Is it possible to code a device driver in Java?

Question

Introduction

I heard something about writing device drivers in Java (heard as in \"with my ears\", not from the internet) and was wondering... I always thought dev

Answer 1

For the motivation, please remember that there is plenty of fast languages which are better than C for programming; they might not be as fast as C, but they are safe languages: if you make a mistake you don't get undefined behavior. And "undefined behavior" includes executing arbitrary code supplied by some attacker which formats your HD. Many functional languages are usually compiled to native code.

Device drivers contain the most bugs in an OS kernel - I know that for Linux (Linus Torvalds and others keep saying so) and I heard that for Windows. While for a disk or Ethernet driver you need top-notch performance, and while in Linux drivers today are the bottleneck for 10G Ethernet or SSD disks, most drivers don't need that much speed - all computers wait at the same speed.

That's why there are various projects to allow writing drivers which run outside of the kernel, even if that causes a slowdown; when you can do that, you can use whatever language you want; you will just then need Java bindings for the hardware control library you use - if you were writing the driver in C, you would still have a library with C bindings.

For drivers in kernel mode proper, there are two problems that I've not yet seen mentioned:

• Garbage Collection, and that's a tough requirement. You need to write an in-kernel Garbage Collector; some GC algorithms rely on Virtual Memory, and you cannot use them. Moreover, you probably need to scan the whole OS memory to find roots for the GC. Finally, I would only trust an algorithm guaranteeing (soft) real-time GC, which would make the overhead even bigger. Reading the paper which was mentioned about Java Device Drivers on top of Linux, they just give up, and require programmers to manually free memory. They try to argue that this will not compromise safety, but I don't think their argument is convincing - it's not even clear whether they understand that Garbage Collection is needed for a safe language.

• Reflection and class loading. A full Java implementation, even when running native code, needs to be able to load new code. This is a library you can avoid, but if you have an interpreter or JIT compiler in kernel (and there's no real reason that makes it technically impossible).

• Performance. The paper about a JVM on Linux is very bad, and their performance numbers are not convincing - indeed, they test a USB 1.1 network driver, and then show that performance is not so bad! However, given enough effort something better can surely be done.

Two last things:

• I'd like to mention Singularity, which is a complete OS written in a C# variant, with just a Hardware Abstraction Layer in a native language.
• About picoJava, it's a bad idea to use it unless your system is a really memory constrained one, like a smart card. Cliff Click already explained why: it gives better performance to write a good JIT, and nowadays even smartphones can support that.