|This version of this document is no longer maintained. For the latest documentation, see http://www.qnx.com/developers/docs.|
Set a queue's attributes
#include <mqueue.h> int mq_setattr( mqd_t mqdes, const struct mq_attr* mqstat, struct mq_attr* omqstat );
- The message-queue descriptor, returned by mq_open(), of the message queue that you want to set the attributes of.
- 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.
- NULL, or a pointer to a mq_attr structure where the function can store the old attributes of the message queue.
- 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,
Use the -l mq option to qcc to link against this library.
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.
|Neutrino supports two implementations of message queues: a traditional implementation, and an alternate one that uses asynchronous messages. For more information, see the entry for mq and 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:
- 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.
|The settings that you make for mq_flags apply only to the given message-queue description (i.e. locally), not to the queue itself.|
-1 if the function couldn't change the attributes (errno is set). Any other value indicates success.
- Invalid message queue mqdes.
mq, mqueue in the Utilities Reference