Provided by: libxs-dev_1.2.0-2build1_amd64 
NAME
xs_setsockopt - set Crossroads socket options
SYNOPSIS
int xs_setsockopt (void *socket, int option_name, const void *option_value, size_t option_len);
Caution: All options, with the exception of XS_SUBSCRIBE, XS_UNSUBSCRIBE and XS_LINGER, only take effect
for subsequent socket bind/connects.
DESCRIPTION
The xs_setsockopt() function shall set the option specified by the option_name argument to the value
pointed to by the option_value argument for the Crossroads socket pointed to by the socket argument. The
option_len argument is the size of the option value in bytes.
The following socket options can be set with the xs_setsockopt() function:
XS_SNDHWM: Set high water mark for outbound messages
The XS_SNDHWM option shall set the high water mark for outbound messages on the specified socket. The
high water mark is a hard limit on the maximum number of outstanding messages the library shall queue in
memory for any single peer that the specified socket is communicating with.
If this limit has been reached the socket shall enter an exceptional state and depending on the socket
type, the library shall take appropriate action such as blocking or dropping sent messages. Refer to the
individual socket descriptions in xs_socket(3) for details on the exact action taken for each socket
type.
Option value type int
Option value unit messages
Default value 1000
Applicable socket types all
XS_RCVHWM: Set high water mark for inbound messages
The XS_RCVHWM option shall set the high water mark for inbound messages on the specified socket. The high
water mark is a hard limit on the maximum number of outstanding messages the libray shall queue in memory
for any single peer that the specified socket is communicating with.
If this limit has been reached the socket shall enter an exceptional state and depending on the socket
type, the library shall take appropriate action such as blocking or dropping sent messages. Refer to the
individual socket descriptions in xs_socket(3) for details on the exact action taken for each socket
type.
Option value type int
Option value unit messages
Default value 1000
Applicable socket types all
XS_AFFINITY: Set I/O thread affinity
The XS_AFFINITY option shall set the I/O thread affinity for newly created connections on the specified
socket.
Affinity determines which threads from the Crossroads I/O thread pool associated with the socket’s
context shall handle newly created connections. A value of zero specifies no affinity, meaning that work
shall be distributed fairly among all Crossroads 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 socket shall be handled exclusively by I/O threads 1 and 2.
See also xs_init(3) for details on allocating the number of I/O threads for a specific context.
Option value type uint64_t
Option value unit N/A (bitmap)
Default value 0
Applicable socket types N/A
XS_SUBSCRIBE: Establish message filter
The XS_SUBSCRIBE option shall establish a new message filter on a XS_SUB socket. Newly created XS_SUB
sockets shall filter out all incoming messages, therefore you should call this option to establish an
initial message filter.
An empty option_value of length zero shall subscribe to all incoming messages. A non-empty option_value
shall subscribe to all messages beginning with the specified prefix. Multiple filters may be attached to
a single XS_SUB socket, in which case a message shall be accepted if it matches at least one filter.
Option value type binary data
Option value unit N/A
Default value N/A
Applicable socket types XS_SUB
XS_UNSUBSCRIBE: Remove message filter
The XS_UNSUBSCRIBE option shall remove an existing message filter on a XS_SUB socket. The filter
specified must match an existing filter previously established with the XS_SUBSCRIBE option. If the
socket has several instances of the same filter attached the XS_UNSUBSCRIBE option shall remove only one
instance, leaving the rest in place and functional.
Option value type binary data
Option value unit N/A
Default value N/A
Applicable socket types XS_SUB
XS_IDENTITY: Set socket identity
The XS_IDENTITY option shall set the identity of the specified socket. Socket identity is used only by
request/reply pattern. Namely, it can be used in tandem with a XS_XREP socket to route messages to the
peer with specific identity.
Identity should be at least one byte and at most 255 bytes long. Identities starting with binary zero are
reserved for use by Crossroads infrastructure.
