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If you consider writing a [[Microkernel]], you should layout how you'll manage the message passing. This page collects considerations on how you can do it.
==Reliable vs Unreliable MessagingBest-Effort==
;reliable
:Messages are alwaysguaranteed to be delivered unless the recipient does not exist. On failure, the sender is notified. In order to provide reliability, the message passing system ensures that messages have not been altered or corrupted betweenduring transmission and reception. Out-of-order message blocks are reordered and duplicate message blocks are removed. If an error occurs, the system will attempt to retransmit the message automatically. A message's transmission time will tend to be predictable. Reliable messagingdelivery of messages, however, usually comes with noticeable overhead.
;best-effort
;unreliable
:Messages may/may not be delivered to the recipient. If a message ''is'' delivered, its contentsit may be after a variable delay. Messages could be corrupted, out of order, or duplicated. Also, the sender maymight not receive any acknowledgment of a successful delivery. This may sound entirely useless, but unreliablebest-effort messagingdelivery is typically simpler andto fasterimplement than reliable messagingdelivery and comes with lower overhead. By puttingimplementing a reliable messagemessaging protocol on top of unreliablea messagingbest-effort delivery protocol, reliable messagingdelivery of messages can be achieved (very much like the TCP protocol[reliable] with IP packets[unreliablebest-effort]). Such a protocol might utilize "ACK" messages and timeouts to support reliable messages.
Reliable messagingdelivery is used when data ''must'' be delivered correctly bit-by-bit (as in transferring a file). UnreliableBest-effort messagingdelivery is used when lots of data must be sent quicklywith low processing overhead or when it doesn't really matter if somea few messages are corrupted or lost (like periodic "I'm alive" messages or when streaming audio/video).
==Synchronous vs Asynchronous==
What primitives will you need to get both asynchronous and synchronous message passing running? Three: send(message), receive(message) and request(message), as the send(message) primitive is/can be the same as the respond(message) primitive.
It is possible to get synchronous message passing via asynchronous message passing primitives and vice-versa. Message forwarders along with acknowledgment messages and messaging protocols can make this possible. Unfortunately, doing it this way is not efficient.
==The "Port" abstraction==
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