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<body>
<div id="header">
<h1>
zmq_setsockopt(3) Manual Page
</h1>
<h2>NAME</h2>
<div class="sectionbody">
<p>zmq_setsockopt -
   set 0MQ socket options
</p>
</div>
</div>
<div id="content">
<h2 id="_synopsis">SYNOPSIS</h2>
<div class="sectionbody">
<div class="paragraph"><p><strong>int zmq_setsockopt (void <em>*socket</em>, int <em>option_name</em>, const void <em>*option_value</em>, size_t <em>option_len</em>);</strong></p></div>
<div class="paragraph"><p>Caution: All options, with the exception of ZMQ_SUBSCRIBE, ZMQ_UNSUBSCRIBE and
ZMQ_LINGER, only take effect for subsequent socket bind/connects.</p></div>
</div>
<h2 id="_description">DESCRIPTION</h2>
<div class="sectionbody">
<div class="paragraph"><p>The <em>zmq_setsockopt()</em> function shall set the option specified by the
<em>option_name</em> argument to the value pointed to by the <em>option_value</em> argument
for the ØMQ socket pointed to by the <em>socket</em> argument. The <em>option_len</em>
argument is the size of the option value in bytes.</p></div>
<div class="paragraph"><p>The following socket options can be set with the <em>zmq_setsockopt()</em> function:</p></div>
<h3 id="_zmq_hwm_set_high_water_mark">ZMQ_HWM: Set high water mark</h3><div style="clear:left"></div>
<div class="paragraph"><p>The <em>ZMQ_HWM</em> option shall set the high water mark for the specified <em>socket</em>.
The high water mark is a hard limit on the maximum number of outstanding
messages ØMQ shall queue in memory for any single peer that the specified
<em>socket</em> is communicating with.</p></div>
<div class="paragraph"><p>If this limit has been reached the socket shall enter an exceptional state and
depending on the socket type, ØMQ shall take appropriate action such as
blocking or dropping sent messages. Refer to the individual socket descriptions
in <a href="zmq_socket.html">zmq_socket(3)</a> for details on the exact action taken for each socket
type.</p></div>
<div class="paragraph"><p>The default <em>ZMQ_HWM</em> value of zero means "no limit".</p></div>
<div class="hdlist"><table>
<tr>
<td class="hdlist1">
Option value type
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
uint64_t
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Option value unit
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
messages
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Default value
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
0
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Applicable socket types
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
all
</p>
</td>
</tr>
</table></div>
<h3 id="_zmq_swap_set_disk_offload_size">ZMQ_SWAP: Set disk offload size</h3><div style="clear:left"></div>
<div class="paragraph"><p>The <em>ZMQ_SWAP</em> option shall set the disk offload (swap) size for the specified
<em>socket</em>. A socket which has <em>ZMQ_SWAP</em> set to a non-zero value may exceed its
high water mark; in this case outstanding messages shall be offloaded to
storage on disk rather than held in memory.</p></div>
<div class="paragraph"><p>The value of <em>ZMQ_SWAP</em> defines the maximum size of the swap space in bytes.</p></div>
<div class="hdlist"><table>
<tr>
<td class="hdlist1">
Option value type
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
int64_t
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Option value unit
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
bytes
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Default value
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
0
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Applicable socket types
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
all
</p>
</td>
</tr>
</table></div>
<h3 id="_zmq_affinity_set_i_o_thread_affinity">ZMQ_AFFINITY: Set I/O thread affinity</h3><div style="clear:left"></div>
<div class="paragraph"><p>The <em>ZMQ_AFFINITY</em> option shall set the I/O thread affinity for newly created
connections on the specified <em>socket</em>.</p></div>
<div class="paragraph"><p>Affinity determines which threads from the ØMQ I/O thread pool associated with
the socket&#8217;s <em>context</em> shall handle newly created connections.  A value of zero
specifies no affinity, meaning that work shall be distributed fairly among all
ØMQ 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 <em>socket</em> shall be handled
exclusively by I/O threads 1 and 2.</p></div>
<div class="paragraph"><p>See also <a href="zmq_init.html">zmq_init(3)</a> for details on allocating the number of I/O
threads for a specific <em>context</em>.</p></div>
<div class="hdlist"><table>
<tr>
<td class="hdlist1">
Option value type
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
uint64_t
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Option value unit
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
N/A (bitmap)
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Default value
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
0
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Applicable socket types
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
N/A
</p>
</td>
</tr>
</table></div>
<h3 id="_zmq_identity_set_socket_identity">ZMQ_IDENTITY: Set socket identity</h3><div style="clear:left"></div>
<div class="paragraph"><p>The <em>ZMQ_IDENTITY</em> option shall set the identity of the specified <em>socket</em>.
