shared - i need it to be useful

[Manu]

On Mon, Oct 22, 2018 at 6:00 AM Timon Gehr via Digitalmars-d
<digitalmars-d at puremagic.com> wrote:
>
> On 22.10.18 12:26, Timon Gehr wrote:
> > ---
> > module borked;
> >
> > void atomicIncrement(int* p)@system{
> >      import core.atomic;
> >      atomicOp!("+=",int,int)(*cast(shared(int)*)p,1);
> > }
> >
> > struct Atomic(T){
> >      private T val;
> >      void opUnary(string op : "++")() shared @trusted {
> >          atomicIncrement(cast(T*)&val);
> >      }
> > }
> > void main()@safe{
> >      Atomic!int i;
> >      auto a=&[i][0];// was: Atomic!int* a = &i;
> >      import std.concurrency;
> >      spawn((shared(Atomic!int)* a){ ++*a; }, a);
> >      ++i.val; // race
> > }
> > ---
>
> Obviously, this should have been:
>
> ---
> module borked;
>
> void atomicIncrement(int*p)@system{
>      import core.atomic;
>      atomicOp!"+="(*cast(shared(int)*)p,1);
> }
> struct Atomic(T){
>      private T val;
>      void opUnary(string op:"++")()shared @trusted{
>          atomicIncrement(cast(T*)&val);
>      }
> }
> void main()@safe{
>      auto a=new Atomic!int;
>      import std.concurrency;
>      spawn((shared(Atomic!int)* a){ ++*a; }, a);
>      ++a.val; // race
> }
> ---
>
> (I was short on time and had to fix Manu's code because it was not
> actually compilable.)

Nitpick; atomicOp does not receive a shared arg under my proposal,
it's not a threadsafe function by definition as discussed a few times.