rich, client-side web applications.

Client-side web applications have exactly one super difficult critical requirement: security. You're downloading random apps from the Internet automatically and you want to run them automatically, and some of these apps will definitely be written by evil people and try to screw you, so you need a defense mechanism. Moreover, most people doing this will be doing it on Windows, which at the time meant Windows 95, which had no actual security whatsoever. Any native code could do anything it wanted. This situation persisted, mostly, up to and including Windows XP. (NT-based kernels have security, but the average person just ran everything as an administrator, negating literally all of it.)

So the typical user's operating system provided no strict memory protection or any other security features. This is where Java made perfect sense: if you can provably enforce security at the application layer, you can make a virtual machine that actually includes these missing security features, thus making it safe to run random applications on the Internet, and propelling us into the Internet Age. Sweet.

Java happened to fail at that, mostly due to slowness and crappiness and licensing, but the idea was sound, and it was a valiant and worthwhile effort that deserves our respect even if it didn't work out. Flash and Javascript won out in the end because they were somewhat better in some ways, but they both use VMs (whether interpreted or JITed), and rightly so.2

Unfortunately, nowadays the vast majority of Java apps never use any of Java's security features; they run as apps with full user rights, either on the client or on the server. So that advantage of the VM is gone... and the Java VM has no other advantages.3 But people, having been fooled once, kept going on the path they were already on.

Now ironically, the real problem was not natively compiled languages, but Windows (or to be generous to Microsoft, "the operating systems at the time"). Anybody who has studied computer science knows that modern processors capable of virtual memory were designed around the idea of keeping untrusted apps under control. Once upon a time, people used to actually share time on Unix machines. Lots of people on a few machines. And they were largely prevented from stomping on each other. The exceptions were security holes - fixable mistakes - and VMs have those too.

It is really not that hard to lock an application into a protected environment when your processor includes security features. Just google for chroot, BSD jail, AppArmor, SELinux. Yes, some of them are a little complex, but security is complex; nobody ever claimed Java's security architecture was simple.

Of course, if I had said that five years ago, you might not have believed me; you might have said those systems weren't secure enough, and that Java was somehow more secure in ways you couldn't quantify, but that application-level VM security is just somehow better somehow, I mean look at the virus situation on Windows. And I wouldn't be able to argue with you, because that's not even a logical argument, but it sounds vaguely convincing. And so the world went.

Then Apple came along and made the iPhone and its App Store and all the apps are native and the thing is still secure and apps can't stomp all over the system. Again, modulo security holes - fixable mistakes - which VMs don't eliminate. Here everybody was, going along with the above illogical argument in favour of VM security because they couldn't argue with it, and Apple just ignored them and showed it was all wrong. You can make native code secure. Of course you can. People did it in the 1980's. What on earth were we thinking?

But I'm getting ahead of the story a bit. Now I've told you why Android's use of a Java-like VM was demonstrably wrong (Apple demonstrated it) from the beginning, but first I wanted to tell you why Blackberries use Java, and lots of old cell phones used Java, and that wasn't obviously wrong.

The reason, of course, is that when Java was first applied to mobile phones, mobile phones didn't have processors capable of protected memory. Those processors were really low powered; security was impossible. Before Java, you could write custom native apps for a Blackberry... as long as you gave your source code to RIM to have them review it. Because native code could do anything, and there was physically no way to stop it once it got onto the device. Other phone manufacturers didn't even bother.

At the time, the first inexpensive embedded processors supporting protected memory were years in the future. If you could have a way to safely load third-party apps onto your phone... well, wow. You'd rule the world. You wouldn't just have a phone, you'd have a platform. This was not silliness, not at all. A Java VM was the first serious possibility of making a mobile phone into a serious, flexible, reconfigurable application platform.

It didn't work out very well, mostly because of Java's slowness and crappiness and licensing and (in the case of Java ME) horrendous lack of standardization. But GMail and Google Maps worked on my Blackberry, and millions of enterprise Blackberries are deployed running thousands of custom legacy enterprise apps you've never heard of that will make transitioning big established companies from Blackberry to iPhone virtually impossible for many years. In this case, pure thickheaded brute force did manage to win the day.

So okay, for the same reason that Java VMs started out as a good idea on Windows - namely, the platform itself lacked any security features - Java VMs made sense on phones. At first.

But embedded processors don't have those limitations anymore. They're serious processors now, with protected memory and everything. Most importantly, these processors were available and being used from the first day the first Google Phone was released. You no longer need a VM for security... but that means the VM doesn't provide any advantage at all.3

The fact that an Android phone has tolerable performance is, again, a triumph of pure thickheaded brute force. If you throw enough geniuses at a difficult technical problem, you might eventually solve that problem, even if the problem was stupid, and in this case, they mostly did.

But every step of the way, they're going to have this giant anchor of UniConf Dalvik tied around their neck, and Apple won't, and Apple's native apps will always run faster. It's going to be frustrating.

Maybe the speed won't matter. Maybe computers will get so fast that you just won't care anymore.

Java users have been saying that, too, since 1996.

Footnotes

1 I hope

2 Writing native desktop or server applications (ie. ones without crazy strict security requirements) using a Flash ("Adobe Air") or Javascript VM is kind of dumb for the same reasons set out in this article. There is one redeeming attribute of those systems, however: they already exist. If you have to have a VM for security on the web, then it makes sense to copy the runtime verbatim to the desktop/server, just because it's easier. Removing the VM would be possible and very nice, but it's just an optimization. Keeping the VM is easier, not harder, and thus is justifiable. (This doesn't really apply to Java since it never actually got popular for web apps.)

3 To pre-emptively refute a few common claims: "Write once run anywhere" doesn't actually work because the compiler was never the main problem; differences in OS semantics is the main problem, and you have to solve those equally for your apps in any language, even Java. Garbage collection can be and is frequently done in natively compiled languages. Introspection can be done in natively compiled languages. Digital signing of shared libraries can be implemented by any native shared library loader. Cross-language integration can be and is done all the time in native languages; in fact, VMs make this much harder, not easier, since now you have to rewrite all your languages. Sensible threading primitives (which some would say Java lacks anyway) can be implemented in any sensible language, natively compiled or not. Profile-driven optimization can be done in compiled languages. Support for multiple hardware architectures is just a recompile away - just ask any Mac developer. Provable memory protection (including prevention of all attempted null pointer dereferences) is doable and has been done in statically compiled languages. And before anyone asks, no, C/C++ does not do all these things; you need a good language. My point is that the good language needn't run in a VM; the VM is a red herring, a distraction.

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