mq_setattr()
QNX SDP8.0C Library ReferenceAPIDeveloper
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.
Library:
libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
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. For more information, see the entry for mqueue in the Utilities Reference.
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:
| Safety: | |
|---|---|
| Cancellation point | No |
| Signal handler | No |
| Thread | Yes |
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