🚀 go-pugleaf

In article <1367@taniwha.UUCP> paul@taniwha.UUCP (Paul Campbell) writes:
> I once implemented a complete port of Unix that ran within a single VMS
> process, the Unix kernel ran in a VMS process in supervisor mode, it ran
> multiple Unix processes in user mode, supervisor mode ASTs were used for
> Unix 'interrupts' (for example for input characters from terminals, disk
> IO completeions etc etc)

Sounds reasonable. I'd hate to think of doing it the opposite way.

> >Much of the *C* run-time in *any* language is non-reentrant, and I would
> >be surprised if the VMS library was any better. If I get an AST while I'm

> Yeah this is a major design flaw in the Unix/C world - an operating system
> that returns more than 1 thing from its system calls is implemented in
> a language that only returns 1 thing from a call.

That's not the problem. The problem is that there's all sorts of internal
state. You mention errno, but that's the least of it. What about the internal
contents of io buffers? How do you resolve that? You either abandon user
level buffering (no thanks), or you put a semaphore around every library
call, or you defer ASTs while in the runtime. That means you get unpredictable
I/O delays (how long does a read from a serial port take? Could be days), or
the chance of deadlocks (call printf or WRITE(6,*) in an AST called while
in a previous call to the same routine). Errno is an easy one!

	sigio()
	{
		int save_errno = errno;
		do your own I/O.
		errno = save_errno;
	}

> This doesn't mean that
> C shouldn't have been used for Unix - just that the API should have been 
> designed differently for example:
> 
> 	(act_len, errno) = read(file, data, len);
> 
> probably should have been done as:
> 
> 	errno = read(file, data, len, &act_len);

I like:

	token = syscall(args);
	status = get_status(token);
	result = get_result(token);
	discard(token);

Where token is an opaque object. Much more versatile.
-- 
Peter da Silva                                            `-_-'
Ferranti International Controls Corporation                'U` 
Sugar Land, TX  77487-5012 USA
+1 713 274 5180                            "Zure otsoa besarkatu al duzu gaur?"