[Issue 12795] New: atomicLoad allows unsafe removal of shared from class references

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=12795

          Issue ID: 12795
           Summary: atomicLoad allows unsafe removal of shared from class
                    references
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P1
         Component: druntime
          Assignee: nobody at puremagic.com
          Reporter: kirsybuu at gmail.com

Tested with dmd v2.066-devel-ca213d2

---

struct Struct {
    int x;
}
class Class {
    int x;
}
void main() {
    import core.atomic;

    shared(Struct*) si = new shared Struct;
    shared(Struct)* i = atomicLoad(si);     // Safe as expected

    shared(Class) sd = new shared(Class)();
    Class d = atomicLoad(sd);               // Unsafe!
}

---

To find out what went wrong, I copied the definition of atomicLoad and modified
it as such:

---

template HeadUnshared(T) {
    static if( is( T U : shared(U*) ) )
        alias shared(U)* HeadUnshared;
    else
        alias T HeadUnshared;
}

HeadUnshared!(T) atomicLoad(T)( ref const shared T val ) nothrow {
    pragma(msg, "typeof(val) == " ~ typeof(val).stringof);
    pragma(msg, "T == " ~ T.stringof);
    pragma(msg, "typeof(return) == " ~ typeof(return).stringof);

    return typeof(return).init;
}

---

And the output is:

typeof(val) == shared(const(Struct*))
T == shared(Struct)*
typeof(return) == shared(Struct)*

typeof(val) == shared(const(Class))
T == Class
typeof(return) == Class

--