[Issue 1282] Very strange GC problem, memory corruption

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=1282


deewiant at gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |INVALID




------- Comment #4 from deewiant at gmail.com  2007-06-21 03:29 -------
I found the problem, and it's my code: I'm deleting a pointer to a struct which
hasn't been allocated with new. It's a remnant from when I used a class instead
of a struct. It boils down to the following:

struct S {}
S* ps;

void main() {
        S s;
        ps = &s;
        delete ps;

        // assign ps to something else and keep doing stuff...
}

http://www.digitalmars.com/d/expression.html#DeleteExpression says: "If the
garbage collector was not used to allocate the memory for the instance,
undefined behavior will result."

I can't reproduce the problem after removing the delete, so I'll assume that
was it: the GC allocates memory for a char[] array on top of
deleted-but-not-newed memory, which happens to be on top of a class reference
in a struct. This would explain why the class reference becomes 0xffffffff
instead of, say, null: char.init is 0xff.

Those Access Violations would just be harder-to-find symptoms of the same.

Of course, if I'm unlucky, something else causes the problem and the delete is
just one of those unrelated, yet relevant, lines, but I don't think so.

My bad! Nothing to see here!

Unless there's a way for the GC to stop this from ever happening accidentally?
Couldn't it know which areas in memory it has allocated?


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