Socket identity determines if existing ØMQ infrastructure (<em>message queues</em>,
<em>forwarding devices</em>) shall be identified with a specific application and
persist across multiple runs of the application.</p></div>
<div class="paragraph"><p>If the socket has no identity, each run of an application is completely
separate from other runs. However, with identity set the socket shall re-use
any existing ØMQ infrastructure configured by the previous run(s). Thus the
application may receive messages that were sent in the meantime, <em>message
queue</em> limits shall be shared with previous run(s) and so on.</p></div>
<div class="paragraph"><p>Identity should be at least one byte and at most 255 bytes long. Identities
starting with binary zero are reserved for use by ØMQ infrastructure.</p></div>
<div class="hdlist"><table>
<tr>
<td class="hdlist1">
Option value type
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
binary data
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Option value unit
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
N/A
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Default value
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
NULL
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Applicable socket types
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
all
</p>
</td>
</tr>
</table></div>
<h3 id="_zmq_subscribe_establish_message_filter">ZMQ_SUBSCRIBE: Establish message filter</h3><div style="clear:left"></div>
<div class="paragraph"><p>The <em>ZMQ_SUBSCRIBE</em> option shall establish a new message filter on a <em>ZMQ_SUB</em>
socket. Newly created <em>ZMQ_SUB</em> sockets shall filter out all incoming messages,
therefore you should call this option to establish an initial message filter.</p></div>
<div class="paragraph"><p>An empty <em>option_value</em> of length zero shall subscribe to all incoming
messages. A non-empty <em>option_value</em> shall subscribe to all messages beginning
with the specified prefix. Multiple filters may be attached to a single
<em>ZMQ_SUB</em> socket, in which case a message shall be accepted if it matches at
least one filter.</p></div>
<div class="hdlist"><table>
<tr>
<td class="hdlist1">
Option value type
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
binary data
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Option value unit
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
N/A
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Default value
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
N/A
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Applicable socket types
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
ZMQ_SUB
</p>
</td>
</tr>
</table></div>
<h3 id="_zmq_unsubscribe_remove_message_filter">ZMQ_UNSUBSCRIBE: Remove message filter</h3><div style="clear:left"></div>
<div class="paragraph"><p>The <em>ZMQ_UNSUBSCRIBE</em> option shall remove an existing message filter on a
<em>ZMQ_SUB</em> socket. The filter specified must match an existing filter previously
established with the <em>ZMQ_SUBSCRIBE</em> option. If the socket has several
instances of the same filter attached the <em>ZMQ_UNSUBSCRIBE</em> option shall remove
only one instance, leaving the rest in place and functional.</p></div>
<div class="hdlist"><table>
<tr>
<td class="hdlist1">
Option value type
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
binary data
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Option value unit
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
N/A
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Default value
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
N/A
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Applicable socket types
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
ZMQ_SUB
</p>
</td>
</tr>
</table></div>
<h3 id="_zmq_rate_set_multicast_data_rate">ZMQ_RATE: Set multicast data rate</h3><div style="clear:left"></div>
<div class="paragraph"><p>The <em>ZMQ_RATE</em> option shall set the maximum send or receive data rate for
multicast transports such as <a href="zmq_pgm.html">zmq_pgm(7)</a> using the specified <em>socket</em>.</p></div>
<div class="hdlist"><table>
<tr>
<td class="hdlist1">
Option value type
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
int64_t
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Option value unit
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
kilobits per second
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Default value
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
100
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Applicable socket types
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
all, when using multicast transports
</p>
</td>
</tr>
</table></div>
<h3 id="_zmq_recovery_ivl_set_multicast_recovery_interval">ZMQ_RECOVERY_IVL: Set multicast recovery interval</h3><div style="clear:left"></div>
<div class="paragraph"><p>The <em>ZMQ_RECOVERY_IVL</em> option shall set the recovery interval for multicast
transports using the specified <em>socket</em>. The recovery interval determines the
maximum time in seconds that a receiver can be absent from a multicast group
before unrecoverable data loss will occur.</p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<div class="title">Caution</div>
</td>
<td class="content">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.</td>
</tr></table>
</div>
