Re: Kernel Development & Objective-C

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On Nov 30, 2007, at 09:34:45, Lennart Sorensen wrote:
On Thu, Nov 29, 2007 at 12:14:16PM +0000, Ben Crowhurst wrote:
Has Objective-C ever been considered for kernel development?

Doesn't objective C essentially require a runtime to provide a lot of the features of the language? If it does (as I suspect) then it is totally unsiatable for kernel development.

That and object oriented languages in general are badly designed and a bad idea. Having not used objective C I have no idea if it qualifies as badly designed or not. Certainly C++ and java are both very badly designed.

Objective-C is actually a pretty minimal wrapper around C; it was originally implemented as a C preprocessor. It generally does not have any kind of memory management, garbage collection, or anything else (although typically a "runtime" will provide those features). There are no first-class exceptions, so there would be nothing to worry about there (the exceptions used in GUI programs are built around the setjmp/longjmp primitives). Objective-C is also almost completely backwards-compatible with C, much more so than C++ ever was. As far as the runtime goes the kernel would be expected to write its own, the same way that it implements "kmalloc()" as part of a "C runtime". Since the runtime itself never does any implicit memory allocation, I think it would conceivably even be relatively safe for kernel usage.

With that said, there is a significant performance penalty as all Objective-C method calls are looked up symbolically at runtime for every single call. For GUI programs where large chunks of the code are event-loops and not performance-sensitive that provides a huge amount of extra flexibility. In the kernel though, there are many codepaths where *every* *single* instruction counts; that could be a serious performance hit.

Cheers,
Kyle Moffett

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