|This version of this document is no longer maintained. For the latest documentation, see http://www.qnx.com/developers/docs.|
Send a message to a queue
#include <mqueue.h> int mq_send( mqd_t mqdes, const char * msg_ptr, size_t msg_len, unsigned int msg_prio );
- The message-queue descriptor, returned by mq_open(), of the message queue that you want to send a message to.
- A pointer to the message that you want to send.
- The size of the message.
- The priority of the message, in the range from 0 to (MQ_PRIO_MAX-1).
- 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_send() function puts a message of size msg_len and pointed to by msg_ptr into the queue indicated by mqdes. The new message has a priority of msg_prio.
|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.|
The queue is maintained in priority order, and in FIFO order within the same priority.
If the number of elements on the specified queue is equal to its mq_maxmsg, and O_NONBLOCK wasn't set (in the oflag argument to mq_open()), the call to mq_send() blocks. It becomes unblocked when there's room on the queue to send the given message. If more than one mq_send() is blocked on a given queue, and space becomes available in that queue to send, then the mq_send() with the highest priority message is unblocked.
In the traditional (mqueue) implementation, calling write() with mqdes is analogous to calling mq_send() with a msg_prio of 0.
-1 if an error occurred (errno is set). Any other value indicates success.
- The O_NONBLOCK flag was set when opening the queue, and the specified queue is full.
- The mqdes argument doesn't represent a valid message queue descriptor, or mqdes wasn't opened for writing.
- The call was interrupted by a signal.
- One of the following cases is true:
- msg_len was negative
- msg_prio was greater than (MQ_PRIO_MAX-1)
- msg_prio was less than 0
- The msg_len argument was greater than the msgsize associated with the specified queue.
mq, mqueue in the Utilities Reference