'\" t
.\"     Title: zmq_proxy_steerable
.\"    Author: [see the "AUTHORS" section]
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\"      Date: 01/17/2021
.\"    Manual: 0MQ Manual
.\"    Source: 0MQ 4.3.4
.\"  Language: English
.\"
.TH "ZMQ_PROXY_STEERABLE" "3" "01/17/2021" "0MQ 4\&.3\&.4" "0MQ Manual"
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.SH "NAME"
zmq_proxy_steerable \- built\-in 0MQ proxy with control flow
.SH "SYNOPSIS"
.sp
\fBint zmq_proxy_steerable (const void \fR\fB\fI*frontend\fR\fR\fB, const void \fR\fB\fI*backend\fR\fR\fB, const void \fR\fB\fI*capture\fR\fR\fB, const void \fR\fB\fI*control\fR\fR\fB);\fR
.SH "DESCRIPTION"
.sp
The \fIzmq_proxy_steerable()\fR function starts the built\-in 0MQ proxy in the current application thread, as \fIzmq_proxy()\fR do\&. Please, refer to this function for the general description and usage\&. We describe here only the additional control flow provided by the socket passed as the fourth argument "control"\&.
.sp
If the control socket is not NULL, the proxy supports control flow\&. If \fIPAUSE\fR is received on this socket, the proxy suspends its activities\&. If \fIRESUME\fR is received, it goes on\&. If \fITERMINATE\fR is received, it terminates smoothly\&. If \fISTATISTICS\fR is received, the proxy will reply on the control socket sending a multipart message with 8 frames, each with an unsigned integer 64\-bit wide that provide in the following order: \- number of messages received by the frontend socket \- number of bytes received by the frontend socket \- number of messages sent out the frontend socket \- number of bytes sent out the frontend socket \- number of messages received by the backend socket \- number of bytes received by the backend socket \- number of messages sent out the backend socket \- number of bytes sent out the backend socket
.sp
At start, the proxy runs normally as if zmq_proxy was used\&.
.sp
If the control socket is NULL, the function behave exactly as if \fBzmq_proxy\fR(3) had been called\&.
.sp
Refer to \fBzmq_socket\fR(3) for a description of the available socket types\&. Refer to \fBzmq_proxy\fR(3) for a description of the zmq_proxy\&.
.SH "EXAMPLE USAGE"
.sp
cf zmq_proxy
.SH "RETURN VALUE"
.sp
The \fIzmq_proxy_steerable()\fR function returns 0 if TERMINATE is sent to its control socket\&. Otherwise, it returns \-1 and \fIerrno\fR set to \fBETERM\fR or \fBEINTR\fR (the 0MQ \fIcontext\fR associated with either of the specified sockets was terminated) or \fBEFAULT\fR (the provided \fIfrontend\fR or \fIbackend\fR was invalid)\&.
.SH "EXAMPLE"
.PP
\fBCreating a shared queue proxy\fR. 
.sp
.if n \{\
.RS 4
.\}
.nf
//  Create frontend, backend and control sockets
void *frontend = zmq_socket (context, ZMQ_ROUTER);
assert (frontend);
void *backend = zmq_socket (context, ZMQ_DEALER);
assert (backend);
void *control = zmq_socket (context, ZMQ_SUB);
assert (control);

//  Bind sockets to TCP ports
assert (zmq_bind (frontend, "tcp://*:5555") == 0);
assert (zmq_bind (backend, "tcp://*:5556") == 0);
assert (zmq_connect (control, "tcp://*:5557") == 0);

// Subscribe to the control socket since we have chosen SUB here
assert (zmq_setsockopt (control, ZMQ_SUBSCRIBE, "", 0));

//  Start the queue proxy, which runs until ETERM or "TERMINATE"
//  received on the control socket
zmq_proxy_steerable (frontend, backend, NULL, control);
.fi
.if n \{\
.RE
.\}
.PP
\fBSet up a controller in another node, process or whatever\fR. 
.sp
.if n \{\
.RS 4
.\}
.nf
void *control = zmq_socket (context, ZMQ_PUB);
assert (control);
assert (zmq_bind (control, "tcp://*:5557") == 0);

// pause the proxy
assert (zmq_send (control, "PAUSE", 5, 0) == 0);

// resume the proxy
assert (zmq_send (control, "RESUME", 6, 0) == 0);

// terminate the proxy
assert (zmq_send (control, "TERMINATE", 9, 0) == 0);

// check statistics
assert (zmq_send (control, "STATISTICS", 10, 0) == 0);
zmq_msg_t stats_msg;

while (1) {
    assert (zmq_msg_init (&stats_msg) == 0);
    assert (zmq_recvmsg (control, &stats_msg, 0) == sizeof (uint64_t));
    assert (rc == sizeof (uint64_t));
    printf ("Stat: %lu\en", *(unsigned long int *)zmq_msg_data (&stats_msg));
    if (!zmq_msg_get (&stats_msg, ZMQ_MORE))
        break;
    assert (zmq_msg_close (&stats_msg) == 0);
}
assert (zmq_msg_close (&stats_msg) == 0);
\-\-\-


SEE ALSO
.fi
.if n \{\
.RE
.\}
.sp
\fBzmq_proxy\fR(3) \fBzmq_bind\fR(3) \fBzmq_connect\fR(3) \fBzmq_socket\fR(3) \fBzmq\fR(7)
.SH "AUTHORS"
.sp
This page was written by the 0MQ community\&. To make a change please read the 0MQ Contribution Policy at \m[blue]\fBhttp://www\&.zeromq\&.org/docs:contributing\fR\m[]\&.