Sharing in D

[Walter Bright]

downs wrote:
> Walter Bright wrote:
>> Steven Schveighoffer wrote:
>>> I would hazard to guess that adopting this would cause a larger
>>> rift than const.
> He's probably right.

A couple years ago, I was in a room with 30 of the top C++ programmers 
in the country. The topic was a 2 day conference on how to support 
multithreading in C++. It soon became clear that only two people in the 
room understood the issues (and I wasn't one of them).

I think I understand the issues now, but it has taken a long time and 
repeatedly reading the papers about it. It is not simple, and it's about 
as intuitive as quantum mechanics.

I suggested to Andrei and Bartosz just the other day that I don't expect 
the value in this model will be readily apparent. I'm pretty sure it 
won't be, as the issues are hard to understand. But the issues being 
hard to understand is exactly why this model is needed. There are surely 
several articles, papers, and tutorials in this :-)


>> Perhaps. But the alternative is the current wild west approach to 
>> multithreaded programming. With the proliferation of multicore 
>> computers, the era where this is acceptable is coming to an end.
> 
> Since when is it the language's job to tell us what's acceptable and
> what's not?

I meant that programmers will no longer find the language acceptable if
it doesn't offer better support.


>> But still, you're far better off than the current wild west
>> approach where everything is implicitly shared with no protection
>> whatsoever. The popular double checked locking bug will be
>> impossible to code in D without stuffing in explicit casts. The
>> casts will be a red flag that the programmer is making a mistake.
> 
> The double checked locking "bug" is only a bug on certain
> architectures, none of which D is supported on.

D is not only meant to be more than an x86 only language, the x86 family 
steadily moves towards the relaxed sequential consistency model. The 
threading model supported by Java and the upcoming C++0x release are 
both based on the relaxed model, that is clearly where the industry 
expects things to go, and I see no reason to believe otherwise.