[dmd-concurrency] shared arrays, real, shared classes, synchronized classes

[Kevin Bealer]

On Fri, Jan 29, 2010 at 6:03 PM, Andrei Alexandrescu <andrei at erdani.com>wrote:

> Walter and I just talked over the phone and agreed on the following. Of
> course the decisions are not final and are up for debate.
>
> 1. Atomic array assignment is in.
>
> We discussed that and concluded the following:
>
> * CMPXCHG16B and friends are the norm of modern Intel-like machines, and
> are unlikely to go away soon. We are designing D for the future and the
> future looks like two-word assignment is in it.
>
> * Pre-2004 AMDs and probably some other chips still lack two-word
> assignment. We decided that we will look for creative solutions to those
> problems as they come up (hat tip to Kevin's idea of using a spin lock).
>
> 2. Atomic assignment of real is still undecided.
>
> I think I'll write in TDPL that it's platform dependent. Assignment to
> 80-bit reals on 32-bit machines is still problematic.
>
> 3. There are _no_ more synchronized or shared methods. That is, code like
> this is incorrect:
>
> class A { void fun() shared { } }
> class B { void fun() synchronized { } }
>
> Rationale: it is tenuous to offer mixed modes in the same class.
>
> 4. The "synchronized" attribute is hoisted at class level:
>
> synchronized class A { ... }
>
> That means each and every method of that class is synchronized.
>
> 5. The "shared" attribute is hoisted at class or struct level:
>
> shared class A { ... }
> shared struct B { ... }
>
> That means the implementation is lock-free and uses its own synchronization
> mechanisms.
>
> 6. When defining an object of a synchronized of shared type, you still need
> to qualify it with "shared" in order to make it so. For example:
>
> synchronized class A { ... }
> shared A a; // fine
> A b;        // error
>
> (I'm not 100% sure about this.)
>
> ====================
>
> These rules will simplify and modularize concurrent code. With message
> passing, synchronized classes, and shared objects, I hope we get to put
> together a solid concurrency offering in D2. Please share your thoughts.
>
>
> Andrei
>

I like it.

Kevin
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