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.
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.
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.
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.
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.
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.
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_RCV: Specify message decoding strategy¶
The ZMQ_ZERO_COPY_RCV 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.
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.
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.
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);
