= zmq_ctx_set(3)


== NAME

zmq_ctx_set - set context options


== SYNOPSIS
*int zmq_ctx_set (void '*context', int 'option_name', int 'option_value');*


== DESCRIPTION
The _zmq_ctx_set()_ function shall set the option specified by the
'option_name' argument to the value of the 'option_value' argument.

The _zmq_ctx_set()_ function accepts the following options:


ZMQ_BLOCKY: Fix blocky behavior
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
By default the context will block, forever, on a zmq_ctx_term call. The
assumption behind this behavior is that abrupt termination will cause
message loss. Most real applications use some form of handshaking to ensure
applications receive termination messages, and then terminate the context
with 'ZMQ_LINGER' set to zero on all sockets. This setting is an easier way
to get the same result. When 'ZMQ_BLOCKY' is set to false, all new sockets
are given a linger timeout of zero. You must still close all sockets before
calling zmq_ctx_term.

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Default value:: true (old behavior)


ZMQ_IO_THREADS: Set number of I/O threads
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_IO_THREADS' argument specifies the size of the 0MQ thread pool to
handle I/O operations. If your application is using only the 'inproc'
transport for messaging you may set this to zero, otherwise set it to at
least one. This option only applies before creating any sockets on the
context.

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Default value:: 1


ZMQ_THREAD_SCHED_POLICY: Set scheduling policy for I/O threads
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_THREAD_SCHED_POLICY' argument sets the scheduling policy for
internal context's thread pool. This option is not available on windows.
Supported values for this option can be found in sched.h file,
or at http://man7.org/linux/man-pages/man2/sched_setscheduler.2.html.
This option only applies before creating any sockets on the context.

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Default value:: -1


ZMQ_THREAD_PRIORITY: Set scheduling priority for I/O threads
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_THREAD_PRIORITY' argument sets scheduling priority for
internal context's thread pool. This option is not available on windows.
Supported values for this option depend on chosen scheduling policy.
On Linux, when the scheduler policy is SCHED_OTHER, SCHED_IDLE or SCHED_BATCH, the OS scheduler
will not use the thread priority but rather the thread "nice value"; in such cases,
if 'ZMQ_THREAD_PRIORITY' is set to a strictly positive value,
the system call "nice" will be used to set the nice value to -20 (max priority) instead of
adjusting the thread priority (which must be zero for those scheduling policies).
Details can be found in sched.h file, or at http://man7.org/linux/man-pages/man2/sched_setscheduler.2.html.
This option only applies before creating any sockets on the context.

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Default value:: -1


ZMQ_THREAD_AFFINITY_CPU_ADD: Add a CPU to list of affinity for I/O threads
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_THREAD_AFFINITY_CPU_ADD' argument adds a specific CPU to the affinity list for the internal
context's thread pool. This option is only supported on Linux.
This option only applies before creating any sockets on the context.
The default affinity list is empty and means that no explicit CPU-affinity will be set on
internal context's threads.

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Default value:: -1


ZMQ_THREAD_AFFINITY_CPU_REMOVE: Remove a CPU to list of affinity for I/O threads
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_THREAD_AFFINITY_CPU_REMOVE' argument removes a specific CPU to the affinity list for the internal
context's thread pool. This option is only supported on Linux.
This option only applies before creating any sockets on the context.
The default affinity list is empty and means that no explicit CPU-affinity will be set on
internal context's threads.

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Default value:: -1


ZMQ_THREAD_NAME_PREFIX: Set name prefix for I/O threads
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_THREAD_NAME_PREFIX' argument sets a numeric prefix to each thread
created for the internal context's thread pool. This option is only supported on Linux.
This option is useful to help  debugging done via "top -H" or "gdb"; in case
multiple processes on the system are using ZeroMQ it is useful to provide through
this context option an application-specific prefix to distinguish ZeroMQ background
threads that belong to different processes.
This option only applies before creating any sockets on the context.

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Default value:: -1



ZMQ_MAX_MSGSZ: Set maximum message size
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_MAX_MSGSZ' argument sets the maximum allowed size
of a message sent in the context. You can query the maximal
allowed value with xref:zmq_ctx_get.adoc[zmq_ctx_get] using the
'ZMQ_MAX_MSGSZ' option.

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Default value:: INT_MAX
Maximum value:: INT_MAX


ZMQ_ZERO_COPY_RECV: Specify message decoding strategy
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_ZERO_COPY_RECV' argument specifies whether the message decoder should
use a zero copy strategy when receiving messages. The zero copy strategy can
lead to increased memory usage in some cases. This option allows you to use the
older copying strategy. You can query the value of this option with
xref:zmq_ctx_get.adoc[zmq_ctx_get] using the 'ZMQ_ZERO_COPY_RECV' option.
NOTE: in DRAFT state, not yet available in stable releases.

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Default value:: 1


ZMQ_MAX_SOCKETS: Set maximum number of sockets
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_MAX_SOCKETS' argument sets the maximum number of sockets allowed
on the context. You can query the maximal allowed value with
xref:zmq_ctx_get.adoc[zmq_ctx_get] using the 'ZMQ_SOCKET_LIMIT' option.

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Default value:: 1023


ZMQ_IPV6: Set IPv6 option
~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_IPV6' argument sets the IPv6 value for all sockets created in
the context from this point onwards. A value of `1` means IPv6 is
enabled, while `0` means the socket will use only IPv4. When IPv6 is
enabled, a socket will connect to, or accept connections from, both
IPv4 and IPv6 hosts.

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Default value:: 0


== RETURN VALUE
The _zmq_ctx_set()_ function returns zero if successful. Otherwise it
returns `-1` and sets 'errno' to one of the values defined below.


== ERRORS
*EINVAL*::
The requested option _option_name_ is unknown.


== EXAMPLE
.Setting a limit on the number of sockets
----
void *context = zmq_ctx_new ();
zmq_ctx_set (context, ZMQ_MAX_SOCKETS, 256);
int max_sockets = zmq_ctx_get (context, ZMQ_MAX_SOCKETS);
assert (max_sockets == 256);
----


== SEE ALSO
* xref:zmq_ctx_get.adoc[zmq_ctx_get]
* xref:zmq.adoc[zmq]


== AUTHORS
This page was written by the 0MQ community. To make a change please
read the 0MQ Contribution Policy at <https://zeromq.org/how-to-contribute/>.
