socket.send() depends on the socket type. If it’s a drop socket (router, pub) it will drop the message. If it’s one of the others, it will queue the message.
On Dec 6, 2013, at 16:15, artemv zmq <[email protected]> wrote: > Thanks Justin. > > But still following points remain unanswered: > - why socket.send() returns "true" when sending to unexisting peer > (socket.hwm=0) ? > - why poller.pollout() returns "true" (socket registered on POLLOUT) when > polling socket which is connected to unexisting peer ? > > For the first case: either prohibit 0 as an argument value or please bring a > light on expected behaviour. For second -- such "polling" looks strange, > isn't? > > > BR > -artemv > > > > > 2013/12/6 Justin Cook <[email protected]> > Artem, > > The “high-water mark” is simply used to prevent memory exhaustion: > > "It has ways of dealing with over-full queues (called "high water mark"). > When a queue is full, ØMQ automatically blocks senders, or throws away > messages, depending on the kind of messaging you are doing (the so-called > "pattern”).” > > It has nothing to do with with specific peers. What you are doing is setting > the HWM to a low number and then hoping for a send() to block — not return > false — if the queue is exhausted. You then assume that a peer is down if you > were to block. Given that the behaviour differs based on the messaging > pattern you are using, you will need to setup a test case. > > If I were you, I would abandon this idea and investigate what Pieter said > @1311. Sequence numbering and NACKs is what I would look at. > > Once you have done that, feel free to generate a test case and share with us > on the list. > > -- > Justin Cook > > > On Friday, 6 December 2013 at 13:59, artemv zmq wrote: > > > Thanks Pieter. All this sounds new to me ... :| > > > > But if we return to HWM question -- when I set hwm=0 and sending to > > unexistent peer, then every .send() call return me "true". Is not this an > > issue in ZMQ core? > > > > > > BR > > -artemv > > > > > > > > 2013/12/6 Pieter Hintjens <[email protected] (mailto:[email protected])> > > > You should probably think about a mix of sequence numbering, credit > > > based flow control and negative acks that flow asynchronously against > > > the message flow. You can then send without waiting, ensure you never > > > overrun buffers, and catch errors if they happen. > > > > > > On Fri, Dec 6, 2013 at 2:02 PM, artemv zmq <[email protected] > > > (mailto:[email protected])> wrote: > > > > 2Matt: > > > > > > > > > > Sending a message may take some time (connection latency, etc) so > > > > > > how > > > > > > long do you think it will take to send the message before you > > > > > > assume it has > > > > > > been sent or not? > > > > > > > > > > > > > Sure thing -- I can go with some reasonable timeout specified via > > > > properties/cmdline. Not a problem. > > > > > > > > > > If you want send() to return false > > > > The only way I found ZMQ can give me false on .send() -- is to set hwm=1 > > > > and send two messages everytime: > > > > > > > > --send_dummy_scout_msg--> > > > > --send_bet_msg--> > > > > --send_dummy_scout_msg--> > > > > -- X > > > > > > > > Got idea? If "dummy_scout" stucked in a queue, then "bet_msg" will not > > > > be > > > > sent , so .send() will return me "false". Pretty stupid... Not sure I > > > > can > > > > seriously explain this to chief architects :) Is there other way? > > > > > > > > > > > > > > > > 2013/12/6 Diego Duclos <[email protected] > > > > (mailto:[email protected])> > > > > > > > > > > If ALL you need is to know is "has message left NIC on sending > > > > > process or > > > > > not", there is a socket option for that. It's called > > > > > ZMQ_ROUTER_MANDATORY. > > > > > > > > > > > > > > > On Fri, Dec 6, 2013 at 1:07 PM, Matt Connolly <[email protected] > > > > > (mailto:[email protected])> > > > > > wrote: > > > > > > > > > > > > Could you use the socket monitoring to check the connected state of > > > > > > the > > > > > > dealer