Messages in this thread | | | Date | Sat, 1 Dec 2007 00:19:50 +0100 | From | "J.A. Magallón" <> | Subject | Re: Kernel Development & Objective-C |
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On Fri, 30 Nov 2007 11:29:55 +0100, "Loïc Grenié" <loic.grenie@gmail.com> wrote:
> 2007/11/29, Ben Crowhurst <Ben.Crowhurst@stellatravel.co.uk>: > > Has Objective-C ever been considered for kernel development? > > > > regards, > > BPC >
Well, I really would like to learn some things here, could we keep this off-topic thread alive just a bit, please ? (I know, I'm going to gain a troll's fame because I can't avoid this discussions, its one of my secret vices...)
> No, it has not. Any language that looks remotely like an OO language > has not ever been considered for (Linux) kernel development and for > most, if not all, other operating systems kernels. >
I think BeOS was C++ and OSX is C+ObjectiveC (and runs on an iPhone). Original MacOS (fron 6 to 9) was Pascal (and a mac SE was very near to embedded hardware :) ).
I do not advocate to rewrite Linux in C++, but don't say a kernel written in C++ can not be efficient.
> Various problems occur in an object oriented language. One of them > is garbage collection: it provokes asynchronous delays and, during > an interrupt or a system call for a real time task, the kernel cannot > wait.
C++ (and for what I read on other answer, nor ObjectiveC) has no garbage collection. It does not anything you did not it to do. It just allows you to change this
struct buffer *x; x = kmalloc(...) x->sz = 128 x->buff = kmalloc(...) ... kfree(x->buff) kfree(x)
to struct buffer *x; x = new buffer(128); (that does itself allocates x->buff, because _you_ programmed it, so you poor programmer don't forget) ... delete x; (that also was programmed to deallocate x->buff itself, sou you have one less memory leak to worry about)
> Another is memory overhead: all the magic that OO languages > provide take space in memory and Linux kernel is used in embedded > systems with very tight memory requirements. >
An vtable in C++ takes exactly the same space that the function table pointer present in every driver nowadays... and probably the virtual method call that C++ does itself with
thing->do_something(with,this)
like push thing push with push this call THING_vtable+indexof(do_something) // constants at compile time
is much more efficient that what gcc can mangle to do with
thing->do_something(with,this,thing)
push with push this push thing get thing+offsetof(do_something) // not constant at compile time dereference it call it
(that is, get a generic field on a structure and use it as jump address)
In short, the kernel is object oriented, implements OO programming by hand, but the compiler lacks the knowledge that it is object oriented programming so it could do some optimizations.
> Lots of people will think of better reasons why ObjC is not used...
People usually complains about RTTI or exceptions, but benefits versus memory space should be seriously considered (sure there is something in current drivers to ask 'are you a SATA or an IDE disk?').
-- J.A. Magallon <jamagallon()ono!com> \ Software is like sex: \ It's better when it's free Mandriva Linux release 2008.1 (Cooker) for i586 Linux 2.6.23-jam03 (gcc 4.2.2 (4.2.2-1mdv2008.1)) SMP Sat Nov 09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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