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238 lines
8.0 KiB
Plaintext
238 lines
8.0 KiB
Plaintext
zmq_getsockopt(3)
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=================
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NAME
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----
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zmq_getsockopt - get 0MQ socket options
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SYNOPSIS
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--------
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*int zmq_getsockopt (void '*socket', int 'option_name', void '*option_value', size_t '*option_len');*
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DESCRIPTION
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-----------
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The _zmq_getsockopt()_ function shall retrieve the value for the option
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specified by the 'option_name' argument for the 0MQ socket pointed to by the
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'socket' argument, and store it in the buffer pointed to by the 'option_value'
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argument. The 'option_len' argument is the size in bytes of the buffer pointed
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to by 'option_value'; upon successful completion _zmq_getsockopt()_ shall
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modify the 'option_len' argument to indicate the actual size of the option
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value stored in the buffer.
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The following options can be retrieved with the _zmq_getsockopt()_ function:
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ZMQ_RCVMORE: More message parts to follow
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The 'ZMQ_RCVMORE' option shall return a boolean value indicating if the
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multi-part message currently being read from the specified 'socket' has more
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message parts to follow. If there are no message parts to follow or if the
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message currently being read is not a multi-part message a value of zero shall
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be returned. Otherwise, a value of 1 shall be returned.
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Refer to linkzmq:zmq_send[3] and linkzmq:zmq_recv[3] for a detailed description
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of sending/receiving multi-part messages.
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[horizontal]
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Option value type:: int64_t
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Option value unit:: boolean
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Default value:: N/A
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Applicable socket types:: all
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ZMQ_HWM: Retrieve high water mark
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The 'ZMQ_HWM' option shall retrieve the high water mark for the specified
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'socket'. The high water mark is a hard limit on the maximum number of
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outstanding messages 0MQ shall queue in memory for any single peer that the
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specified 'socket' is communicating with.
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If this limit has been reached the socket shall enter an exceptional state and
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depending on the socket type, 0MQ shall take appropriate action such as
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blocking or dropping sent messages. Refer to the individual socket descriptions
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in linkzmq:zmq_socket[3] for details on the exact action taken for each socket
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type.
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The default 'ZMQ_HWM' value of zero means "no limit".
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[horizontal]
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Option value type:: int64_t
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Option value unit:: messages
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Default value:: 0
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Applicable socket types:: all
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ZMQ_SWAP: Retrieve disk offload size
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The 'ZMQ_SWAP' option shall retrieve the disk offload (swap) size for the
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specified 'socket'. A socket which has 'ZMQ_SWAP' set to a non-zero value may
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exceed it's high water mark; in this case outstanding messages shall be
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offloaded to storage on disk rather than held in memory.
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The value of 'ZMQ_SWAP' defines the maximum size of the swap space in bytes.
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[horizontal]
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Option value type:: int64_t
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Option value unit:: bytes
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Default value:: 0
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Applicable socket types:: all
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ZMQ_AFFINITY: Retrieve I/O thread affinity
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The 'ZMQ_AFFINITY' option shall retrieve the I/O thread affinity for newly
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created connections on the specified 'socket'.
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Affinity determines which threads from the 0MQ I/O thread pool associated with
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the socket's _context_ shall handle newly created connections. A value of zero
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specifies no affinity, meaning that work shall be distributed fairly among all
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0MQ I/O threads in the thread pool. For non-zero values, the lowest bit
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corresponds to thread 1, second lowest bit to thread 2 and so on. For example,
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a value of 3 specifies that subsequent connections on 'socket' shall be handled
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exclusively by I/O threads 1 and 2.
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See also linkzmq:zmq_init[3] for details on allocating the number of I/O
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threads for a specific _context_.
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[horizontal]
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Option value type:: int64_t
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Option value unit:: N/A (bitmap)
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Default value:: 0
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Applicable socket types:: N/A
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ZMQ_IDENTITY: Retrieve socket identity
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The 'ZMQ_IDENTITY' option shall retrieve the identity of the specified
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'socket'. Socket identity determines if existing 0MQ infastructure (_message
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queues_, _forwarding devices_) shall be identified with a specific application
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and persist across multiple runs of the application.