socket? > > > > > > > > > > > > Sending a message may take some time (connection latency, etc) so > > > > > > how > > > > > > long do you think it will take to send the message before you > > > > > > assume it has > > > > > > been sent or not? > > > > > > > > > > > > If you want send() to return false, you would need it to be a > > > > > > blocking > > > > > > synchronous call which against the idea of queuing messages to be > > > > > > sent (as > > > > > > far as I understand) > > > > > > > > > > > > Good luck > > > > > > > > > > > > Cheers, > > > > > > Matt. > > > > > > > > > > > > On 6 Dec 2013, at 9:19 pm, artemv zmq <[email protected] > > > > > > (mailto:[email protected])> wrote: > > > > > > > > > > > > Sorry for confusion. > > > > > > > > > > > > When I said out-of-control -- I meant they do have ZMQ but they may > > > > > > have > > > > > > different release cycle and QoS. It's just a service on ZMQ, on a > > > > > > ROUTER. > > > > > > > > > > > > Our application is aimed to take a message, get its headers, decide > > > > > > on > > > > > > what service ROUTER to send and that's it. W/o waiting for reply. > > > > > > Essentially we are a DEALER. > > > > > > Replies are important, but as long as they coming back. If they > > > > > > not. Not > > > > > > a problem. Client application (iPhone game) by itself checking > > > > > > replies and > > > > > > correlation, > > > > > > and keep watching: "ahha, I didn't receive ack for betting. hmmm. > > > > > > Let's > > > > > > try again". Now it's more clear? > > > > > > > > > > > > I really don't need PUB/SUB. I need DEALER/ROUTER. Here, in my > > > > > > company, > > > > > > the only biggest concern so far with ZMQ -- misleading behaviour: > > > > > > when .send() returns "true" that should mean that message "sent", > > > > > > whatever that means: left our PID, left our NIC and so on, we have > > > > > > to > > > > > > guarantee that message is not on us. > > > > > > I know what's PUB/SUB. And again, telling you that it's not > > > > > > suitable. The > > > > > > problem statement is simple: > > > > > > > > > > > > - don't use HWM for DEALER/ROUTER (prohibit message queueing). > > > > > > - raise immediately if you can't .send() (don't collect in internal > > > > > > queue) > > > > > > > > > > > > > > > > > > Is it possible? > > > > > > > > > > > > > > > > > > BR > > > > > > -artemv > > > > > > > > > > > > > > > > > > 2013/12/6 Justin Cook <[email protected] (mailto:[email protected])> > > > > > > > > > > > > > > Ok, this is confusing. If you are sending a message to a service > > > > > > > that is > > > > > > > out of your control, either they use 0MQ or not. I assume they do > > > > > > > not. If > > > > > > > that’s the case, it should not be a part of the use case. > > > > > > > > > > > > > > You say you need to know if a message has been received. But, > > > > > > > then you > > > > > > > say no ACKs or timeouts. I’m even more confused. If you are > > > > > > > making a request > > > > > > > to a foreign service over — I assume — HTTP which uses TCP, you > > > > > > > are very > > > > > > > well getting HTTP return codes with the TCP session doing all the > > > > > > > hard work. > > > > > > > You already have what you are looking for there. > > > > > > > > > > > > > > As far as your system — going out to mobile devices — using > > > > > > > PUB/SUB and > > > > > > > ACKing messages, this is something you will have to do in another > > > > > > > channel > > > > > > > with 0MQ. Multicast uses UDP; because, it is not feasible to send > > > > > > > TCP ACKs > > > > > > > from every single subscriber. It’s simply not scalable. > > > > > > > > > > > > > > You very well may need to develop your own application protocol > > > > > > > to send > > > > > > > ACKs or the publisher retransmits. I highly suggest you have a > > > > > > > look at this: > > > > > > > > > > > > > > > > > > > > > http://stackoverflow.com/questions/12956685/what-are-the-retransmission-rules-for-tcp > > > > > > > > > > > > > > It may be something