'\" t
.\"     Title: zmq_ctx_set
.\"    Author: [see the "AUTHORS" section]
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\"      Date: 10/23/2023
.\"    Manual: 0MQ Manual
.\"    Source: 0MQ 4.3.5
.\"  Language: English
.\"
.TH "ZMQ_CTX_SET" "3" "10/23/2023" "0MQ 4\&.3\&.5" "0MQ Manual"
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.SH "NAME"
zmq_ctx_set \- set context options
.SH "SYNOPSIS"
.sp
\fBint zmq_ctx_set (void \fR\fB\fI*context\fR\fR\fB, int \fR\fB\fIoption_name\fR\fR\fB, int \fR\fB\fIoption_value\fR\fR\fB);\fR
.SH "DESCRIPTION"
.sp
The \fIzmq_ctx_set()\fR function shall set the option specified by the \fIoption_name\fR argument to the value of the \fIoption_value\fR argument\&.
.sp
The \fIzmq_ctx_set()\fR function accepts the following options:
.SS "ZMQ_BLOCKY: Fix blocky behavior"
.sp
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 \fIZMQ_LINGER\fR set to zero on all sockets\&. This setting is an easier way to get the same result\&. When \fIZMQ_BLOCKY\fR 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\&.
.TS
tab(:);
lt lt.
T{
.sp
Default value
T}:T{
.sp
true (old behavior)
T}
.TE
.sp 1
.SS "ZMQ_IO_THREADS: Set number of I/O threads"
.sp
The \fIZMQ_IO_THREADS\fR argument specifies the size of the 0MQ thread pool to handle I/O operations\&. If your application is using only the \fIinproc\fR 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\&.
.TS
tab(:);
lt lt.
T{
.sp
Default value
T}:T{
.sp
1
T}
.TE
.sp 1
.SS "ZMQ_THREAD_SCHED_POLICY: Set scheduling policy for I/O threads"
.sp
The \fIZMQ_THREAD_SCHED_POLICY\fR argument sets the scheduling policy for internal context\(cqs thread pool\&. This option is not available on windows\&. Supported values for this option can be found in sched\&.h file, or at \m[blue]\fBhttp://man7\&.org/linux/man\-pages/man2/sched_setscheduler\&.2\&.html\fR\m[]\&. This option only applies before creating any sockets on the context\&.
.TS
tab(:);
lt lt.
T{
.sp
Default value
T}:T{
.sp
\-1
T}
.TE
.sp 1
.SS "ZMQ_THREAD_PRIORITY: Set scheduling priority for I/O threads"
.sp
The \fIZMQ_THREAD_PRIORITY\fR argument sets scheduling priority for internal context\(cqs 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 \fIZMQ_THREAD_PRIORITY\fR 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 \m[blue]\fBhttp://man7\&.org/linux/man\-pages/man2/sched_setscheduler\&.2\&.html\fR\m[]\&. This option only applies before creating any sockets on the context\&.
.TS
tab(:);
lt lt.
T{
.sp
Default value
T}:T{
.sp
\-1
T}
.TE
.sp 1
.SS "ZMQ_THREAD_AFFINITY_CPU_ADD: Add a CPU to list of affinity for I/O threads"
.sp
The \fIZMQ_THREAD_AFFINITY_CPU_ADD\fR argument adds a specific CPU to the affinity list for the internal context\(cqs 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\(cqs threads\&.
.TS
tab(:);
lt lt.
T{
.sp
Default value
T}:T{
.sp
\-1
T}
.TE
.sp 1
.SS "ZMQ_THREAD_AFFINITY_CPU_REMOVE: Remove a CPU to list of affinity for I/O threads"
.sp
The \fIZMQ_THREAD_AFFINITY_CPU_REMOVE\fR argument removes a specific CPU to the affinity list for the internal context\(cqs 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\(cqs threads\&.
.TS
tab(:);
lt lt.
T{
.sp
Default value
T}:T{
.sp
\-1
T}
.TE
.sp 1
.SS "ZMQ_THREAD_NAME_PREFIX: Set name prefix for I/O threads"
.sp
The \fIZMQ_THREAD_NAME_PREFIX\fR argument sets a numeric prefix to each thread created for the internal context\(cqs 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\&.
.TS
tab(:);
lt lt.
T{
.sp
Default value
T}:T{
.sp
\-1
T}
.TE
.sp 1
.SS "ZMQ_MAX_MSGSZ: Set maximum message size"
.sp
The \fIZMQ_MAX_MSGSZ\fR argument sets the maximum allowed size of a message sent in the context\&. You can query the maximal allowed value with \fBzmq_ctx_get\fR(3) using the \fIZMQ_MAX_MSGSZ\fR option\&.
.TS
tab(:);
lt lt
lt lt.
T{
.sp
Default value
T}:T{
.sp
INT_MAX
T}
T{
.sp
Maximum value
T}:T{
.sp
INT_MAX
T}
.TE
.sp 1
.SS "ZMQ_ZERO_COPY_RECV: Specify message decoding strategy"
.sp
The \fIZMQ_ZERO_COPY_RECV\fR 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 \fBzmq_ctx_get\fR(3) using the \fIZMQ_ZERO_COPY_RECV\fR option\&. NOTE: in DRAFT state, not yet available in stable releases\&.
.TS
tab(:);
lt lt.
T{
.sp
Default value
T}:T{
.sp
1
T}
.TE
.sp 1
.SS "ZMQ_MAX_SOCKETS: Set maximum number of sockets"
.sp
The \fIZMQ_MAX_SOCKETS\fR argument sets the maximum number of sockets allowed on the context\&. You can query the maximal allowed value with \fBzmq_ctx_get\fR(3) using the \fIZMQ_SOCKET_LIMIT\fR option\&.
.TS
tab(:);
lt lt.
T{
.sp
Default value
T}:T{
.sp
1023
T}
.TE
.sp 1
.SS "ZMQ_IPV6: Set IPv6 option"
.sp
The \fIZMQ_IPV6\fR 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\&.
.TS
tab(:);
lt lt.
T{
.sp
Default value
T}:T{
.sp
0
T}
.TE
.sp 1
.SH "RETURN VALUE"
.sp
The \fIzmq_ctx_set()\fR function returns zero if successful\&. Otherwise it returns \-1 and sets \fIerrno\fR to one of the values defined below\&.
.SH "ERRORS"
.PP
\fBEINVAL\fR
.RS 4
The requested option
\fIoption_name\fR
is unknown\&.
.RE
.SH "EXAMPLE"
.PP
\fBSetting a limit on the number of sockets\fR. 
.sp
.if n \{\
.RS 4
.\}
.nf
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);
.fi
.if n \{\
.RE
.\}
.sp
.SH "SEE ALSO"
.sp
\fBzmq_ctx_get\fR(3) \fBzmq\fR(7)
.SH "AUTHORS"
.sp
This page was written by the 0MQ community\&. To make a change please read the 0MQ Contribution Policy at \m[blue]\fBhttp://www\&.zeromq\&.org/docs:contributing\fR\m[]\&.