Explaination of ENOMSG in k_msgq_put

[ClaytonNorthey92]

Looking at the k_msgq_put documentation, I notice that the following error can be returned with the accompanying definition:

-ENOMSG – Returned without waiting or queue purged.

What does "Returned without waiting" mean? Does that mean the message was handled without it waiting in the queue?

[JordanYates]

Because message queues can only hold a fixed number of messages, it is possible that the queue is already full when you call k_msgq_put.
If this is the case, but you also specified not to wait at all (via K_NO_WAIT), -ENOMSG is returned.

zephyr/kernel/msg_q.c

Lines 155 to 158 in 62f19cc

	} else if (K_TIMEOUT_EQ(timeout, K_NO_WAIT)) {
	/* don't wait for message space to become available */
	result = -ENOMSG;
	} else {