Option value type binary data
Option value unit N/A
Default value NULL
Applicable socket types all
XS_RATE: Set multicast data rate
The XS_RATE option shall set the maximum send or receive data rate for multicast transports such as
xs_pgm(7) using the specified socket.
Option value type int
Option value unit kilobits per second
Default value 100
Applicable socket types all, when using multicast transports
XS_RECOVERY_IVL: Set multicast recovery interval
The XS_RECOVERY_IVL option shall set the recovery interval for multicast transports using the specified
socket. The recovery interval determines the maximum time in milliseconds that a receiver can be absent
from a multicast group before unrecoverable data loss will occur.
Caution
Exercise care when setting large recovery intervals as the data needed for recovery will be held in
memory. For example, a 1 minute recovery interval at a data rate of 1Gbps requires a 7GB in-memory
buffer.
Option value type int
Option value unit milliseconds
Default value 10000
Applicable socket types all, when using multicast transports
XS_SNDBUF: Set kernel transmit buffer size
The XS_SNDBUF option shall set the underlying kernel transmit buffer size for the socket to the specified
size in bytes. A value of zero means leave the OS default unchanged. For details please refer to your
operating system documentation for the SO_SNDBUF socket option.
Option value type int
Option value unit bytes
Default value 0
Applicable socket types all
XS_RCVBUF: Set kernel receive buffer size
The XS_RCVBUF option shall set the underlying kernel receive buffer size for the socket to the specified
size in bytes. A value of zero means leave the OS default unchanged. For details refer to your operating
system documentation for the SO_RCVBUF socket option.
Option value type int
Option value unit bytes
Default value 0
Applicable socket types all
XS_LINGER: Set linger period for socket shutdown
The XS_LINGER option shall set the linger period for the specified socket. 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 xs_close(3), and further affects the termination of the socket’s context with xs_term(3). The
following outlines the different behaviours:
• The default value of -1 specifies an infinite linger period. Pending messages shall not be discarded
after a call to xs_close(); attempting to terminate the socket’s context with xs_term() shall block
until all pending messages have been sent to a peer.
• The value of 0 specifies no linger period. Pending messages shall be discarded immediately when the
socket is closed with xs_close().
• Positive values specify an upper bound for the linger period in milliseconds. Pending messages shall
not be discarded after a call to xs_close(); attempting to terminate the socket’s context with
xs_term() 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.
Option value type int
Option value unit milliseconds
Default value -1 (infinite)
Applicable socket types all
XS_RECONNECT_IVL: Set reconnection interval
The XS_RECONNECT_IVL option shall set the initial reconnection interval for the specified socket. The
reconnection interval is the period the library shall wait between attempts to reconnect disconnected
peers when using connection-oriented transports.
Note
The reconnection interval may be randomized by the library to prevent reconnection storms in
topologies with a large number of peers per socket.
Option value type int
Option value unit milliseconds
Default value 100
Applicable socket types all, only for connection-oriented
transports
XS_RECONNECT_IVL_MAX: Set maximum reconnection interval
The XS_RECONNECT_IVL_MAX option shall set the maximum reconnection interval for the specified socket.
This is the maximum period the library shall wait between attempts to reconnect. On each reconnect
attempt, the previous interval shall be doubled untill XS_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 XS_RECONNECT_IVL.
Note
Values less than XS_RECONNECT_IVL will be ignored.
Option value type int
Option value unit milliseconds
Default value 0 (only use XS_RECONNECT_IVL)
Applicable socket types all, only for connection-oriented
transports
XS_BACKLOG: Set maximum length of the queue of outstanding connections
The XS_BACKLOG option shall set the maximum length of the queue of outstanding peer connections for the
specified socket; this only applies to connection-oriented transports. For details refer to your
operating system documentation for the listen function.
Option value type int
Option value unit connections
Default value 100
Applicable socket types all, only for connection-oriented
transports.
XS_MAXMSGSIZE: Maximum acceptable inbound message size
Limits the size of the inbound message. If a peer sends a message larger than XS_MAXMSGSIZE it is
disconnected.
