[Info-vax] Rust as a HS language, was: Re: Quiet?

[Arne Vajhøj]

On 4/5/2022 8:41 PM, Dan Cross wrote:
> In article <624cd4e1$0$701$14726298 at news.sunsite.dk>,
> Arne Vajhøj  <arne at vajhoej.dk> wrote:
>> Rust checks memory access *unless* in an unsafe block (idea borrowed
>>from C# language). As a low level language Rust has the need to be able
>> to do some flexible memory access - I can not imagine it is
>> possible to write a device driver if only able to access memory
>> in variables in the program.
> 
> It's possible if you are willing to play games with the linker,
> and very early bootstrap, but it's sufficiently tedious that it
> is just much easier to transmute an integer to a pointer via
> unsafe.  Noteably, you really only have to do that once, and you
> can largely confine _most_ drivers to mostly safe code.
> 
> I don't think that Rust's unsafe was inspired by C#, but I
> confess I haven't asked.

I don't know for sure.

But it seems a bit unlikely that they by coincidence chose
the exact same construct.

unsafe {
     ...
}

>> Rust has a unique approach to memory handling based on
>> ownership (idea borrowed from modern C++ best practice
>> not C++ language) that avoids memory leaks without GC - as
>> a low level language that may be used in real time
>> context, then the standard solution to avoid memory
>> leaks in high level languages GC could be problematic.
> 
> Yup.  You get something _very_ close to managed memory without
> the overhead of GC.  Note that sometimes GC can be surprisingly
> helpful in high-overhead situations (think tight loops where,
> thanks to GC, you don't have to check ref counts or pointer
> validity...), but generally you get much of that in Rust without
> the additional overhead.

Despite what many think then the problem with GC is not
overhead. Often GC is as efficient or even more efficient
than manual deallocation.

The problem with GC is the poor real time characteristics.
It tend to give small pauses at non-deterministic point.

Arne