0xC0000005: 0x0000000000000000 access violation...

[Simen Kjærås]

On Sunday, 1 July 2018 at 22:04:05 UTC, Robert M. Münch wrote:
> On 2018-07-01 09:05:56 +0000, Robert M. Münch said:
>
>> This one look nasty...
>
> And it was... the problem was, that I kept D allocated pointers 
> in C code without informing the GC that the memory can't be 
> collected nor moved. Bridging from D to C and back, is pretty 
> tricky to not miss any allocated memory.
>
> Couldn't such a problem be mitigated with an annotation like 
> @externalRef or so, which would add the code to protect such 
> memory from being GC? It would make the code much more explicit.

An annotation probably won't do it. This might:

     struct ExternalRef(T) {
         T* ptr;
         alias ptr this;

         void free() {
             import core.stdc.stdlib : free;
             free(ptr);
         }
     }

     auto externalRef(T)() {
         import core.stdc.stdlib : malloc;
         return ExternalRef!T(cast(T*)malloc(T.sizeof));
     }

     extern(C)
     void sendToC(ExternalRef!int p);
     extern(C)
     ExternalRef!int getFromC();

     unittest {
         sendToC(externalRef!int());
         getFromC().free();
     }

This is hardly a production-quality piece of code, but should 
give some ideas for what's possible.

--
   Simen