Priority Messages #9269
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Priority Messages #9269
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The message queue (MQ) can now begin with a priority message queue (PMQ) where priority messages can be appended. The priority message queue is identified using a priority message queue start marker (PMQS) and a priority message queue end marker (PMQE). When a priority message is received it is inserted just before the PMQE marker. MQ -> PMQS -> PrioMsg1 -> ... -> PrioMsgN -> PMQE -> Msg1 -> ... -> MsgN The receive expression will try to match messages from the beginning of the MQ going through the messages in PMQ one by one continuing with non-priority messages when it has reached the end of the PMQ. The selective receive optimization will continue to work. When there are any receive markers present, an incoming priority message will be scanned for receive marker references. If not found, the receive can continue as usual. If a reference found in the priority message corresponds to the currently used receive marker, the priority message will be matched against before continuing with the next ordinary message. If a priority message contains a reference corresponding to a receive marker and the receive marker is used in multiple receive expressions, the second and following receive expressions will have to scan the whole PMQ before continuing to the location of the receive marker. A PMQ receive marker could be inserted preventing this. However, the PMQ is expected to be small, and it is quite unexpected that a reference is part of a priority message, so this has not been implemented.
The action performed when an ordinary message is received, is to append it to the end of the message queue. When receiving a priority marked message that action might not be taken, but instead an alternate action might be taken, i.e, the message might be appended to the end of the priority message queue. There currently exist one type of alternate action messages, namely messages sent using an alias. This commit generalize the alias message passing functionality to alternate action message passing which can be used by priority messages as well as alias messages (and potentially other future alternate action messages). Both local and distributed alternate action messages are supported.
This commit introduce functionality for registering messages that should be accepted as priority messages. Currently these types of messages can be handled as priority messages: * Priority marked messages (sent using the priority option of the send/3 BIF). The receiver registers a pid for which priority marked messages will be accepted. If the priority message is sent from the registered process, it will be accepted as a priority message; otherwise, as an ordinary message. * Exit messages. The receiver registers a pid or port for which exit signals converted to exit messages should be treated as priority messages. Both exit messages resulting from a broken link as well as exit messages resulting from a call to the exit/2 BIF will be accepted as priority messages. Other exit messages will be treated as ordinary messages. * Monitor messages, e.g., 'DOWN' messages. The receiver register a monitor reference for which the corresponding monitor message will be treated as a priority message. Other monitor messages will be treated as ordinary messages. With this commit priority messages will also actually be delivered into the priority message queue implemented in an earlier commit.
garazdawi
requested review from
garazdawi,
kikofernandez,
lucioleKi and
frazze-jobb
|
I really like the consolidation of the various dist operations for sending a message down to |
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Reference implementation for EEP 76 (pull request 73) on the eep repository.