That will work, of course....I'm just curious what the resistance is to letting the HWM policy be settable.
On Thu, Jan 16, 2014 at 3:27 PM, Goswin von Brederlow <[email protected]>wrote: > On Thu, Jan 16, 2014 at 02:45:31PM -0500, Lindley French wrote: > > > This is a common issue. If you can?t recover from dropped messages, > > PUB/SUB is not the correct pattern. > > > > In many cases, this is correct. I do not believe inproc is one of those > > cases, however. With inproc, you should have full control of who is > > subscribing and when they come up relative to the publisher. If your > > subscribers aren't running when you expect them to be running, that's a > > bug. If they aren't running fast enough, dropping messages *might* be a > > solution, or it might not. I don't feel that's a decision that can be > made > > in the general case. > > > > Let me put it this way: If I need one-to-many semantics with backpressure > > and filtering, what should I use? PUB is the only one-to-many socket > type. > > I can write my own filtering code, keep a vector of push sockets, etc. > but > > that seems to defeat the point of ZMQ patterns. PUB is exactly what I > want > > in every way *except* the HWM behavior. > > > > > > On Thu, Jan 16, 2014 at 2:11 PM, Charles Remes <[email protected]> > wrote: > > > > > This is a common issue. If you can?t recover from dropped messages, > > > PUB/SUB is not the correct pattern. > > > > > > This of PUB as a radio antenna. It broadcasts regardless of whether or > not > > > anyone is listening. If there are no listeners, every packet gets > dropped. > > > If a listener is slow, then packets will get dropped. If you need > further > > > guarantees about delivery, then you need to build some kind of protocol > > > (ack, nak, ack window, etc) on top of DEALER/ROUTER. > > > > > > Also, as of libzmq 3.3, I believe the default HWM is 1000 (to prevent > > > memory exhaustion in the default configuration). If you want ?infinite? > > > then setsockopt to -1. > > > > > > As for the dropped messages on inproc, you need to be careful to > confirm > > > that a listener (SUB) is actually up, running and *connected* before > you > > > start PUB?ing otherwise the PUB socket will drop messages. > Synchronization > > > for this is discussed in the guide. Alternately, just have your PUB > ?sleep? > > > for a second after the SUB bind/connects and you should be okay. > > > > > > > > > On Jan 16, 2014, at 1:03 PM, Lindley French <[email protected]> > wrote: > > > > > > Well, aside from the router issue I do like the arrangement for easily > > > handling different messages in different places. However, there may be > a > > > fatal flaw at the moment: PUB's desire to drop messages at the HWM. > While > > > making "drop" a default behavior for PUB is fine, I really don't like > that > > > it's the *only* behavior possible. > > > > > > Then again, that may or may not be the issue here. I haven't touched > the > > > HWM, so it should still be 0 which is theoretically infinite. > Nonetheless, > > > a bunch of my messages in a row vanished into the ether somewhere > between > > > PUB and SUB inproc sockets. > > > > > > > > > On Thu, Jan 16, 2014 at 1:02 PM, Lindley French <[email protected] > >wrote: > > > > > >> I tend to stuff in as many different features as I can when I'm first > > >> learning something new, it helps me get a feel for it. > > >> > > >> You should have seen my first major python program..... > > >> > > >> > > >> On Thu, Jan 16, 2014 at 12:46 PM, Charles Remes <[email protected] > >wrote: > > >> > > >>> Create a socket for each worker thread and have your main thread > resend > > >>> the message down the appropriate socket. Sometimes it isn?t a good > idea to > > >>> try and shoe-horn every zeromq socket pattern into your app. :) > > >>> > > >>> On Jan 16, 2014, at 9:54 AM, Lindley French <[email protected]> > wrote: > > >>> > > >>> > A problem I was wrestling with was, how do I deal with a TCP > > >>> connection where messages of different types may arrive, and may > need to be > > >>> dealt with in different threads? The TCP socket can't be touched > directly > > >>> by multiple threads, of course. The obvious solution was to > immediately > > >>> forward messages arriving on the TCP socket to an inproc socket. > > >>> > > > >>> > I then took it one step further: why not make that inproc socket a > PUB > > >>> socket and make the first part of each message be a topic > identifier, so > > >>> that whichever thread knows how to deal with a particular message > can just > > >>> subscribe to it and ignore the rest? > > >>> > > > >>> > That's a great design, right up until I try to do it with the TCP > > >>> socket being a ROUTER. Now, no matter what the first part of the sent > > >>> message is, the identity will end up being the first part on the > receiving > > >>> end. The PUB/SUB won't work without some tweaking. > > >>> > > > >>> > I don't want to just drop the identity; that's useful information. > I > > >>> could swap the first two parts; that will work, but it's unintuitive > and > > >>> could cause confusion down the road. > > >>> > > > >>> > Any other ideas? > > Add a splitter that simply checks the first frame, looks up the right > target socket and sends the remainder on the message onwards. > Then you can use a simple PUSH/PULL pattern. > > MfG > Goswin > _______________________________________________ > zeromq-dev mailing list > [email protected] > http://lists.zeromq.org/mailman/listinfo/zeromq-dev >
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