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grpc/load_balancing: Maintain selected subchannels in pick_first. - #3027
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nathanielford wants to merge 2 commits into
Open
nathanielford wants to merge 2 commits into
nathanielford wants to merge 2 commits into
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Motivation
When
pick_firsthas a subchannel selected, a READY report from another of its subchannels will cause it to switch to that one. This is a rare race condition, but we should prevent selected subchannels from being switched out of unless they drop the connection.Related, if a subchannel does report
Readybut there is already a subchannel selected, the LB policy should remember that it is ready and select it on a new connection pass.Solution
Add two guards:
READYnotification? If so, don't switch. Similarly, if we get failure reports from other subchannels, record those in the state cache.READYsubchannel on a connection pass start? If so, choose it.Notes