NAME¶
xs_getsockopt - get Crossroads socket option
SYNOPSIS¶
int xs_getsockopt (void *socket, int
option_name, void *option_value,
size_t *option_len);
DESCRIPTION¶
The xs_getsockopt() function shall retrieve the value for the option
specified by the option_name argument for the Crossroads socket pointed
to by the socket argument, and store it in the buffer pointed to by the
option_value argument. The option_len argument is the size in
bytes of the buffer pointed to by option_value; upon successful
completion xs_getsockopt() shall modify the option_len argument
to indicate the actual size of the option value stored in the buffer.
The following options can be retrieved with the
xs_getsockopt() function:
XS_TYPE: Retrieve socket type¶
The XS_TYPE option shall retrieve the socket type for the specified
socket. The socket type is specified at socket creation time and cannot
be modified afterwards.
Option value type |
int |
Option value unit |
N/A |
Default value |
N/A |
Applicable socket types |
all |
XS_RCVMORE: More message data parts to follow¶
The XS_RCVMORE option shall return True (1) if the message part last
received from the socket was a data part with more parts to follow. If
there are no data parts to follow, this option shall return False (0).
Refer to xs_send(3) and xs_recv(3) for a detailed
description of multi-part messages.
Option value type |
int |
Option value unit |
boolean |
Default value |
N/A |
Applicable socket types |
all |
XS_SNDHWM: Retrieves high water mark for outbound messages¶
The XS_SNDHWM option shall return 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: Retrieve high water mark for inbound messages¶
The XS_RCVHWM option shall return 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 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_AFFINITY: Retrieve I/O thread affinity¶
The XS_AFFINITY option shall retrieve 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 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_IDENTITY: Set socket identity¶
The XS_IDENTITY option shall retrieve 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: Retrieve multicast data rate¶
The XS_RATE option shall retrieve the maximum send or receive data rate
for multicast transports 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: Get multicast recovery interval¶
The XS_RECOVERY_IVL option shall retrieve 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.
Option value type |
int |
Option value unit |
milliseconds |
Default value |
10000 |
Applicable socket types |
all, when using multicast transports |
XS_SNDBUF: Retrieve kernel transmit buffer size¶
The XS_SNDBUF option shall retrieve the underlying kernel transmit buffer
size for the specified socket. A value of zero means that the OS
default is in effect. For details 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: Retrieve kernel receive buffer size¶
The XS_RCVBUF option shall retrieve the underlying kernel receive buffer
size for the specified socket. A value of zero means that the OS
default is in effect. 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: Retrieve linger period for socket shutdown¶
The XS_LINGER option shall retrieve 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: Retrieve reconnection interval¶
The XS_RECONNECT_IVL option shall retrieve 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: Retrieve maximum reconnection interval¶
The XS_RECONNECT_IVL_MAX option shall retrieve 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
transport |
XS_BACKLOG: Retrieve maximum length of the queue of outstanding connections¶
The XS_BACKLOG option shall retrieve 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¶
The option shall retrieve limit for the inbound messages. 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¶
The option shall retrieve time-to-live used for outbound multicast packets. The
default of 1 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 socket operation returns with EAGAIN¶
Retrieve the timeout for recv 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 socket operation returns with EAGAIN¶
Retrieve 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: Retrieve IPv4-only socket override status¶
Retrieve 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_FD: Retrieve file descriptor associated with the socket¶
The XS_FD option shall retrieve the file descriptor associated with the
specified socket. The returned file descriptor can be used to integrate
the socket into an existing event loop; the library shall signal any pending
events on the socket in an edge-triggered fashion by making the file
descriptor become ready for reading.
Note
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 XS_EVENTS option.
Note
The returned file descriptor is also used internally by the
xs_send and xs_recv functions. As the descriptor is edge
triggered, applications must update the state of XS_EVENTS after each
invocation of xs_send or xs_recv.To be more explicit: after
calling xs_send the socket may become readable (and vice versa)
without triggering a read event on the file descriptor.
Caution
The returned file descriptor is intended for use with a
poll or similar system call only. Applications must never attempt to
read or write data to it directly, neither should they try to close it.
Option value type |
int on POSIX systems, SOCKET on
Windows |
Option value unit |
N/A |
Default value |
N/A |
Applicable socket types |
all |
XS_EVENTS: Retrieve socket event state¶
The XS_EVENTS option shall retrieve the event state for the specified
socket. The returned value is a bit mask constructed by OR’ing a
combination of the following event flags:
XS_POLLIN
Indicates that at least one message may be received from
the specified socket without blocking.
XS_POLLOUT
Indicates that at least one message may be sent to the
specified socket without blocking.
The combination of a file descriptor returned by the XS_FD
option being ready for reading but no actual events returned by a subsequent
retrieval of the XS_EVENTS option is valid; applications should
simply ignore this case and restart their polling operation/event loop.
Option value type |
int |
Option value unit |
N/A (flags) |
Default value |
N/A |
Applicable socket types |
all |
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: Retrieve 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_getsockopt() 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, or the size
of the buffer pointed to by option_value, as specified by
option_len, is insufficient for storing the option value.
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¶
Retrieving the high water mark for outgoing messages.
/* Retrieve high water mark into sndhwm */
int sndhwm;
size_t sndhwm_size = sizeof (sndhwm);
rc = xs_getsockopt (socket, XS_SNDHWM, &sndhwm, &sndhwm_size);
assert (rc == 0);
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