I'd have to look into it to be sure, but I think the scenario you describe may
well be possible.
However... couldn't you just put the creation/registration of the PendingFlow
*before* sending either of the commands?
-- Murphy
On Sep 12, 2011, at 7:10 AM, Zoltán Lajos Kis wrote:
> Hi,
>
> In my C++ NOX (Zaku) app I would like to make sure that a flow is installed
> on the switch. Having no better solution, I send a barrier request right
> after the flow_mod, and then wait for either an error, or a barrier reply.
> For this I register the flow_mod's and barrier's xids, and then compare
> incoming events against those. See the pseudoish code below for an example.
>
> Could someone familiar with the cooperative thread implementation in NOX tell
> me, whether it is possible that a blocking send_openflow_command() result in
> the current thread actually blocking and yielding to another one?
> Particularly in this code, can it happen that sending the flow_mod completes,
> but then the second call to send blocks, yielding to another thread. Then on
> this other thread the incoming error message is received and dispatched to
> the handler method? Resulting in the error being discarded as at that time
> the PendingFlow was not even registered…
>
> And if so, is there a way to temporarily disable this yielding, or do I
> better start making the code more complex?
>
> Thank you,
> Zoltan.
>
>
> ------------------------------
>
>
> struct PendingFlow {
> uint32_t modXid;
> uint32_t barrierXid;
> ...
> }
>
> class Example {
>
> PendingFlow *pendingFlow;
> ...
>
> void
> Example::install_flow(ofp_flow_mod *mod) {
> ofp_header *barrier = make_barrier();
>
> mod->header->xid = generate_xid();
> barrier->xid = generate_xid();
>
> send_openflow_command(pi.datapath_id, &mod->header, true);
> send_openflow_command(pi.datapath_id, barrier, true);
>
> pendingFlow = new PendingFlow(mod->header->xid, barrier->xid);
> ...
> }
>
>
> Disposition
> Example::handleError(const Event &e) {
> const Error_event& err = assert_cast<const Error_event&>(e);
>
> if (pendingFlow != NULL && pendingFlow.modXid == getErrorXid(err)) {
> delete pendingFlow; pendingFlow = NULL;
> // Process error
> }
> …
> return CONTINUE;
> }
>
> Disposition
> Example::handleBarrier(const Event &e) {
> const Barrier_reply_event& barrier = assert_cast<const
> Barrier_reply_event>(e);
>
> if (pendingFlow != NULL && pendingFlow.barrierXid ==
> getBarrierXid(barrier)) {
> delete pendingFlow; pendingFlow = NULL;
> // Process completion
> }
> ..
> return CONTINUE;
> }
>
> …
> }
>
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