mq_setattr()

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:

For the traditional implementation, libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
For the alternate implementation using asynchronous messages, libmq
Use the -l mq option to qcc to link against this library.

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: QNX Neutrino supports two implementations of message queues: a traditional implementation, and an alternate one that uses asynchronous messages. For more information, see the entries for mq and mqueue in the Utilities Reference, as well as the Managing POSIX Message Queues 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