Set a queue's attributes
Synopsis:
#include <mqueue.h>
int mq_setattr( mqd_t mqdes,
const struct mq_attr* mqstat,
struct mq_attr* omqstat );
Arguments:
- mqdes
- The message-queue descriptor, returned by
mq_open(),
of the message queue that you want to set the attributes of.
- mqstat
- A pointer to a mq_attr structure that specifies the
attributes that you want to use for the message queue.
For more information about this structure, see
mq_getattr();
for information about which attributes you can set, see below.
- omqstat
- NULL, or a pointer to a mq_attr structure
where the function can store the old attributes of the message queue.
Description:
The mq_setattr() function sets the
mq_flags field for the specified queue (passed as the
mq_flags field in mqstat). If
omqstat isn't NULL, then the old attribute
structure is stored in the location that it points to.
Note: The message queue manager needs to be running.
QNX Neutrino supports two
implementations of message queues: a traditional implementation, and an alternate one that uses the
mq server and a queue in kernel space. For more information, see the entries for
mq and
mqueue
in the
Utilities Reference, as well as the
POSIX Message Queues: Two Implementations
technote.
This function ignores the mq_maxmsg, mq_msgsize, and
mq_curmsgs fields of mqstat.
The mq_flags field is the
bitwise OR of zero or more of the following constants:
- O_NONBLOCK
- No
mq_receive()
or
mq_send()
will ever block on this queue.
If the queue is in such a condition that the given
operation can't be performed without blocking, then an error is
returned, and errno is set to EAGAIN.
Note:
The settings that you make for mq_flags apply only to the
given message-queue description (i.e., locally), not to the queue itself.
Returns:
-1 if the function couldn't change the attributes
(errno
is set).
Any other value indicates success.
Errors:
- EBADF
- Invalid message queue mqdes.
Classification:
POSIX 1003.1 MSG
Safety: |
|
Cancellation point |
No |
Interrupt handler |
No |
Signal handler |
No |
Thread |
Yes |