'\" t
.\"     Title: zmq_getsockopt
.\"    Author: [see the "AUTHORS" section]
.\" Generator: DocBook XSL Stylesheets v1.75.2 <http://docbook.sf.net/>
.\"      Date: 04/04/2012
.\"    Manual: 0MQ Manual
.\"    Source: 0MQ 2.2.0
.\"  Language: English
.\"
.TH "ZMQ_GETSOCKOPT" "3" "04/04/2012" "0MQ 2\&.2\&.0" "0MQ Manual"
.\" -----------------------------------------------------------------
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.\" http://bugs.debian.org/507673
.\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html
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.el       .ds Aq '
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.nh
.\" disable justification (adjust text to left margin only)
.ad l
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.\" * MAIN CONTENT STARTS HERE *
.\" -----------------------------------------------------------------
.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_TYPE: Retrieve socket type"
.sp
The \fIZMQ_TYPE\fR option shall retrieve the socket type for the specified \fIsocket\fR\&. The socket type is specified at socket creation time and cannot be modified afterwards\&.
.TS
tab(:);
lt lt
lt lt
lt lt
lt lt.
T{
.sp
Option value type
T}:T{
.sp
int
T}
T{
.sp
Option value unit
T}:T{
.sp
N/A
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_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_RCVTIMEO: Maximum time before a socket operation returns with EAGAIN"
.sp
Retrieve the timeout for recv operation on the socket\&. If the value is 0, \fIzmq_recv(3)\fR will return immediately, with a EAGAIN error if there is no message to receive\&. If the value is \-1, it will block until a message is available\&. For all other values, it will wait for a message for that amount of time before returning with an EAGAIN error\&.
.TS
tab(:);
lt lt
lt lt
lt lt
lt lt.
T{
.sp
Option value type
T}:T{
.sp
int
T}
T{
.sp
Option value unit
T}:T{
.sp
milliseconds
T}
T{
.sp
Default value
T}:T{
.sp
\-1 (infinite)
T}
T{
.sp
Applicable socket types
T}:T{
.sp
all
T}
.TE
.sp 1
.SS "ZMQ_SNDTIMEO: Maximum time before a socket operation returns with EAGAIN"
.sp
Retrieve the timeout for send operation on the socket\&. If the value is 0, \fIzmq_send(3)\fR will return immediately, with a EAGAIN error if the message cannot be sent\&. If the value is \-1, it will block until the message is sent\&. For all other values, it will try to send the message for that amount of time before returning with an EAGAIN error\&.
.TS
tab(:);
lt lt
lt lt
lt lt
lt lt.
T{
.sp
Option value type
T}:T{
.sp
int
T}
T{
.sp
Option value unit
T}:T{
.sp
milliseconds
T}
T{
.sp
Default value
T}:T{
.sp
\-1 (infinite)
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 its 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 infrastructure (\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_RECOVERY_IVL_MSEC: Get multicast recovery interval in milliseconds"
.sp
The \fIZMQ_RECOVERY_IVL\(cq_MSEC option shall retrieve the recovery interval, in milliseconds, for multicast transports using the specified \*(Aqsocket\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\&.
.sp
For backward compatibility, the default value of \fIZMQ_RECOVERY_IVL_MSEC\fR is \-1 indicating that the recovery interval should be obtained from the \fIZMQ_RECOVERY_IVL\fR option\&. However, if the \fIZMQ_RECOVERY_IVL_MSEC\fR value is not zero, then it will take precedence, and be used\&.
