Alternate message queue manager (QNX Neutrino)
Note:
You must be root or have the right abilities to start this manager.
Syntax:
mq [-d] [-m num_msgs] [-N path] [-s size] [-U string]
Options:
- -d
- Don't daemonize.
- -m num_msgs
- Set the default for the maximum number of messages, for use if the mq_attr argument to
mq_open()
is NULL.
The default is 64 messages.
- -N path
- Set the pathname of the directory for message queues.
The default is /dev/mq.
- -s size
- Set the default message size, for use if the mq_attr argument to
mq_open() is NULL.
The default is 256 bytes.
- -U user_name
- -U uid[:gid[,sup_gid]*]]
- (QNX Neutrino 6.6 or later)
Once running, run as the specified user, so that the program doesn't need to run as root:
- In the first form, the service sets itself to be the named user and uses that user's groups.
This form depends on the /etc/passwd and /etc/group files.
- In the second form, the service sets its user ID, and optionally its group ID and
supplementary groups, to the values provided.
Description:
The mq manager is an alternate implementation of POSIX 1003.1b message queues.
When you create a queue, it appears in the pathname space under /dev/mq.
Note:
- In QNX Neutrino 7.0 or later, mq and the traditional message queue manager
(mqueue)
can coexist, but we recommend that you use only one of them on your system.
-
You can change this directory to union over the directory exported by
the mqueue server by using the mq -N/dev/mqueue
option, but we don't recommend this, because it may cause some user-namespace confusion.
This implementation uses a queue within the kernel to buffer the messages and eliminates the
context-switching overheads of using an external server (i.e., mqueue) in
each message-queue operation, thus greatly improving the performance of POSIX message
queues.
In order to use the mq implementation, you must link your application(s)
against the libmq library.
In a manual build, specify the -l mq option; in automatic/recursive builds,
use this setting in your common.mk file:
LIBS += mq
For more information, see the
POSIX Message Queues: Two Implementations
technote.