<div class="hdlist"><table>
<tr>
<td class="hdlist1">
Option value type
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
int64_t
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Option value unit
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
seconds
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Default value
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
10
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Applicable socket types
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
all, when using multicast transports
</p>
</td>
</tr>
</table></div>
<h3 id="_zmq_recovery_ivl_msec_set_multicast_recovery_interval_in_milliseconds">ZMQ_RECOVERY_IVL_MSEC: Set multicast recovery interval in milliseconds</h3><div style="clear:left"></div>
<div class="paragraph"><p>The <em>ZMQ_RECOVERY_IVL_MSEC</em> option shall set the recovery interval, specified
in milliseconds (ms) for multicast transports using the specified <em>socket</em>.
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.</p></div>
<div class="paragraph"><p>A non-zero value of the <em>ZMQ_RECOVERY_IVL_MSEC</em> option will take precedence
over the <em>ZMQ_RECOVERY_IVL</em> option, but since the default for the
<em>ZMQ_RECOVERY_IVL_MSEC</em> is -1, the default is to use the <em>ZMQ_RECOVERY_IVL</em>
option value.</p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<div class="title">Caution</div>
</td>
<td class="content">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.</td>
</tr></table>
</div>
<div class="hdlist"><table>
<tr>
<td class="hdlist1">
Option value type
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
int64_t
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Option value unit
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
milliseconds
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Default value
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
-1
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Applicable socket types
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
all, when using multicast transports
</p>
</td>
</tr>
</table></div>
<h3 id="_zmq_mcast_loop_control_multicast_loop_back">ZMQ_MCAST_LOOP: Control multicast loop-back</h3><div style="clear:left"></div>
<div class="paragraph"><p>The <em>ZMQ_MCAST_LOOP</em> option shall control whether data sent via multicast
transports using the specified <em>socket</em> can also be received by the sending
host via loop-back. A value of zero disables the loop-back functionality, while
the default value of 1 enables the loop-back functionality. Leaving multicast
loop-back enabled when it is not required can have a negative impact on
performance. Where possible, disable <em>ZMQ_MCAST_LOOP</em> in production
environments.</p></div>
<div class="hdlist"><table>
<tr>
<td class="hdlist1">
Option value type
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
int64_t
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Option value unit
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
boolean
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Default value
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
1
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Applicable socket types
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
all, when using multicast transports
</p>
</td>
</tr>
</table></div>
<h3 id="_zmq_sndbuf_set_kernel_transmit_buffer_size">ZMQ_SNDBUF: Set kernel transmit buffer size</h3><div style="clear:left"></div>
<div class="paragraph"><p>The <em>ZMQ_SNDBUF</em> option shall set the underlying kernel transmit buffer size
for the <em>socket</em> 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 <em>SO_SNDBUF</em> socket option.</p></div>
<div class="hdlist"><table>
<tr>
<td class="hdlist1">
Option value type
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
uint64_t
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Option value unit
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
bytes
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Default value
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
0
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Applicable socket types
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
all
</p>
</td>
</tr>
</table></div>
<h3 id="_zmq_rcvbuf_set_kernel_receive_buffer_size">ZMQ_RCVBUF: Set kernel receive buffer size</h3><div style="clear:left"></div>
<div class="paragraph"><p>The <em>ZMQ_RCVBUF</em> option shall set the underlying kernel receive buffer size for
the <em>socket</em> 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 <em>SO_RCVBUF</em> socket option.</p></div>
<div class="hdlist"><table>
<tr>
<td class="hdlist1">
Option value type
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
uint64_t
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Option value unit
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
bytes
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Default value
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
0
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Applicable socket types
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
all
</p>
</td>
</tr>
</table></div>
<h3 id="_zmq_linger_set_linger_period_for_socket_shutdown">ZMQ_LINGER: Set linger period for socket shutdown</h3><div style="clear:left"></div>
<div class="paragraph"><p>The <em>ZMQ_LINGER</em> option shall set the linger period for the specified <em>socket</em>.
