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SPDX-License-Identifier: CC-BY-SA-4.0
copyrights:
- Copyright (C) 2021 embedded brains GmbH (http://www.embedded-brains.de)
enabled-by: true
glossary-type: term
links:
- role: glossary-member
uid: group
term: first message
text: |
Messages are stored - and kept - in a ${/glossary/messagequeue:/term}
in a defined order: Mgs[0], Mgs[1], Mgs[2] till Msg[N-1] when N
messages are in the queue. Mgs[0] is named the *first message*. Msg[N-1]
is named the *last message*.
${../if/receive:/name} returns the first message (if the
${/glossary/messagequeue:/term} is not empty). The
receive operation removes the first message (Msg[0]) from the queue
so that N-1 messages are in the queue. The remaining messages change
place so that "old" message Msg[i] becomes "new" Msg[i-1].
Messages are stored by ${../if/send:/name} in a
${/glossary/messagequeue:/term} in ${/glossary/fifo:/term} order
(if no ${../if/receive:/name} directive is waiting to receive a
message). ${../if/send:/name} adds the message as "new" last message
Msg[N] to the queue and the number of messages in the queue increases
by one: N+1.
In contrast, messages are stored by ${../if/urgent:/name} in a
${/glossary/messagequeue:/term} in ${/glossary/lifo:/term} order
(if no ${../if/receive:/name} directive is waiting to receive a
message). ${../if/urgent:/name} adds the message as "new" first message
Msg[0] to the queue. The messages which have been in the queue before
change place so that "old" message Msg[i] becomes "new" Msg[i+1] and the
number of messages in the queue increases by one: N+1.
type: glossary
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