Are structs saved in multi-thread delegate call?

[Ramon via Digitalmars-d-learn]

mmm, I figured the problem, but don't know how to solve it.
my struct has a destructor which clears itself:

struct json_value
{
   ~this() { .ValueClear(&data); }
}

so how I can I put a struct in the heap? (not in the stack, as is 
the default..)