| [Time] Name | Message |
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[03:37] alisdair
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is zeromq a protocol at all, or is it mostly an alternate interface to sockets?
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[06:07] travlr
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alisdair: zmq transports a "blob" of data so the descriptor of the blob is provided by the app programmer.
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[06:08] alisdair
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travlr: i get that, but does it wrap that at all? can i use zeromq at only one end of a connection, or does it need to be used at both?
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[06:09] travlr
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alisdair: "only one end" ... do you mean using standard-sockets in the system... if so see zmq_poll() doc
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[06:09] alisdair
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well
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[06:09] alisdair
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if i write a client using zeromq
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[06:09] alisdair
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does the server need to be aware of that?
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[06:10] travlr
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is the server using a standard-socket?
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[06:10] travlr
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bsd socket?
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[06:11] travlr
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look at the zmq_poll() doc I think that will help answer your question.
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[06:13] alisdair
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standard sockets
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[06:13] travlr
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also, see the mato's zmq-camera example of integrating other system aspects: http://github.com/mato/zeromq-examples
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[06:14] alisdair
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i just want to know, does zeromq add any wrapping to a packet? if i send a packet from a client written using zeromq, does the receiving system need to know anything about it to process it? is it just a regular udp/tcp packet?
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[06:16] travlr
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zmq_recv() just recieves the "blob". no un-wrapping is necessary. it does wrap the blob with possible addressing and delineation protocol aspects.
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[06:17] travlr
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see: zmq_tcp(7), zmq_pgm(7), zmq_ipc(7), and zmq_inproc(7) for details.
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[06:17] travlr
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http://api.zeromq.org/zmq.html
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[06:33] Umesh
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http://www.zeromq.org/whitepapers:design-v06#toc0
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[06:33] Umesh
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is this white paper outdated ?
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[06:36] travlr
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Umesh: In a sense yes, but not totally. zmq2 is a departure from zmq1 in that is entirely brokerless and there is no message protocol. I don't know yet myself where all the similarities and differences lie.
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[06:39] sustrik
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Umesh: in general, yes. what exactly are you interested in?
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[06:41] Umesh
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I am intrested in load balancing for client server
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[06:41] Umesh
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there it was how we can do load balancing in the zmq is described in that white paper
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[06:42] Umesh
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while reading that paper i felt it is outdated ...
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[06:42] Umesh
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so we can't do load balancing inbuilt in the zmq ... right ?
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[06:42] Umesh
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for REQ/REP socket
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[06:45] sustrik
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yes, there's load balancing in-built
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[06:45] sustrik
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when there are several peers to REQ socket
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[06:45] sustrik
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the requests are load-balanced among them
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[06:45] Umesh
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ok
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[06:46] Umesh
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then how we can choose the endpoint for that peer ...
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[06:46] sustrik
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?
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[06:46] Umesh
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I haven't seen any such apis
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[06:46] sustrik
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there's no need for specific apis
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[06:46] Umesh
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means say i have a name server on m1, m2 and m3 ...
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[06:47] sustrik
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s =socket (REQ);
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[06:47] sustrik
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s.connect (m1);
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[06:47] sustrik
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s.connect (m2);
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[06:47] sustrik
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s.connect (m3);
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[06:47] sustrik
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that's what you meant?
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[06:47] Umesh
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then I create a REQ socket and then connect ...
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[06:48] Umesh
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then send data ...
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[06:48] sustrik
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yes
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[06:48] Umesh
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so data will go to machine where i connect ...
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[06:48] Umesh
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right ...
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[06:48] sustrik
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or you can bind and let name servers connect to your app
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[06:48] Umesh
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ok so you mean i should connect to all name server ... right ?
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[06:48] sustrik
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depends on what you are doing
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[06:48] sustrik
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right
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[06:48] Umesh
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to enable laod balancing ...
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[06:49] Umesh
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is there any way to know all machines on the port using the zmq ... something like getaddribfo
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[06:50] Umesh
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just a summary of our discussion : To enable load balansing in the zmq ... REQ socket should connect to all REP sockets it know ... right ?
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[06:50] sustrik
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REQ sockets should have multiple peers
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[06:51] Umesh
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yup ...