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If the socket has no identity, each run of an application is completely
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separate from other runs. However, with identity set the socket shall re-use
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any existing 0MQ infrastructure configured by the previous run(s). Thus the
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application may receive messages that were sent in the meantime, _message
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queue_ limits shall be shared with previous run(s) and so on.
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Identity can be at least one byte and at most 255 bytes long. Identities
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starting with binary zero are reserved for use by 0MQ infrastructure.
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[horizontal]
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Option value type:: binary data
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Option value unit:: N/A
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Default value:: NULL
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Applicable socket types:: all
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ZMQ_RATE: Retrieve multicast data rate
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The 'ZMQ_RATE' option shall retrieve the maximum send or receive data rate for
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multicast transports using the specified 'socket'.
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[horizontal]
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Option value type:: uint64_t
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Option value unit:: kilobits per second
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Default value:: 100
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Applicable socket types:: all, when using multicast transports
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ZMQ_RECOVERY_IVL: Get multicast recovery interval
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The 'ZMQ_RECOVERY_IVL' option shall retrieve the recovery interval for
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multicast transports using the specified 'socket'. The recovery interval
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determines the maximum time in seconds that a receiver can be absent from a
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multicast group before unrecoverable data loss will occur.
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[horizontal]
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Option value type:: uint64_t
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Option value unit:: seconds
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Default value:: 10
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Applicable socket types:: all, when using multicast transports
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ZMQ_MCAST_LOOP: Control multicast loopback
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The 'ZMQ_MCAST_LOOP' option controls whether data sent via multicast
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transports can also be received by the sending host via loopback. A value of
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zero indicates that the loopback functionality is disabled, while the default
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value of 1 indicates that the loopback functionality is enabled. Leaving
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multicast loopback enabled when it is not required can have a negative impact
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on performance. Where possible, disable 'ZMQ_MCAST_LOOP' in production
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environments.
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[horizontal]
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Option value type:: uint64_t
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Option value unit:: boolean
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Default value:: 1
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Applicable socket types:: all, when using multicast transports
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ZMQ_SNDBUF: Retrieve kernel transmit buffer size
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The 'ZMQ_SNDBUF' option shall retrieve the underlying kernel transmit buffer
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size for the specified 'socket'. A value of zero means that the OS default is
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in effect. For details refer to your operating system documentation for the
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'SO_SNDBUF' socket option.
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[horizontal]
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Option value type:: uint64_t
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Option value unit:: bytes
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Default value:: 0
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Applicable socket types:: all
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ZMQ_RCVBUF: Retrieve kernel receive buffer size
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The 'ZMQ_RCVBUF' option shall retrieve the underlying kernel receive buffer
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size for the specified 'socket'. A value of zero means that the OS default is
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in effect. For details refer to your operating system documentation for the
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'SO_RCVBUF' socket option.
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[horizontal]
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Option value type:: uint64_t
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Option value unit:: bytes
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Default value:: 0
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Applicable socket types:: all
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RETURN VALUE
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------------
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The _zmq_getsockopt()_ function shall return zero if successful. Otherwise it
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shall return `-1` and set 'errno' to one of the values defined below.
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ERRORS
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------
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*EINVAL*::
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The requested option _option_name_ is unknown, or the requested _option_len_ or
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_option_value_ is invalid, or the size of the buffer pointed to by
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_option_value_, as specified by _option_len_, is insufficient for storing the
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option value.
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*ETERM*::
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The 0MQ 'context' associated with the specified 'socket' was terminated.
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EXAMPLE
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-------
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.Retrieving the high water mark
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----
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/* Retrieve high water mark into hwm */
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int64_t hwm;
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size_t hwm_size = sizeof (hwm);
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rc = zmq_getsockopt (socket, ZMQ_HWM, &hwm, &hwm_size);
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assert (rc == 0);
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----
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SEE ALSO
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--------
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linkzmq:zmq_setsockopt[3]
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linkzmq:zmq_socket[3]
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linkzmq:zmq[7]
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