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https://issues.apache.org/jira/browse/MESOS-3870?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14998700#comment-14998700
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haosdent commented on MESOS-3870:
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Suppose a Process enqueue to runq twice(Or impossible, seems I could not find
any code avoid it enqueue multi times) when it receive two events.
And the dequeue in different work threads, and not yet running. In work thread
1, Process dequeue event A and not yet running. In work thread 2, Process
dequeue event B and start running.
Is this scenario possible?
> Prevent out-of-order libprocess message delivery
> ------------------------------------------------
>
> Key: MESOS-3870
> URL: https://issues.apache.org/jira/browse/MESOS-3870
> Project: Mesos
> Issue Type: Bug
> Components: libprocess
> Reporter: Neil Conway
> Priority: Minor
> Labels: mesosphere
>
> I was under the impression that {{send()}} provided in-order, unreliable
> message delivery. So if P1 sends <M1,M2> to P2, P2 might see <>, <M1>, <M2>,
> or <M1,M2> — but not <M2,M1>.
> I suspect much of the code makes a similar assumption. However, it appears
> that this behavior is not guaranteed. slave.cpp:2217 has the following
> comment:
> {noformat}
> // TODO(jieyu): Here we assume that CheckpointResourcesMessages are
> // ordered (i.e., slave receives them in the same order master sends
> // them). This should be true in most of the cases because TCP
> // enforces in order delivery per connection. However, the ordering
> // is technically not guaranteed because master creates multiple
> // connections to the slave in some cases (e.g., persistent socket
> // to slave breaks and master uses ephemeral socket). This could
> // potentially be solved by using a version number and rejecting
> // stale messages according to the version number.
> {noformat}
> We can improve this situation by _either_: (1) fixing libprocess to guarantee
> ordered message delivery, e.g., by adding a sequence number, or (2)
> clarifying that ordered message delivery is not guaranteed, and ideally
> providing a tool to force messages to be delivered out-of-order.
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