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[06:51] sustrik
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whether they are connected to are they connect themselves
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[06:51] sustrik
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as for locating the machines... it's pretty hard when you think of Intetnet
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[06:51] sustrik
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there may be a machine running somewhere in Ougadougou
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[06:52] sustrik
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no, no way to locate all the instances
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[06:52] Umesh
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ok
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[06:52] sustrik
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what you may want is a shared queue
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[06:52] sustrik
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i.e. all clients connect to the shared queue
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[06:52] Umesh
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but for lan ... I can still use the getaddrinfo call ... to find all the machines to connect to ...
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[06:52] sustrik
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all servers connect to the shared queue
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[06:53] sustrik
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the share queue load balances the requests among the servers
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[06:53] Umesh
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means use a queue device in between ... create one hop ..
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[06:53] sustrik
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yes
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[06:53] sustrik
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ad getaddrinfo: i am afraid it doesn't work that way
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[06:53] Umesh
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but for lan ... I can still use the getaddrinfo call ... to find all the machines to connect to ...
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[06:54] sustrik
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how would you do that?
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[06:54] Umesh
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i will just not specify node in that call ... only specify port ... get all the machines listening on that port ...
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[06:55] sustrik
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i doubt getaddrinfo works that way
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[06:55] Umesh
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getaddrinfo(NULL, PORT, &hints, &servinfo))
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[06:55] sustrik
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does it work?
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[06:55] Umesh
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here PORT will be the port of the name server ...
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[06:56] Umesh
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it works for normal tcp ip ...
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[06:56] sustrik
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wow
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[06:56] Umesh
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so i think it will work for zmq ...
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[06:56] Umesh
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isn't it ...
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[06:56] Umesh
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?
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[06:56] sustrik
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if it works then it would surely work
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[06:56] sustrik
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even for 0mq
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[06:57] Umesh
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ok
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[06:57] Umesh
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i will give the try ...
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[06:58] Umesh
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one more doubt ... which load balancing we does ?
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[06:58] Umesh
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means round robin ... etc ?
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[07:15] sustrik
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round robin
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[07:16] Umesh
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ok
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[07:27] Umesh
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hi sustrik ...
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[07:27] Umesh
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i think i was wrong for getaddrinfo ...
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[07:27] Umesh
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it will not work for normal tcp/ip as well
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[07:39] sustrik
|
:)
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[07:55] Efhache
|
Hi everybody
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[07:56] Efhache
|
I come back to you because I need some help... I'm learning how to use zmq... In this goal I test some example application.
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[07:56] Efhache
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Right now I test the tcp client/server application example
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[07:57] Efhache
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but I've a little problem... when I try to send my message I've an "unknown error" (returned by strerror) and the client of course segfault when I try to receive
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[07:58] Efhache
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The error is "ERREUR -1 send: Unknown error 156384763 "
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[07:58] Efhache
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Could you help me ???
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[07:58] Efhache
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here is the line code used to send my message : rc = zmq_send (s, &query, 0);
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[08:03] travlr
|
If you post the code piece somewhere, I'll try to help.
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[08:08] Efhache
|
Can I post it here?
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[08:08] Efhache
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(piece by piece) ?
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[08:09] travlr
|
use dpaste or gist or some similar web service so I may be able to see what might be incorrect
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[08:12] travlr
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http://dpaste.com/ or http://gist.github.com/ or some other
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[08:12] Efhache
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http://dpaste.com/hold/210910/
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[08:14] sustrik
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Efhache: 0mq defines few additional errors
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[08:14] sustrik
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use zmq_strerror instead of strerror to decode them
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[08:14] Efhache
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ok
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[08:17] Efhache
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ERREUR -1 send: Operation cannot be accomplished in current state
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[08:17] Efhache
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no more information for me...
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[08:17] Efhache
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:-/
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[08:21] travlr
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has the server been executed before the client?
