Commits on Sep 28, 2023

1. peer: launch persistent peer pruning in background goroutine …

   This PR is a follow up, to a [follow
   up](lightningnetwork#7938) of an [initial
   concurrency issue](lightningnetwork#7856)
   fixed in the peer goroutine.
   
   In lightningnetwork#7938, we noticed that the introduction of `p.startReady` can cause
   `Disconnect` to block. This happens as `Disconnect` cannot be called
   until `p.startReady` has been closed. `Disconnect` is also called from
   `InboundPeerConnected` (the case of concurrent peers, so we need to
   remove one of the connections) while the main server mutex is held. If
   `p.Start` blocks for any reason, then this leads to the deadlock as: we
   can't disconnect until we've finished starting, and we can't finish
   starting as we need the disconnect caller to exit as it has the mutex.
   
   In this commit, we now make the call to `prunePersistentPeerConnection`
   async. The call to `prunePersistentPeerConnection` eventually wants to
   grab the server mutex, which triggers the circular waiting scenario
   above.
   
   The main learning here is that no calls to the main server mutex path
   can block from `p.Start`. This is more or less a stop gap to resolve the
   issue initially introduced in v0.16.4. Assuming we want to move forward
   with this fix, we should reexamine `p.startReady` all together, and also
   revisit attempt to refactor this section of the code to eliminate the
   mega mutex in the server in favor of a dedicated event loop.

   

   Roasbeef committed Sep 28, 2023
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