f# - Why does ZeroMQ's socket.recv call hang in the following code? -

i have encountered problem simple pub-sub example in zeromq. have read plenty of documentation, cannot seem find answer.

i got libzmq , clrzmq nuget. both functions below socket address is:

let sktaddr = "tcp://127.0.0.1:3456" 

here simple publisher, queues message every second.

// publisher - seems work fine let publisher () : unit =     let skt = (new zmq.context()).socket(zmq.sockettype.pub)     skt.setsockopt(zmq.socketopt.linger, 0)     skt.bind sktaddr     skt.sendmore("test_topic", text.encoding.unicode) |> ignore     let rec h1 () : unit =         let nv = datetime.now.touniversaltime().tostring()         printfn "sending value: %s" nv         skt.send(text.encoding.unicode.getbytes nv) |> ignore         threading.thread.sleep 1000         let swt = new threading.spinwait()         swt.spinonce()         if console.keyavailable             match console.readkey().key             | consolekey.q -> ()             | _ -> h1()         else             h1()     h1() 

the following simple subscriber throws no error, hangs @ line indicated below.

// subscriber let subscriber () : unit =     let skt = (new zmq.context()).socket(zmq.sockettype.sub)     skt.connect sktaddr     skt.subscribe("test_topic", text.encoding.unicode)     let rec h1 () : unit =         let odat = skt.recv() // programme hangs here!         let strodat = (new text.unicodeencoding()).getstring odat         if odat <> null             printfn "received: %s" strodat         else             printfn "no data received"         let swt = new system.threading.spinwait()         swt.spinonce()         if console.keyavailable             match console.readkey().key             | consolekey.q -> ()             | _ -> h1()         else             h1()     h1() 

i have read this question, no solution provided. posting new question here.

thanks in advance help.

i believe problem in publisher:

skt.sendmore("test_topic", text.encoding.unicode)

not knowing f#, appears above statement happens outside loop. if subscriber listening on test_topic, messages originating publisher require topic name precede content each message, publisher must each time sends:

skt.sendmore("test_topic", text.encoding.unicode) skt.send("some data here", text.encoding.unicode) 

..try this...

let publisher () : unit =     let skt = (new zmq.context()).socket(zmq.sockettype.pub)     skt.setsockopt(zmq.socketopt.linger, 0)     skt.bind sktaddr      let rec h1 () : unit =         let nv = datetime.now.touniversaltime().tostring()         printfn "sending value: %s" nv         skt.sendmore("test_topic", text.encoding.unicode) |> ignore         skt.send(text.encoding.unicode.getbytes nv) |> ignore         threading.thread.sleep 1000         let swt = new threading.spinwait()         swt.spinonce()         if console.keyavailable             match console.readkey().key             | consolekey.q -> ()             | _ -> h1()         else             h1()     h1() 

..and subscriber has receive twice each message:

// subscriber let subscriber () : unit =     let skt = (new zmq.context()).socket(zmq.sockettype.sub)     skt.connect sktaddr     skt.subscribe("test_topic", text.encoding.unicode)     let rec h1 () : unit =         let topicname = skt.recv()         let odat = skt.recv()         let strodat = (new text.unicodeencoding()).getstring odat         if odat <> null             printfn "received: %s" strodat         else             printfn "no data received"         let swt = new system.threading.spinwait()         swt.spinonce()         if console.keyavailable             match console.readkey().key             | consolekey.q -> ()             | _ -> h1()         else             h1()     h1()