[OneMoreIdol]

Outside of userland tasks like file manipulation, it is impractical to use the popular web application languages like Java or scripting languages such as Javascript or PHP or Python for systems programming without employing interfaces or hooks to libraries or programs written in languages that are compiled to machine code, simply because programs in those languages are commonly deployed using virtual machines or interpreters that have only userland privileges. So good luck writing a driver. And I don't know ... if your vm has heap allocated to it, are you able to address system memory out side of that to address hardware? Also, the language runtimes usually add a lot of overhead as well and employ automatic garbage collection, which is generally something you don't want in performance-critical systems.

[justincormack]

That is not strictly true. Look at Snabb switch, written almost entirely in LuaJIT for example https://github.com/SnabbCo/snabbswitch - you need some kind of ffi to mmap device memory, but it is quite possible. (LuaJIT is fast of course which helps for 10Gb ethernet).

[OneMoreIdol]

That's kinda what I was thinking when I commented, and there are sure to be exceptions. But I don't see anything different with your Snabb switch example. You can probably use Java and JNI for that matter to call mmap, but would you be able to write an implementation of mmap in LuaJIT ?

[justincormack]

Yes you can call mmap with the ffi in LuaJIT just fine. It is not very complicated, it just asks the kernel to do it. Implementing what the kernel does, well that does need some assembly.

[OneMoreIdol]

Indeed we agree. Using any ffi for that matter.