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5db69f1b41
Changelog-Changed: `fundchannel_cancel` will now succeed even when executed while a `fundchannel_complete` is ongoing; in that case, it will be considered as cancelling the funding *after* the `fundchannel_complete` succeeds.
Let me introduce the concept of "Sequential Consistency":
All operations on parallel processes form a single total order agreed upon by all processes.
So for example, suppose we have parallel invocations of `fundchannel_complete` and `fundchannel_cancel`:
+--[fundchannel_complete]-->
|
--[fundchannel_start]-+
|
+--[fundchannel_cancel]---->
What "Sequential Consistency" means is that the above parallel operations can be serialized as a single total order as:
--[fundchannel_start]--[fundchannel_complete]--[fundchannel_cancel]-->
Or:
--[fundchannel_start]--[fundchannel_cancel]--[fundchannel_complete]-->
In the first case, `fundchannel_complete` succeeds, and the `fundchannel_cancel` invocation also succeeds, sending an `error` to the peer to make them forget the chanel.
In the second case, `fundchannel_cancel` succeeds, and the succeeding `fundchannel_complete` invocation fails, since the funding is already cancelled and there is nothing to complete.
Note that in both cases, `fundchannel_cancel` **always** succeeds.
Unfortunately, prior to this commit, `fundchannel_cancel` could fail with a `Try fundchannel_cancel again` error if the `fundchannel_complete` is ongoing when the `fundchannel_cancel` is initiated.
This violates Sequential Consistency, as there is no single total order that would have caused `fundchannel_cancel` to fail.
This commit is a minimal patch which just reschedules `fundchannel_cancel` to occur after any `fundchannel_complete` that is ongoing.