you will want to mimic in your implementation. > > > > > > > Someone else has already suggested a timeout for resending > > > > > > > unacknowledged > > > > > > > messages. As you can see, this is one of the ways TCP > > > > > > > retransmissions work. > > > > > > > You also may have corrupt data that fail a CRC or hash. > > > > > > > > > > > > > > I will finish by saying that if you do have a PUB/SUB design using > > > > > > > another channel for unicast communication, you will need to be > > > > > > > very aware of > > > > > > > scalability issues. You may need to use a lockstep pattern such > > > > > > > as REQ/REP > > > > > > > if you need guarantee of communication. > > > > > > > > > > > > > > -- > > > > > > > Justin Cook > > > > > > > > > > > > > > > > > > > > > On Friday, 6 December 2013 at 09:46, artemv zmq wrote: > > > > > > > > > > > > > > > Thanks for heads up. > > > > > > > > > > > > > > > > 2crocket: > > > > > > > > No acks. No timeouts. Nothing should be kept. Messages should > > > > > > > > just > > > > > > > > flowing back and forth. But for every message we have to answer > > > > > > > > a question: > > > > > > > > "has message left NIC on sending process or not". Let me give > > > > > > > > example with > > > > > > > > betting: game on iPhone sending us a message "make-a-bet", then > > > > > > > > we send this > > > > > > > > to BettingService which isn't in our control, > > > > > > > > so all we have to guarantee -- "make-a-bet" message has left > > > > > > > > our NIC > > > > > > > > and been "sent" to BettingService. If "make-a-bet" has been > > > > > > > > droped on a > > > > > > > > network - ok, if BettingService itself drops it - ok. > > > > > > > > > > > > > > > > Back to HWM. Let's consider that we send to unavaliable peer. > > > > > > > > hwm=1. It means you can send 1 message "blindly" and .send() > > > > > > > > function > > > > > > > > returns success. Of course sending second time will fail. > > > > > > > > But... the trick > > > > > > > > is -- we need answer first time. > > > > > > > > hwm=0. It means you can send any number of messages and .send() > > > > > > > > function _always_ returns success :(( Again, isn't this a bug? > > > > > > > > > > > > > > > > > > > > > > > > So let me re-phrase the original question -- how to fail at > > > > > > > > .send() > > > > > > > > function in ZMQ? > > > > > > > > > > > > > > > > > > > > > > > > BR > > > > > > > > -artemv > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > 2013/12/6 crocket <[email protected] > > > > > > > > (mailto:[email protected]) > > > > > > > > (mailto:[email protected])> > > > > > > > > > Why don't you set a timeout for asynchronous ACKs? > > > > > > > > > You receive ACKs asynchronously and keep associated messages > > > > > > > > > until > > > > > > > > > ACKs come or a timeout occurs. > > > > > > > > > A timeout of 20 seconds is a reasonable estimate. > > > > > > > > > After a timeout, if a message doesn't have a corresponding > > > > > > > > > ACK, it > > > > > > > > > is determined that the message wasn't delievered, and the > > > > > > > > > message is sent > > > > > > > > > again or discarded. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Fri, Dec 6, 2013 at 3:19 AM, artemv zmq > > > > > > > > > <[email protected] (mailto:[email protected]) > > > > > > > > > (mailto:[email protected])> wrote: > > > > > > > > > > Hi, > > > > > > > > > > > > > > > > > > > > My name is Artem. I stay with ZMQ (on java) a year or so. > > > > > > > > > > Got a > > > > > > > > > > cool question for you, ppl! > > > > > > > > > > > > > > > > > > > > Here's my story. Recently I entered a new company (gambling > > > > > > > > > > games), after working few weeks, after getting accustomed > > > > > > > > > > with a code, I > > > > > > > > > > found that they are building > > > > > > > > > > very-unnecessarly-complex-distibuted-application ... I was > > > > > > > > > > unhappy few days, > > > > > > > > > > because couldn't even imagine how to support ALL THAT CRAP > > > > > > > > > > in