s4: Composite async callback on error conditions

[Volker Lendecke]

On Sat, Jan 15, 2011 at 10:12:35PM +0100, Matthias Dieter Wallnöfer wrote:
> Given the file "libcli/composite/composite.c":
> >_PUBLIC_ void composite_error(struct composite_context *ctx,
> >NTSTATUS status)
> >{
> >        /* you are allowed to pass NT_STATUS_OK to
> >composite_error(), in which
> >           case it is equivalent to composite_done() */
> >        if (NT_STATUS_IS_OK(status)) {
> >                composite_done(ctx);
> >                return;
> >        }
> >        if (!ctx->used_wait && !ctx->async.fn) {
> >                event_add_timed(ctx->event_ctx, ctx,
> >timeval_zero(), composite_trigger, ctx);
> >        }
> >        ctx->status = status;
> >        ctx->state = COMPOSITE_STATE_ERROR;
> >        if (ctx->async.fn != NULL) {
> >                ctx->async.fn(ctx);
> >        }
> >}
> Regardless if an action succeeds (composite_done branch) or fails a
> specified async callback is launched if it has been set. As far as I
> can see this leads to problems: see http://build.samba.org/build.cgi/build/50b21d3db7ff575c3bdac41bedc8d77ab74680a9
> (access in talloc destructor).
> So my question: should we still be running async callbacks also on
> failure conditions? Or can this particular problem be solved
> differently?

While I don't know the current problem at hand, and I
haven't really looked at the composite async programming
variant for a while, let me comment from the tevent_req
perspective (which I think is very similar to the composite
one): Yes, you do want to run the async callbacks in the
error case. The caller of the composite async process needs
to be given a chance to detect the error by calling some
form of _recv function. If you don't call the async
function, the caller has no chance to take an appropriate
action like a fallback to something different.

With best regards,

Volker

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