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 );
Use the -l c option to qcc to link against this library. This library is usually included automatically.
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.
|The message queue manager needs to be running. 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.|
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.
POSIX 1003.1 MSG
mq_close(), mq_open(), mq_receive(), mq_timedsend()
mq, mqueue in the Utilities Reference
“POSIX message queues” in the “Interprocess Communication (IPC)” chapter of System Architecture
POSIX Message Queues: Two Implementations technote.