mq_send - Places a message in the message queue (P1003.1b)
int mq_send (
const char *msg_ptr,
unsigned int msg_prio);
Places a message in the message queue. This function inserts the message in the queue at the position indicated by the msg_prio argument. A message with a relatively large numeric value for the msg_prio argument has a high priority, and it is therefore inserted before messages with lower values for the msg_prio argument. This function inserts messages with equal priority into the queue in first-in/first-out order. Thus the function inserts a message with a given priority after already-queued messages that have the same priority.
If the message queue is full, and the O_NONBLOCK flag associated with it is not set, the mq_send function blocks until either sufficient space in the message queue becomes available or a signal interrupts the mq_send function.
If two or more processes are waiting to send messages when space becomes available in the queue, the highest priority process that has been waiting the longest sends the message first.
The mq_send function returns an error indication if the specified queue is full and the O_NONBLOCK flag is set for that queue.
On successful completion, the mq_send function returns a value of zero.
Otherwise, no message is sent, -1 is returned, and errno is set to indicate the error.
The mq_send function fails under the following conditions:
Functions: mq_receive(3), mq_setattr(3) delim off