On Tue, Aug 27, 2013 at 05:46:40PM +0200, deadalnix wrote:
> On Tuesday, 27 August 2013 at 14:26:53 UTC, H. S. Teoh wrote:
> >What if move(r2) throws? Then res1 won't get cleaned up, because r1
> >has already been nulled by the move.
> >
>
> I don't think move can throw.
Well, it's not marked nothrow, so I wouldn't count on that.
Also, the fact that move() uses memcpy is a bit worrying; Adam Ruppe &
myself ran into a nasty bug involving closures over struct members when
the struct may get moved upon return from a function. For example:
struct S {
int id;
void delegate()[] cleanups;
this() {
id = acquireResource();
cleanups ~= {
// N.B.: closure over this.id
releaseResource(id);
};
}
}
S makeS() {
// Problem: S.cleanups[0] is a closure over the struct
// instance on this function's stack, but once S is
// returned, it gets memcpy'd into the caller's stack
// frame. This invalidates the delegate's context
// pointer.
return S(1);
}
void main() {
auto s = makeS();
// Problem: s.cleanups[0] now has an invalid context
// pointer. If the stack is reused after this point, the
// dtor of s will get a garbage value for s.id.
}
Using move() to move a resource from a local variable into a member
looks like it might be vulnerable to this bug as well -- if the resource
has closures over member variables it might trigger this problem.
T
--
To provoke is to call someone stupid; to argue is to call each other stupid.
