ZMQ_CTX_SET(3) 0MQ Manual 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.
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.
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.
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 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.
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.
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.
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.
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
zmq_ctx_get(3) using the ZMQ_MAX_MSGSZ option.
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 zmq_ctx_get(3) using the ZMQ_ZERO_COPY_RECV option.
NOTE: in DRAFT state, not yet available in stable releases.
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
zmq_ctx_get(3) using the ZMQ_SOCKET_LIMIT option.
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.
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
zmq_ctx_get(3) zmq(7)
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0MQ 4.3.4 01/18/2023 ZMQ_CTX_SET(3)
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