Simplify getting a hostinfo or starting a handshake with one #954
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wadey
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We had a rare deadlock in GetOrHandshake because we kept the hostmap lock when we do the call to StartHandshake. StartHandshake can block while sending to the lighthouse query worker channel, and that worker needs to be able to grab the hostmap lock to do its work. Other calls for StartHandshake don't hold the hostmap lock so we should be able to drop it here. This lock was originally added with: #954
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We had a rare deadlock in GetOrHandshake because we kept the hostmap lock when we do the call to StartHandshake. StartHandshake can block while sending to the lighthouse query worker channel, and that worker needs to be able to grab the hostmap lock to do its work. Other calls for StartHandshake don't hold the hostmap lock so we should be able to drop it here. This lock was originally added with: #954
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This PR is based on #953. The base branch will be changed to
masterwhen it merges.The goal here is to simplify getting a hostinfo and starting a handshake, paving the way to invert how handshake state is tracked so that we don't have to keep all of it around in a fully formed hostinfo.
This should also resolve the last remaining racy issues with interactions between the pending and main hostmap.
There are 2 trouble spots here.
HandshakeManager.allocateIndexacquires a main hostmap read lock and a pending hostmap write lock while it holds a hostinfo lock. I haven't found anywhere where that order is violated yet but it's worth some extra eyes.handshake_ix.gois inherently racy, I think it's a little better now than it was before but solving it entirely requires inverting the interactions withHandshakeManager.