Option value type uint64_t
Option value unit bytes
Default value 2^64-1
Applicable socket types all
XS_MULTICAST_HOPS: Maximum network hops for multicast packets
Sets the time-to-live field in every multicast packet sent from this socket. The default is 1 which means
that the multicast packets don’t leave the local network.
Option value type int
Option value unit network hops
Default value 1
Applicable socket types all, when using multicast transports
XS_RCVTIMEO: Maximum time before a recv operation returns with EAGAIN
Sets the timeout for receive operation on the socket. If the value is 0, xs_recv(3) 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.
Option value type int
Option value unit milliseconds
Default value -1 (infinite)
Applicable socket types all
XS_SNDTIMEO: Maximum time before a send operation returns with EAGAIN
Sets the timeout for send operation on the socket. If the value is 0, xs_send(3) 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.
Option value type int
Option value unit milliseconds
Default value -1 (infinite)
Applicable socket types all
XS_IPV4ONLY: Use IPv4-only sockets
Sets the underlying native socket type. A value of 1 will use IPv4 sockets, while the value of 0 will use
IPv6 sockets. An IPv6 socket lets applications connect to and accept connections from both IPv4 and IPv6
hosts.
Option value type int
Option value unit boolean
Default value 1 (true)
Applicable socket types all, when using TCP transport.
XS_KEEPALIVE: Enable transport keepalives
When set to 1, this option enables use of protocol keepalives on the socket, if supported by the
underlying transport protocol.
Option value type int
Option value unit boolean
Default value 0 (false)
Applicable socket types all, when using TCP transport.
XS_SURVEY_TIMEOUT: Sets the deadline for the survey
Specifies how long to wait for responses to the survey. After the interval expires, any firther calls to
xs_recv() will return EAGAIN error. All the responses received later on will be silently discarded. Value
of -1 means infinite.
Option value type int
Option value unit milliseconds
Default value -1 (infinite)
Applicable socket types XS_SURVEYOR
RETURN VALUE
The xs_setsockopt() function shall return zero if successful. Otherwise it shall return -1 and set errno
to one of the values defined below.
ERRORS
EINVAL
The requested option option_name is unknown, or the requested option_len or option_value is invalid.
ETERM
The context associated with the specified socket was terminated.
ENOTSOCK
The provided socket was invalid.
EINTR
The operation was interrupted by delivery of a signal.
EXAMPLE
Subscribing to messages on a XS_SUB socket.
/* Subscribe to all messages */
rc = xs_setsockopt (socket, XS_SUBSCRIBE, "", 0);
assert (rc == 0);
/* Subscribe to messages prefixed with "ANIMALS.CATS" */
rc = xs_setsockopt (socket, XS_SUBSCRIBE, "ANIMALS.CATS", 12);
Setting I/O thread affinity.
int64_t affinity;
/* Incoming connections on TCP port 5555 shall be handled by I/O thread 1 */
affinity = 1;
rc = xs_setsockopt (socket, XS_AFFINITY, &affinity, sizeof affinity);
assert (rc == 0);
rc = xs_bind (socket, "tcp://lo:5555");
assert (rc != -1);
/* Incoming connections on TCP port 5556 shall be handled by I/O thread 2 */
affinity = 2;
rc = xs_setsockopt (socket, XS_AFFINITY, &affinity, sizeof affinity);
assert (rc == 0);
rc = xs_bind (socket, "tcp://lo:5556");
assert (rc != -1);
SEE ALSO
xs_getsockopt(3) xs_socket(3) xs(7)
AUTHORS
The Crossroads documentation was written by Martin Sustrik <sustrik@250bpm.com[1]> and Martin Lucina
<martin@lucina.net[2]>.
NOTES
1. sustrik@250bpm.com
mailto:sustrik@250bpm.com
2. martin@lucina.net
mailto:martin@lucina.net
Crossroads I/O 1.2.0 06/13/2012 XS_SETSOCKOPT(3)