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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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);

AUTHORS

The Crossroads documentation was written by Martin Sustrik <m[blue][email protected]m[][1]> and Martin Lucina <m[blue][email protected]m[][2]>.

NOTES

1.

[email protected]

mailto:[email protected]

2.

[email protected]

mailto:[email protected]