shared - i need it to be useful

[rikki cattermole]

On 21/10/2018 10:41 PM, Manu wrote:
> On Sun., 21 Oct. 2018, 2:05 am Walter Bright via Digitalmars-d, 
> <digitalmars-d at puremagic.com <mailto:digitalmars-d at puremagic.com>> wrote:
> 
>     On 10/20/2018 11:30 AM, Manu wrote:
>      > You can write an invalid program in any imaginable number of ways;
>      > that's just not an interesting discussion.
> 
>     What we're discussing is not an invalid program, but what guarantees
>     the type
>     system can provide.
> 
>     D's current type system guarantees that a T* and a shared(T)* do not
>     point to
>     the same memory location in @safe code.
> 
> 
> My proposal guarantees that too, but in a more interesting way, because 
> it opens the door to a whole working model. And it's totally @safe.
> 
>     To get them to point to the same memory location, you've got to dip
>     into @system
>     code, where *you* become responsible for maintaining the guarantees.
> 
> 
> My model preserves that property. Why do you think I'm running that 
> static guarantee?
> 
> It's all irrelevant if you don't express any mechanism to *do* anything. 
> Shared today does not have any use. It simply expresses that data *is* 
> shared, and says nothing about what you can do with it.
> If you don't express a safe mechanism for interacting with shared data, 
> then simply expressing the distinction of shared data really is 
> completely uninteresting.
> It's just a marker that's mixed up in a bunch of unsafe code. I'm no 
> more satisfied than I am with C++.
> 
> Shared needs to do something; I propose that it strictly models 
> operations that are threadsafe and semantic restrictions required to 
> support that, and then you have a *usage* scheme, which is safe, and API 
> conveys proper interaction.. not just an uninteresting marker.
> 
> I'm genuinely amazed that you're not intrigued by a @safe shared 
> proposition. Nobly likes @safe more than you.
> 
> I could run our entire SMP stack 100% @safe.
> 
> I am going to fork D with this feature one way or another. It's the most 
> meaningful and compelling opportunity I've seen in ever. If there's ever 
> been a single thing that could truly move a bunch of C++ programmers, 
> this is it. C++ can do a crappy job of modelling most stuff in D, but it 
> simply can't go anywhere near this, and I've been working on competing 
> C++ models for months.
> SMP is the future, we're going all-in this generation. Almost every 
> function in our codebase runs in an SMP environment... And I was 
> staggered that I was able to work this definition through to such a 
> simple and elegant set of rules.
> I can't get my head around why people aren't more excited about this... 
> fully @safe SMP is huge!

I'm excited, but you need to write a DIP even if preliminary which shows 
both new semantics but also shows both working and current code to 
compare them.