'\" t
.\"     Title: zmq_getsockopt
.\"    Author: [see the "AUTHORS" section]
.\" Generator: DocBook XSL Stylesheets v1.75.2 <http://docbook.sf.net/>
.\"      Date: 09/06/2010
.\"    Manual: 0MQ Manual
.\"    Source: 0MQ 2.0.9
.\"  Language: English
.\"
.TH "ZMQ_GETSOCKOPT" "3" "09/06/2010" "0MQ 2\&.0\&.9" "0MQ Manual"
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.SH "NAME"
zmq_getsockopt \- get 0MQ socket options
.SH "SYNOPSIS"
.sp
\fBint zmq_getsockopt (void \fR\fB\fI*socket\fR\fR\fB, int \fR\fB\fIoption_name\fR\fR\fB, void \fR\fB\fI*option_value\fR\fR\fB, size_t \fR\fB\fI*option_len\fR\fR\fB);\fR
.SH "DESCRIPTION"
.sp
The \fIzmq_getsockopt()\fR function shall retrieve the value for the option specified by the \fIoption_name\fR argument for the 0MQ socket pointed to by the \fIsocket\fR argument, and store it in the buffer pointed to by the \fIoption_value\fR argument\&. The \fIoption_len\fR argument is the size in bytes of the buffer pointed to by \fIoption_value\fR; upon successful completion \fIzmq_getsockopt()\fR shall modify the \fIoption_len\fR argument to indicate the actual size of the option value stored in the buffer\&.
.sp
The following options can be retrieved with the \fIzmq_getsockopt()\fR function:
.SS "ZMQ_RCVMORE: More message parts to follow"
.sp
The \fIZMQ_RCVMORE\fR option shall return a boolean value indicating if the multi\-part message currently being read from the specified \fIsocket\fR has more message parts to follow\&. If there are no message parts to follow or if the message currently being read is not a multi\-part message a value of zero shall be returned\&. Otherwise, a value of 1 shall be returned\&.
.sp
Refer to \fBzmq_send\fR(3) and \fBzmq_recv\fR(3) for a detailed description of sending/receiving multi\-part messages\&.
.TS
tab(:);
lt lt
lt lt
lt lt
lt lt.
T{
.sp
Option value type
T}:T{
.sp
int64_t
T}
T{
.sp
Option value unit
T}:T{
.sp
boolean
T}
T{
.sp
Default value
T}:T{
.sp
N/A
T}
T{
.sp
Applicable socket types
T}:T{
.sp
all
T}
.TE
.sp 1
.SS "ZMQ_HWM: Retrieve high water mark"
.sp
The \fIZMQ_HWM\fR option shall retrieve the high water mark for the specified \fIsocket\fR\&. The high water mark is a hard limit on the maximum number of outstanding messages 0MQ shall queue in memory for any single peer that the specified \fIsocket\fR is communicating with\&.
.sp
If this limit has been reached the socket shall enter an exceptional state and depending on the socket type, 0MQ shall take appropriate action such as blocking or dropping sent messages\&. Refer to the individual socket descriptions in \fBzmq_socket\fR(3) for details on the exact action taken for each socket type\&.
.sp
The default \fIZMQ_HWM\fR value of zero means "no limit"\&.
.TS
tab(:);
lt lt
lt lt
lt lt
lt lt.
T{
.sp
Option value type
T}:T{
.sp
uint64_t
T}
T{
.sp
Option value unit
T}:T{
.sp
messages
T}
T{
.sp
Default value
T}:T{
.sp
0
T}
T{
.sp
Applicable socket types
T}:T{
.sp
all
T}
.TE
.sp 1
.SS "ZMQ_SWAP: Retrieve disk offload size"
.sp
The \fIZMQ_SWAP\fR option shall retrieve the disk offload (swap) size for the specified \fIsocket\fR\&. A socket which has \fIZMQ_SWAP\fR set to a non\-zero value may exceed it\(cqs high water mark; in this case outstanding messages shall be offloaded to storage on disk rather than held in memory\&.
.sp
The value of \fIZMQ_SWAP\fR defines the maximum size of the swap space in bytes\&.
.TS
tab(:);
lt lt
lt lt
lt lt
lt lt.
