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.TH zmq_setsockopt 3 "" "(c)2007-2009 FastMQ Inc." "0MQ User Manuals"
.SH NAME
zmq_setsockopt \- sets a specified option on a 0MQ socket
.SH SYNOPSIS
.B int zmq_setsockopt (void *s, int option, const void *optval, size_t optvallen);
.SH DESCRIPTION
Sets an option on the socket.
.IR option
argument specifies the option from the list below.
.IR optval
is a pointer to the value to set,
.IR optvallen
is the size of the value in bytes.
.IP "\fBZMQ_HWM\fP"
High watermark for the message pipes associated with the socket. The water
mark cannot be exceeded. If the messages don't fit into the pipe emergency
mechanisms of the particular socket type are used (block, drop etc.) If HWM
is set to zero, there are no limits for the content of the pipe.
Type: int64_t Unit: bytes Default: 0
.IP "\fBZMQ_LWM\fP"
Low watermark makes sense only if high watermark is defined (i.e. is non-zero).
When the emergency state is reached when messages overflow the pipe, the
emergency lasts till the size of the pipe decreases to low watermark.
At that point normal state is resumed.
Type: int64_t Unit: bytes Default: 0
.IP "\fBZMQ_SWAP\fP"
Swap allows the pipe to exceed high watermark. However, the data are written
to the disk rather than held in the memory. Until high watermark is
exceeded there is no disk activity involved though. The value of the option
defines maximal size of the swap file.
Type: int64_t Unit: bytes Default: 0
.IP "\fBZMQ_AFFINITY\fP"
Affinity defines which threads in the thread pool will be used to handle
newly created sockets. This way you can dedicate some of the threads (CPUs)
to a specific work. Value of 0 means no affinity. Work is distributed
fairly among the threads in the thread pool. For non-zero values, the lowest
bit corresponds to the thread 1, second lowest bit to the thread 2 etc.
Thus, value of 3 means that from now on newly created sockets will handle
I/O activity exclusively using threads no. 1 and 2.
Type: int64_t Unit: N/A (bitmap) Default: 0
.IP "\fBZMQ_IDENTITY\fP"
Identity of the socket. Identity is important when restarting applications.
If the socket has no identity, each run of the application is completely
separated from other runs. However, with identity application reconnects to
existing infrastructure left by the previous run. Thus it may receive
messages that were sent in the meantime, it shares pipe limits with the
previous run etc.
Type: string Unit: N/A Default: NULL
.IP "\fBZMQ_SUBSCRIBE\fP"
Applicable only to ZMQ_SUB socket type. It establishes new message filter.
When ZMQ_SUB socket is created all the incoming messages are filtered out.
This option allows you to subscribe for all messages ("*"), messages with
specific topic ("x.y.z") and/or messages with specific topic prefix
("x.y.*"). Topic is one-byte-size-prefixed string located at
the very beginning of the message. Multiple filters can be attached to
a single 'sub' socket. In that case message passes if it matches at least
one of the filters.
Type: string Unit: N/A Default: N/A
.IP "\fBZMQ_UNSUBSCRIBE\fP"
Applicable only to ZMQ_SUB socket type. Removes existing message filter.
The filter specified must match the string passed to ZMQ_SUBSCRIBE options
exactly. If there were several instances of the same filter created,
this options removes only one of them, leaving the rest in place
and functional.
Type: string Unit: N/A Default: N/A
.IP "\fBZMQ_RATE\fP"
This option applies only to sending side of multicast transports (pgm & udp).
It specifies maximal outgoing data rate that an individual sender socket
can send.
Type: uint64_t Unit: kilobits/second Default: 100
.IP "\fBZMQ_RECOVERY_IVL\fP"
This option applies only to multicast transports (pgm & udp). It specifies
how long can the receiver socket survive when the sender is inaccessible.
Keep in mind that large recovery intervals at high data rates result in
very large recovery buffers, meaning that you can easily overload your box
by setting say 1 minute recovery interval at 1Gb/s rate (requires
7GB in-memory buffer).
Type: uint64_t Unit: seconds Default: 10
.IP "\fBZMQ_MCAST_LOOP\fP"
This option applies only to multicast transports (pgm & udp). Value of 1
means that the mutlicast packets can be received on the box they were sent
from. Setting the value to 0 disables the loopback functionality which
can have negative impact on the performance. If possible, disable
the loopback in production environments.
Type: uint64_t Unit: N/A (boolean value) Default: 1
.IP "\fBZMQ_SNDBUF\fP"
Sets the underlying kernel transmit buffer size to the specified size. See
.IR SO_SNDBUF
POSIX socket option. Value of zero means leaving the OS default unchanged.
Type: uint64_t Unit: bytes Default: 0
.IP "\fBZMQ_RCVBUF\fP"
Sets the underlying kernel receive buffer size to the specified size. See
.IR SO_RCVBUF
POSIX socket option. Value of zero means leaving the OS default unchanged.
Type: uint64_t Unit: bytes Default: 0
.SH RETURN VALUE
In case of success the function returns zero. Otherwise it returns -1 and
sets
.IR errno
to the appropriate value.
.SH ERRORS
.IP "\fBEINVAL\fP"
unknown option, a value with incorrect length or invalid value.
.SH EXAMPLE
.nf
int rc = zmq_setsockopt (s, ZMQ_SUBSCRIBE, "*", 1);
assert (rc == 0);
.fi
.SH SEE ALSO
.BR zmq_socket (3)
.BR zmq (7)
.SH AUTHOR
Martin Sustrik <sustrik at 250bpm dot com>
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