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[08:22] Efhache
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yes of course
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[08:22] Efhache
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and the server is running
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[08:22] sustrik
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REQ/REP sockets reuquire alternate sequence of sends & recvs
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[08:22] sustrik
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so with REQ send a request, the receveive a reply
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[08:23] sustrik
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with REP receiver a request, then send the reply
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[08:23] sustrik
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if you fail to do so you'll get the above error
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[08:24] travlr
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yeah i see it now too. you need to use ZMQ_REQ in your client.
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[08:24] Efhache
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ok
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[08:26] Efhache
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I replace REP by REQ... now I've not error on the send() function. But a segfault on the recv. I must rechange the context before received???
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[08:26] travlr
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no but did you use ZMQ_REP in the server?
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[08:27] Efhache
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Yes
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[08:28] Efhache
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This code comes from the cookbook examples
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[08:28] travlr
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yeah, it should work out of the box. do you want to post the server code to dpaste
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[08:29] Efhache
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ok
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[08:29] Efhache
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http://dpaste.com/hold/210915/
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[08:30] Efhache
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May be I'll study the code from the latency example
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[08:32] travlr
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i don't know because it looks ok, but i may be over looking something
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[08:33] Efhache
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It's ok now
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[08:33] travlr
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what was it?
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[08:33] Efhache
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I've foget the zmq_msg_init of my resultset variable
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[08:34] travlr
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yes i see.. ok cool
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[08:34] Efhache
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thank's a lot for your help ;-)
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[08:35] travlr
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sure
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[08:35] Efhache
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Just to be sure... with this example, I've just a P2P connection between processes ?
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[08:35] Efhache
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If I'd like to make a communication between a process and two (or more) others
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[08:36] Efhache
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I need to create each time a endpoint ?
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[08:36] travlr
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REQ/REP you can use multiple peers.
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[08:37] Efhache
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ok
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[08:37] travlr
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just use connect to the socket multiple times for each client.. etc.
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[08:37] travlr
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then it will load-balance in a round robin fashion.. i don't know if that's what you want
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[08:38] travlr
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you may want PUB/SUB maybe..
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[08:38] travlr
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or other
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[08:43] Efhache
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I've make a rapid test with two client and it seems that it works... but I'd be sure... how can I make in the server to have a specific message for each client
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[08:43] Efhache
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I can find in the server an id of the sender ?
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[08:44] travlr
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i don't think so. try returning a specific message for each client.
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[08:44] travlr
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for testing
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[08:45] Efhache
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ok
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[08:48] Efhache
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thank you for your help
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[08:48] travlr
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k
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[08:53] Efhache
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no chance... the server do not make automatically a difference between the senders... clients received all replies...
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[09:00] travlr
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Efhache: From the zmq_socket doc: "Each request sent is load-balanced among all services, and each reply received is matched with the last issued request."
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[09:52] sustrik
|
Efhache: what do you want to do?
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[09:52] sustrik
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if you want to reply to the requester use REQ/REP
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[09:52] sustrik
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if you want to send to all client use PUB/SUB
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[11:00] bavluo
|
While compiling/install the PyZMQ extension I am getting "zmq/_zmq.c: In function âinit_zmqâ: âEMTHREADâ undeclared (first use in this function)". I have cloned the latest ZMQ and PyZMQ for github
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[12:02] Umesh
|
Is there a way to write distributed REP server in zeromq ...
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[12:12] sustrik
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yes, place a queue device in the middle
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[12:26] Umesh
|
ok
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[12:27] Umesh
|
but it will send a request to all the servers ... write ?
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[12:27] Umesh
|
right ?
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[12:28] Umesh
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or it will load balance the traffic ?
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[12:29] sustrik
|
load balance
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[12:29] sustrik
|
REQ/REP always load balances
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[12:30] sustrik
|
PUB/SUB always distributes the messages to everyone
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[12:31] Umesh
|
just one question : I don't see any lb object in req.hpp
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[12:31] Umesh
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its there in xreq.hpp
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[12:31] Umesh
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so it is like xreq only have laod balancing ...
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[12:34] Efhache
|
travlr : I see only now your response... sorry... what happens if multi client send request, each of the clients received all the replies? right?
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[12:35] Efhache
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sustrik : I'just want to make a lighted broker : when it received a message from one process it re-sent this message to all connected processes.