T{
.sp
Option value type
T}:T{
.sp
int64_t
T}
T{
.sp
Option value unit
T}:T{
.sp
bytes
T}
T{
.sp
Default value
T}:T{
.sp
0
T}
T{
.sp
Applicable socket types
T}:T{
.sp
all
T}
.TE
.sp 1
.SS "ZMQ_AFFINITY: Retrieve I/O thread affinity"
.sp
The \fIZMQ_AFFINITY\fR option shall retrieve the I/O thread affinity for newly created connections on the specified \fIsocket\fR\&.
.sp
Affinity determines which threads from the 0MQ I/O thread pool associated with the socket\(cqs \fIcontext\fR shall handle newly created connections\&. A value of zero specifies no affinity, meaning that work shall be distributed fairly among all 0MQ I/O threads in the thread pool\&. For non\-zero values, the lowest bit corresponds to thread 1, second lowest bit to thread 2 and so on\&. For example, a value of 3 specifies that subsequent connections on \fIsocket\fR shall be handled exclusively by I/O threads 1 and 2\&.
.sp
See also \fBzmq_init\fR(3) for details on allocating the number of I/O threads for a specific \fIcontext\fR\&.
.TS
tab(:);
lt lt
lt lt
lt lt
lt lt.
T{
.sp
Option value type
T}:T{
.sp
uint64_t
T}
T{
.sp
Option value unit
T}:T{
.sp
N/A (bitmap)
T}
T{
.sp
Default value
T}:T{
.sp
0
T}
T{
.sp
Applicable socket types
T}:T{
.sp
N/A
T}
.TE
.sp 1
.SS "ZMQ_IDENTITY: Retrieve socket identity"
.sp
The \fIZMQ_IDENTITY\fR option shall retrieve the identity of the specified \fIsocket\fR\&. Socket identity determines if existing 0MQ infastructure (\fImessage queues\fR, \fIforwarding devices\fR) shall be identified with a specific application and persist across multiple runs of the application\&.
.sp
If the socket has no identity, each run of an application is completely separate from other runs\&. However, with identity set the socket shall re\-use any existing 0MQ infrastructure configured by the previous run(s)\&. Thus the application may receive messages that were sent in the meantime, \fImessage queue\fR limits shall be shared with previous run(s) and so on\&.
.sp
Identity can be at least one byte and at most 255 bytes long\&. Identities starting with binary zero are reserved for use by 0MQ infrastructure\&.
.TS
tab(:);
lt lt
lt lt
lt lt
lt lt.
T{
.sp
Option value type
T}:T{
.sp
binary data
T}
T{
.sp
Option value unit
T}:T{
.sp
N/A
T}
T{
.sp
Default value
T}:T{
.sp
NULL
T}
T{
.sp
Applicable socket types
T}:T{
.sp
all
T}
.TE
.sp 1
.SS "ZMQ_RATE: Retrieve multicast data rate"
.sp
The \fIZMQ_RATE\fR option shall retrieve the maximum send or receive data rate for multicast transports using the specified \fIsocket\fR\&.
.TS
tab(:);
lt lt
lt lt
lt lt
lt lt.
T{
.sp
Option value type
T}:T{
.sp
int64_t
T}
T{
.sp
Option value unit
T}:T{
.sp
kilobits per second
T}
T{
.sp
Default value
T}:T{
.sp
100
T}
T{
.sp
Applicable socket types
T}:T{
.sp
all, when using multicast transports
T}
.TE
.sp 1
.SS "ZMQ_RECOVERY_IVL: Get multicast recovery interval"
.sp
The \fIZMQ_RECOVERY_IVL\fR option shall retrieve the recovery interval for multicast transports using the specified \fIsocket\fR\&. The recovery interval determines the maximum time in seconds that a receiver can be absent from a multicast group before unrecoverable data loss will occur\&.
.TS
tab(:);
lt lt
lt lt
lt lt
lt lt.
T{
.sp
Option value type
T}:T{
.sp
int64_t
T}
T{
.sp
Option value unit
T}:T{
.sp
seconds
T}
T{
.sp
Default value
T}:T{
.sp
10
T}
T{
.sp
Applicable socket types
T}:T{
.sp
all, when using multicast transports
T}
.TE
.sp 1
.SS "ZMQ_MCAST_LOOP: Control multicast loopback"
.sp
The \fIZMQ_MCAST_LOOP\fR option controls whether data sent via multicast transports can also be received by the sending host via loopback\&. A value of zero indicates that the loopback functionality is disabled, while the default value of 1 indicates that the loopback functionality is enabled\&. Leaving multicast loopback enabled when it is not required can have a negative impact on performance\&. Where possible, disable \fIZMQ_MCAST_LOOP\fR in production environments\&.