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
<a href="zmq_close.html">zmq_close(3)</a>, and further affects the termination of the socket&#8217;s
context with <a href="zmq_term.html">zmq_term(3)</a>. The following outlines the different
behaviours:</p></div>
<div class="ulist"><ul>
<li>
<p>
The default value of <em>-1</em> specifies an infinite linger period. Pending
  messages shall not be discarded after a call to <em>zmq_close()</em>; attempting to
  terminate the socket&#8217;s context with <em>zmq_term()</em> shall block until all
  pending messages have been sent to a peer.
</p>
</li>
<li>
<p>
The value of <em>0</em> specifies no linger period. Pending messages shall be
  discarded immediately when the socket is closed with <em>zmq_close()</em>.
</p>
</li>
<li>
<p>
Positive values specify an upper bound for the linger period in milliseconds.
  Pending messages shall not be discarded after a call to <em>zmq_close()</em>;
  attempting to terminate the socket&#8217;s context with <em>zmq_term()</em> 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.
</p>
<div class="hdlist"><table>
<tr>
<td class="hdlist1">
Option value type
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
int
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Option value unit
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
milliseconds
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Default value
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
-1 (infinite)
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Applicable socket types
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
all
</p>
</td>
</tr>
</table></div>
</li>
</ul></div>
<h3 id="_zmq_reconnect_ivl_set_reconnection_interval">ZMQ_RECONNECT_IVL: Set reconnection interval</h3><div style="clear:left"></div>
<div class="paragraph"><p>The <em>ZMQ_RECONNECT_IVL</em> option shall set the initial reconnection interval for
the specified <em>socket</em>.  The reconnection interval is the period ØMQ
shall wait between attempts to reconnect disconnected peers when using
connection-oriented transports.</p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">The reconnection interval may be randomized by ØMQ to prevent
reconnection storms in topologies with a large number of peers per socket.</td>
</tr></table>
</div>
<div class="hdlist"><table>
<tr>
<td class="hdlist1">
Option value type
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
int
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Option value unit
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
milliseconds
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Default value
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
100
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Applicable socket types
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
all, only for connection-oriented transports
</p>
</td>
</tr>
</table></div>
<h3 id="_zmq_reconnect_ivl_max_set_maximum_reconnection_interval">ZMQ_RECONNECT_IVL_MAX: Set maximum reconnection interval</h3><div style="clear:left"></div>
<div class="paragraph"><p>The <em>ZMQ_RECONNECT_IVL_MAX</em> option shall set the maximum reconnection interval
for the specified <em>socket</em>.  This is the maximum period ØMQ shall wait between
attempts to reconnect. On each reconnect attempt, the previous interval shall be
doubled untill ZMQ_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 ZMQ_RECONNECT_IVL.</p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">Values less than ZMQ_RECONNECT_IVL will be ignored.</td>
</tr></table>
</div>
<div class="hdlist"><table>
<tr>
<td class="hdlist1">
Option value type
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
int
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Option value unit
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
milliseconds
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Default value
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
0 (only use ZMQ_RECONNECT_IVL)
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Applicable socket types
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
all, only for connection-oriented transports
</p>
</td>
</tr>
</table></div>
<h3 id="_zmq_backlog_set_maximum_length_of_the_queue_of_outstanding_connections">ZMQ_BACKLOG: Set maximum length of the queue of outstanding connections</h3><div style="clear:left"></div>
<div class="paragraph"><p>The <em>ZMQ_BACKLOG</em> option shall set the maximum length of the queue of
outstanding peer connections for the specified <em>socket</em>; this only applies to
connection-oriented transports. For details refer to your operating system
documentation for the <em>listen</em> function.</p></div>
<div class="hdlist"><table>
<tr>
<td class="hdlist1">
Option value type
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
int
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Option value unit
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
connections
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Default value
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
100
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Applicable socket types
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
all, only for connection-oriented transports.