.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
milliseconds
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_MCAST_LOOP: Control multicast loop\-back"
.sp
The \fIZMQ_MCAST_LOOP\fR option controls whether data sent via multicast transports can also be received by the sending host via loop\-back\&. A value of zero indicates that the loop\-back functionality is disabled, while the default value of 1 indicates that the loop\-back functionality is enabled\&. Leaving multicast loop\-back 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
.SS "ZMQ_LINGER: Retrieve linger period for socket shutdown"
.sp
The \fIZMQ_LINGER\fR option shall retrieve the linger period for the specified \fIsocket\fR\&. The linger period determines how long pending messages which have yet to be sent to a peer shall linger in memory after a socket is closed with \fBzmq_close\fR(3), and further affects the termination of the socket\(cqs context with \fBzmq_term\fR(3)\&. The following outlines the different behaviours:
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
The default value of
\fI\-1\fR
specifies an infinite linger period\&. Pending messages shall not be discarded after a call to
\fIzmq_close()\fR; attempting to terminate the socket\(cqs context with
\fIzmq_term()\fR
shall block until all pending messages have been sent to a peer\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
The value of
\fI0\fR
specifies no linger period\&. Pending messages shall be discarded immediately when the socket is closed with
\fIzmq_close()\fR\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Positive values specify an upper bound for the linger period in milliseconds\&. Pending messages shall not be discarded after a call to
\fIzmq_close()\fR; attempting to terminate the socket\(cqs context with
\fIzmq_term()\fR
shall block until either all pending messages have been sent to a peer, or the linger period expires, after which any pending messages shall be discarded\&.
.TS
tab(:);
lt lt
lt lt
lt lt
lt lt.
T{
Option value type
T}:T{
int
T}
T{
Option value unit
T}:T{
milliseconds
T}
T{
Default value
T}:T{
\-1 (infinite)
T}
T{
Applicable socket types
T}:T{
all
T}
.TE
.sp 1
.RE
.SS "ZMQ_RECONNECT_IVL: Retrieve reconnection interval"
.sp
The \fIZMQ_RECONNECT_IVL\fR option shall retrieve the initial reconnection interval for the specified \fIsocket\fR\&. The reconnection interval is the period 0MQ shall wait between attempts to reconnect disconnected peers when using connection\-oriented transports\&.
.if n \{\
.sp
.\}
.RS 4
.it 1 an-trap
.nr an-no-space-flag 1
.nr an-break-flag 1
.br
.ps +1
\fBNote\fR
.ps -1
.br
.sp
The reconnection interval may be randomized by 0MQ to prevent reconnection storms in topologies with a large number of peers per socket\&.
.sp .5v
.RE
.TS
tab(:);
lt lt
lt lt
lt lt
lt lt.
T{
.sp
Option value type
T}:T{
.sp
int
T}
T{
.sp
Option value unit
T}:T{
.sp
milliseconds
T}
T{
.sp
Default value
T}:T{
.sp
100
T}
T{
.sp
Applicable socket types
T}:T{
.sp
all, only for connection\-oriented transports
T}
.TE
.sp 1
.SS "ZMQ_RECONNECT_IVL_MAX: Retrieve maximum reconnection interval"
.sp
The \fIZMQ_RECONNECT_IVL_MAX\fR option shall retrieve the maximum reconnection interval for the specified \fIsocket\fR\&. This is the maximum period 0MQ shall wait between attempts to reconnect\&. On each reconnect attempt, the previous interval shall be doubled untill ZMQ_RECONNECT_IVL_MAX is reached\&. This allows for exponential backoff strategy\&. Default value means no exponential backoff is performed and reconnect interval calculations are only based on ZMQ_RECONNECT_IVL\&.
.if n \{\
.sp
.\}
.RS 4
.it 1 an-trap
.nr an-no-space-flag 1
.nr an-break-flag 1
.br
.ps +1
\fBNote\fR
.ps -1
.br
.sp
Values less than ZMQ_RECONNECT_IVL will be ignored\&.
.sp .5v
.RE
.TS
tab(:);
lt lt
lt lt
lt lt
lt lt.
