mq_receive - Receives the oldest, highest-priority message from the message queue (P1003.1b)
ssize_t mq_receive (
unsigned int *msg_prio);
Receives the oldest, highest-priority message from the message queue. The message is removed from the queue and transferred to the buffer pointed to by the msg_ptr argument.
If the specified message queue is empty and the O_NONBLOCK flag is not set with the mqdes argument, the mq_receive function blocks until a message is put on the queue, or until the mq_receive function is interrupted by a signal. If more than one process is waiting to receive a message when a message arrives at an empty queue, the highest-priority process that has been waiting the longest is selected to receive the message. If the message queue is empty and the O_NONBLOCK flag is set, no message is removed from the queue, and an error is returned.
On successful completion, the function returns the length of the selected message.
Otherwise, the function returns the value -1 and sets errno to indicate the error. No message is removed from the queue.
The mq_receive function fails under the following conditions:
Functions: mq_send(3) delim off