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);
SEE ALSO¶
xs_setsockopt(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