an upcoming > > > > > > > > > > future. So I suggested ZMQ hoping that ZMQ will "open eyes" > > > > > > > > > > to others. But, > > > > > > > > > > as a feedback I got one big fundamental concern (from chief > > > > > > > > > > architects): > > > > > > > > > > > > > > > > > > > > - we have to know only one thing about every message: it > > > > > > > > > > has been > > > > > > > > > > delivered onto remote peer or not > > > > > > > > > > > > > > > > > > > > And few additional comments: > > > > > > > > > > -we don't care if message will get lost on a network > > > > > > > > > > - we don't need guarantee deliveri > > > > > > > > > > - no RPC / everything is asynchronous > > > > > > > > > > - we don't need HWM > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > So I'm here, because I really can't address this question: > > > > > > > > > > "for > > > > > > > > > > every single message how to know : whether it was delivered > > > > > > > > > > or not" . > > > > > > > > > > > > > > > > > > > > Thanks in advance. And appreciate for your help. > > > > > > > > > > _______________________________________________ > > > > > > > > > > zeromq-dev mailing list > > > > > > > > > > [email protected] > > > > > > > > > > (mailto:[email protected]) > > > > > > > > > > (mailto:[email protected]) > > > > > > > > > > http://lists.zeromq.org/mailman/listinfo/zeromq-dev > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > _______________________________________________ > > > > > > > > > zeromq-dev mailing list > > > > > > > > > [email protected] > > > > > > > > > (mailto:[email protected]) > > > > > > > > > (mailto:[email protected]) > > > > > > > > > http://lists.zeromq.org/mailman/listinfo/zeromq-dev > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > _______________________________________________ > > > > > > > > zeromq-dev mailing list > > > > > > > > [email protected] > > > > > > > > (mailto:[email protected]) > > > > > > > > (mailto:[email protected]) > > > > > > > > http://lists.zeromq.org/mailman/listinfo/zeromq-dev > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > _______________________________________________ > > > > > > > zeromq-dev mailing list > > > > > > > [email protected] (mailto:[email protected]) > > > > > > > http://lists.zeromq.org/mailman/listinfo/zeromq-dev > > > > > > > > > > > > > > > > > > > > > > > > _______________________________________________ > > > > > > zeromq-dev mailing list > > > > > > [email protected] (mailto:[email protected]) > > > > > > http://lists.zeromq.org/mailman/listinfo/zeromq-dev > > > > > > > > > > > > > > > > > > _______________________________________________ > > > > > > zeromq-dev mailing list > > > > > > [email protected] (mailto:[email protected]) > > > > > > http://lists.zeromq.org/mailman/listinfo/zeromq-dev > > > > > > > > > > > > > > > > > > > > _______________________________________________ > > > > > zeromq-dev mailing list > > > > > [email protected] (mailto:[email protected]) > > > > > http://lists.zeromq.org/mailman/listinfo/zeromq-dev > > > > > > > > > > > > > > > > _______________________________________________ > > > > zeromq-dev mailing list > > > > [email protected] (mailto:[email protected]) > > > > http://lists.zeromq.org/mailman/listinfo/zeromq-dev > > > > > > _______________________________________________ > > > zeromq-dev mailing list > > > [email protected] (mailto:[email protected]) > > > http://lists.zeromq.org/mailman/listinfo/zeromq-dev > > > > > > _______________________________________________ > > zeromq-dev mailing list > > [email protected] (mailto:[email protected]) > > http://lists.zeromq.org/mailman/listinfo/zeromq-dev > > > > _______________________________________________ > zeromq-dev mailing list > [email protected] > http://lists.zeromq.org/mailman/listinfo/zeromq-dev > > _______________________________________________ > zeromq-dev mailing list > [email protected] > http://lists.zeromq.org/mailman/listinfo/zeromq-dev
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