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[12:36] sustrik
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Umesh: it's there but it's written by hand
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[12:36] sustrik
|
the code should be polished a bit so that REQ uses lb_t as well...
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[12:37] sustrik
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Efhache: such a thing already exists
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[12:37] sustrik
|
use zmq_forwarder to do this
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[12:38] sustrik
|
have a look at an example here: http://github.com/zeromq/zeromq-chat/blob/master/README
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[12:38] Efhache
|
but the example code that I've used seems to do it...
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[12:38] sustrik
|
sure, if you want to implement it yourself, why not
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[12:40] Efhache
|
witouht implemented it myself... the code from 2 hours ago seems do it... I've tested the "server" with two clients and the both have received the reply from servers
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[12:40] Efhache
|
may be a "bug" of my code or is it normal?
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[12:40] sustrik
|
what code? sorry, i missed it
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[12:41] Umesh
|
sustrik : code present in the devices/zmq_queue/zmq_queue.cpp ... can be straight away used as a queue in the middle right ?
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[12:41] sustrik
|
Umesh: yes
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[12:41] Umesh
|
ok
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[12:41] sustrik
|
there's an executable generated for convenience sake: devices/zmq_queue
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[12:42] Umesh
|
but it uses XREQ/XREP sockets .... and my client server uses REQ/REP ...
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[12:42] Umesh
|
then will it work with them ?
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[12:42] sustrik
|
yes
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[12:42] Umesh
|
ok
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[12:54] Efhache
|
sustrik : it was a problem in my code... with a remanence in a string used for reply...
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[12:54] Efhache
|
sustrik : have you an exemple of "broadcasting" ?
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[12:56] sustrik
|
what about this one: http://github.com/zeromq/zeromq-chat
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[12:56] sustrik
|
or this one: http://lwn.net/Articles/370307/ (Java vs. Python)
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[12:57] sustrik
|
or this one: http://nichol.as/zeromq-an-introduction (Python)
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[13:11] Efhache
|
sustrik : thank you... if I goof understand to make a sort of lighted broker. I will must creating two context. One for receiving and one tu publish (server part) and for the clients one for sending and one for subscribing
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[13:11] Efhache
|
is it right?
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[13:12] sustrik
|
what are you trying to do, i still don't get it
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[13:12] sustrik
|
can you describe the scenario?
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[13:14] Efhache
|
OK... one process who received messagre from two (or more) other process and re-sent the receive message to all connected processes
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[13:36] Efhache
|
in C language
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[13:54] sustrik
|
what you need is a single context
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[13:54] sustrik
|
one sub socket
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[13:54] sustrik
|
and one pub
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[13:54] sustrik
|
socket
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[13:55] sustrik
|
get messages from sub socket
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[13:55] sustrik
|
and send them to the pub socket
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[13:55] sustrik
|
that's exactly what zmq_forwarder does
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[14:01] Efhache
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ok
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[14:02] Efhache
|
sorry but it's a new concept for me...
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[14:03] Efhache
|
have you an example in C ?
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[14:05] Efhache
|
I can not find information about zmq_forwarder in the doc (man page) just "comming soon"
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[14:10] Efhache
|
But if I read the chat example (http://github.com/zeromq/zeromq-chat/blob/master/prompt.cpp) message do not come from the client... is it true? And the client can only receive from prompt...
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[14:10] sustrik
|
http://github.com/zeromq/zeromq-chat
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[14:11] Efhache
|
so I need to context no? one for sending message (from a client to prompt) and an other for SUB
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[14:11] sustrik
|
you can merge display and prompt into a single application if you want
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[14:11] Efhache
|
no ?
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[14:11] sustrik
|
nope you can open both sockets from the same context
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[14:12] sustrik
|
forget about multiple context, you're never going to need it
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[14:12] sustrik
|
unless you are doing very advanced stuff
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[14:13] Efhache
|
I think so I do not understand the concept of "context"... I'll read more documentation... sorry
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[14:14] sustrik
|
context is a global state of the library
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[14:14] sustrik
|
you need only one context
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[14:15] Efhache
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ok
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[14:16] Efhache
|
absolute not link with a protocol or a specific socket
|