.TS
tab(:);
lt lt
lt lt
lt lt
lt lt.
T{
.sp
Option value type
T}:T{
.sp
int64_t
T}
T{
.sp
Option value unit
T}:T{
.sp
boolean
T}
T{
.sp
Default value
T}:T{
.sp
1
T}
T{
.sp
Applicable socket types
T}:T{
.sp
all, when using multicast transports
T}
.TE
.sp 1
.SS "ZMQ_SNDBUF: Retrieve kernel transmit buffer size"
.sp
The \fIZMQ_SNDBUF\fR option shall retrieve the underlying kernel transmit buffer size for the specified \fIsocket\fR\&. A value of zero means that the OS default is in effect\&. For details refer to your operating system documentation for the \fISO_SNDBUF\fR socket option\&.
.TS
tab(:);
lt lt
lt lt
lt lt
lt lt.
T{
.sp
Option value type
T}:T{
.sp
uint64_t
T}
T{
.sp
Option value unit
T}:T{
.sp
bytes
T}
T{
.sp
Default value
T}:T{
.sp
0
T}
T{
.sp
Applicable socket types
T}:T{
.sp
all
T}
.TE
.sp 1
.SS "ZMQ_RCVBUF: Retrieve kernel receive buffer size"
.sp
The \fIZMQ_RCVBUF\fR option shall retrieve the underlying kernel receive buffer size for the specified \fIsocket\fR\&. A value of zero means that the OS default is in effect\&. For details refer to your operating system documentation for the \fISO_RCVBUF\fR socket option\&.
.TS
tab(:);
lt lt
lt lt
lt lt
lt lt.
T{
.sp
Option value type
T}:T{
.sp
uint64_t
T}
T{
.sp
Option value unit
T}:T{
.sp
bytes
T}
T{
.sp
Default value
T}:T{
.sp
0
T}
T{
.sp
Applicable socket types
T}:T{
.sp
all
T}
.TE
.sp 1
.SH "RETURN VALUE"
.sp
The \fIzmq_getsockopt()\fR function shall return zero if successful\&. Otherwise it shall return \-1 and set \fIerrno\fR to one of the values defined below\&.
.SH "ERRORS"
.PP
\fBEINVAL\fR
.RS 4
The requested option
\fIoption_name\fR
is unknown, or the requested
\fIoption_len\fR
or
\fIoption_value\fR
is invalid, or the size of the buffer pointed to by
\fIoption_value\fR, as specified by
\fIoption_len\fR, is insufficient for storing the option value\&.
.RE
.PP
\fBETERM\fR
.RS 4
The 0MQ
\fIcontext\fR
associated with the specified
\fIsocket\fR
was terminated\&.
.RE
.PP
\fBEFAULT\fR
.RS 4
The provided
\fIsocket\fR
was not valid (NULL)\&.
.RE
.SH "EXAMPLE"
.PP
\fBRetrieving the high water mark\fR. 
.sp
.if n \{\
.RS 4
.\}
.nf
/* Retrieve high water mark into hwm */
int64_t hwm;
size_t hwm_size = sizeof (hwm);
rc = zmq_getsockopt (socket, ZMQ_HWM, &hwm, &hwm_size);
assert (rc == 0);
.fi
.if n \{\
.RE
.\}
.sp
.SH "SEE ALSO"
.sp
\fBzmq_setsockopt\fR(3) \fBzmq_socket\fR(3) \fBzmq\fR(7)
.SH "AUTHORS"
.sp
The 0MQ documentation was written by Martin Sustrik <\m[blue]\fBsustrik@250bpm\&.com\fR\m[]\&\s-2\u[1]\d\s+2> and Martin Lucina <\m[blue]\fBmato@kotelna\&.sk\fR\m[]\&\s-2\u[2]\d\s+2>\&.
.SH "NOTES"
.IP " 1." 4
sustrik@250bpm.com
.RS 4
\%mailto:sustrik@250bpm.com
.RE
.IP " 2." 4
mato@kotelna.sk
.RS 4
\%mailto:mato@kotelna.sk
.RE