</p>
</td>
</tr>
</table></div>
</div>
<h2 id="_return_value">RETURN VALUE</h2>
<div class="sectionbody">
<div class="paragraph"><p>The <em>zmq_setsockopt()</em> function shall return zero if successful. Otherwise it
shall return <tt>-1</tt> and set <em>errno</em> to one of the values defined below.</p></div>
</div>
<h2 id="_errors">ERRORS</h2>
<div class="sectionbody">
<div class="dlist"><dl>
<dt class="hdlist1">
<strong>EINVAL</strong>
</dt>
<dd>
<p>
The requested option <em>option_name</em> is unknown, or the requested <em>option_len</em> or
<em>option_value</em> is invalid.
</p>
</dd>
<dt class="hdlist1">
<strong>ETERM</strong>
</dt>
<dd>
<p>
The ØMQ <em>context</em> associated with the specified <em>socket</em> was terminated.
</p>
</dd>
<dt class="hdlist1">
<strong>ENOTSOCK</strong>
</dt>
<dd>
<p>
The provided <em>socket</em> was invalid.
</p>
</dd>
<dt class="hdlist1">
<strong>EINTR</strong>
</dt>
<dd>
<p>
The operation was interrupted by delivery of a signal.
</p>
</dd>
</dl></div>
</div>
<h2 id="_example">EXAMPLE</h2>
<div class="sectionbody">
<div class="listingblock">
<div class="title">Subscribing to messages on a <em>ZMQ_SUB</em> socket</div>
<div class="content">
<pre><tt>/* Subscribe to all messages */
rc = zmq_setsockopt (socket, ZMQ_SUBSCRIBE, "", 0);
assert (rc == 0);
/* Subscribe to messages prefixed with "ANIMALS.CATS" */
rc = zmq_setsockopt (socket, ZMQ_SUBSCRIBE, "ANIMALS.CATS", 12);</tt></pre>
</div></div>
<div class="listingblock">
<div class="title">Setting I/O thread affinity</div>
<div class="content">
<pre><tt>int64_t affinity;
/* Incoming connections on TCP port 5555 shall be handled by I/O thread 1 */
affinity = 1;
rc = zmq_setsockopt (socket, ZMQ_AFFINITY, &amp;affinity, sizeof affinity);
assert (rc);
rc = zmq_bind (socket, "tcp://lo:5555");
assert (rc);
/* Incoming connections on TCP port 5556 shall be handled by I/O thread 2 */
affinity = 2;
rc = zmq_setsockopt (socket, ZMQ_AFFINITY, &amp;affinity, sizeof affinity);
assert (rc);
rc = zmq_bind (socket, "tcp://lo:5556");
assert (rc);</tt></pre>
</div></div>
</div>
<h2 id="_see_also">SEE ALSO</h2>
<div class="sectionbody">
<div class="paragraph"><p><a href="zmq_getsockopt.html">zmq_getsockopt(3)</a>
<a href="zmq_socket.html">zmq_socket(3)</a>
<a href="zmq.html">zmq(7)</a></p></div>
</div>
<h2 id="_authors">AUTHORS</h2>
<div class="sectionbody">
<div class="paragraph"><p>This ØMQ manual page was written by Martin Sustrik &lt;<a href="mailto:sustrik@250bpm.com">sustrik@250bpm.com</a>&gt; and
Martin Lucina &lt;<a href="mailto:mato@kotelna.sk">mato@kotelna.sk</a>&gt;.</p></div>
</div>
</div>
<div id="footnotes"><hr /></div>
<div id="footer">
<div id="footer-text">
ØMQ 2.1.10<br />
Last updated 2011-08-23 16:01:49 CDT
</div>
</div>
</body>
</html>