[zeromq-dev] lost message due to EINTR

[Pieter Hintjens]

Can you make a minimal reproducible test case?

On Fri, Jan 9, 2015 at 9:41 AM,  <sven.koebnick at t-online.de> wrote:
> another related thing buthers me in this context:
>
> When zmsg_send() indeed returns with rc==-1 and a NULLed message (data is
> definitely lost) I have a chance to check for this lost message (simply
> asserting on rc==-1 && message==NULL).
>
> BUT (!!) what is with zmsg_recv() ? Situation: I successfully zmsg_send() a
> message and is is delivered by ZMQ to the target (still inside ZMQ). When
> the same error occurs in the applications zmsg_recv() call, will the message
> be returned in the next call to zmsg_recv() or is is lost in this case also.
> Here, I do not have any chance to work with a copy as would be possible in
> the sending example below.
>
> This question destroys the first idea of holding a copy before sending.
> Indeed, I tryed, but zmsg_dup() destroyes routing information in the
> message, so it gets lost(silently) in transport failing to be adressed. Does
> zmq_msg_copy() work "better" and also copies the rotuing info?
>
> As an info: the EINTR thingy happens in Suse Linux on 32 and 64 bit using
> ZMQ4 (in any version) while debuging with Eclipse/gdb. I happens VERY often
> when breakpoints are triggered, but also (rarely) when the application is
> just running under gdb without any suspends due to breakpoints (breakpoints
> existing, but not hit).
>
>
>
> The system when pretty well for 2 years (!!!) under ZMQ2 and I have this
> problem only in ZMQ4 ... there has never been an EINTR under ZMQ2, so my
> code had to be heavily modified with loops for "temporary failures" with
> errno== EINTR or EAGAIN.
>
>
>
> ^5
>
>
>
> Am 2015-01-09 08:30, schrieb sven.koebnick at t-online.de:
>
> Hi * !
>
> I recently switched from ZMQ2 (pretty old) to ZMQ 4 and since then have some
> problems in debugging with EINTR.
>
> Following code:
>
>                                 do {
>                                     rc = zmsg_send (&zrep, clsocket_);
>                                     if (rc<0) {
>                                         if (errno == EINTR || errno ==
> EAGAIN) {
>                                             logWarn("temporary failure in
> zmq send() ... will be tried again.");
>                                         } else {
>                                             logFatal("hard error in sending
> zmq ... manually destroying message ... it will be lost");
>                                             zmsg_destroy(&zrep);
>                                         }
>                                         if (zrep) {
>                                             logWarn("sending of reply msg
> returned rc("<<rc<<"), zmq_errno("<<zmq_errno()<<")
> "<<zmq_strerror(zmq_errno()));
>                                             logWarn("but message is still
> existent ... retrying");
>                                         } else {
>                                             logError("sending of reply msg
> returned rc("<<rc<<"), zmq_errno("<<zmq_errno()<<")
> "<<zmq_strerror(zmq_errno()));
>                                             logFatal("message nulled anyway
> by zmq ... seems lost ...");
>                                         }
>                                     }
>                                 } while (zrep); // repeat until message is
> gone
>
> This snippet usualy works, but sometimes I get the warning of EINTR. No
> problem, I thought, but despite returning an error (rc==-1, errno==EINTR)
> the message pointer is NULLed, so I cannot resend the message.
>
> The Logs prove, that indeed the message is NOT sent, and for resending I'd
> need a copy ... what am I doing wrong?
>
>
>
> ^5
>
> sven
>
>
>
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