T{
.sp
Option value type
T}:T{
.sp
int
T}
T{
.sp
Option value unit
T}:T{
.sp
milliseconds
T}
T{
.sp
Default value
T}:T{
.sp
0 (only use ZMQ_RECONNECT_IVL)
T}
T{
.sp
Applicable socket types
T}:T{
.sp
all, only for connection\-oriented transport
T}
.TE
.sp 1
.SS "ZMQ_BACKLOG: Retrieve maximum length of the queue of outstanding connections"
.sp
The \fIZMQ_BACKLOG\fR option shall retrieve the maximum length of the queue of outstanding peer connections for the specified \fIsocket\fR; this only applies to connection\-oriented transports\&. For details refer to your operating system documentation for the \fIlisten\fR function\&.
.TS
tab(:);
lt lt
lt lt
lt lt
lt lt.
T{
.sp
Option value type
T}:T{
.sp
int
T}
T{
.sp
Option value unit
T}:T{
.sp
connections
T}
T{
.sp
Default value
T}:T{
.sp
100
T}
T{
.sp
Applicable socket types
T}:T{
.sp
all, only for connection\-oriented transports
T}
.TE
.sp 1
.SS "ZMQ_FD: Retrieve file descriptor associated with the socket"
.sp
The \fIZMQ_FD\fR option shall retrieve the file descriptor associated with the specified \fIsocket\fR\&. The returned file descriptor can be used to integrate the socket into an existing event loop; the 0MQ library shall signal any pending events on the socket in an \fIedge\-triggered\fR fashion by making the file descriptor become ready for reading\&.
.if n \{\
.sp
.\}
.RS 4
.it 1 an-trap
.nr an-no-space-flag 1
.nr an-break-flag 1
.br
.ps +1
\fBNote\fR
.ps -1
.br
.sp
The ability to read from the returned file descriptor does not necessarily indicate that messages are available to be read from, or can be written to, the underlying socket; applications must retrieve the actual event state with a subsequent retrieval of the \fIZMQ_EVENTS\fR option\&.
.sp .5v
.RE
.if n \{\
.sp
.\}
.RS 4
.it 1 an-trap
.nr an-no-space-flag 1
.nr an-break-flag 1
.br
.ps +1
\fBCaution\fR
.ps -1
.br
.sp
The returned file descriptor is intended for use with a \fIpoll\fR or similar system call only\&. Applications must never attempt to read or write data to it directly, neither should they try to close it\&.
.sp .5v
.RE
.TS
tab(:);
lt lt
lt lt
lt lt
lt lt.
T{
.sp
Option value type
T}:T{
.sp
int on POSIX systems, SOCKET on Windows
T}
T{
.sp
Option value unit
T}:T{
.sp
N/A
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_EVENTS: Retrieve socket event state"
.sp
The \fIZMQ_EVENTS\fR option shall retrieve the event state for the specified \fIsocket\fR\&. The returned value is a bit mask constructed by OR\(cqing a combination of the following event flags:
.PP
\fBZMQ_POLLIN\fR
.RS 4
Indicates that at least one message may be received from the specified socket without blocking\&.
.RE
.PP
\fBZMQ_POLLOUT\fR
.RS 4
Indicates that at least one message may be sent to the specified socket without blocking\&.
.RE
.sp
The combination of a file descriptor returned by the \fIZMQ_FD\fR option being ready for reading but no actual events returned by a subsequent retrieval of the \fIZMQ_EVENTS\fR option is valid; applications should simply ignore this case and restart their polling operation/event loop\&.
.TS
tab(:);
lt lt
lt lt
lt lt
lt lt.
T{
.sp
Option value type
T}:T{
.sp
uint32_t
T}
T{
.sp
Option value unit
T}:T{
.sp
N/A (flags)
T}
T{
.sp
Default value
T}:T{
.sp
N/A
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
\fBENOTSOCK\fR
.RS 4
The provided
\fIsocket\fR
was invalid\&.
.RE
.PP
\fBEINTR\fR
.RS 4
The operation was interrupted by delivery of a signal\&.
.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
This manual page was written by the 0MQ community\&.