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xds: Fix intermittent failure in RingHashLoadBalancerTest.allSubchannelsInTransientFailure - #13130
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…elsInTransientFailure Deliver TRANSIENT_FAILURE in deterministic server order using subchannelList instead of iterating over subchannels.values() (HashMap), and expect 2 connections. Why this became flaky with the new PickFirst LB: Old PickFirst unconditionally invoked subchannel.requestConnection() on each call without checking connection state, so triggering proactive connections twice always produced 2 connection requests regardless of iteration order (either [A, B] or [A, A]). New PickFirst deduplicates connection requests if a subchannel is already in CONNECTING state. When iterating over a HashMap, if the same subchannel was triggered twice, New PickFirst deduplicated it to 1 connection, leading to the assumption in grpc#13094 that New PickFirst would always yield 1 connection. However, if two distinct subchannels were triggered (e.g. server1 then server2), New PickFirst does not deduplicate and yields 2 connections, causing verifyConnection(1) to fail intermittently. Fix this by iterating deterministically in server order, which reliably triggers two distinct subchannels (server1 and server2) in both old and new PickFirst. TAG=agy CONV=d59ec8a0-3bb7-41f8-bb11-76e843a2dada
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Oct 26, 2026
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Deliver TRANSIENT_FAILURE in deterministic server order using subchannelList instead of iterating over subchannels.values() (HashMap), and expect 2 connections.
Why this became flaky with the new PickFirst LB:
Old PickFirst unconditionally invoked subchannel.requestConnection() on each call without checking connection state, so triggering proactive connections twice always produced 2 connection requests regardless of iteration order (either [A, B] or [A, A]).
New PickFirst deduplicates connection requests if a subchannel is already in CONNECTING state. When iterating over a HashMap, if the same subchannel was triggered twice, New PickFirst deduplicated it to 1 connection, leading to the assumption in #13094 that New PickFirst would always yield 1 connection. However, if two distinct subchannels were triggered (e.g. server1 then server2), New PickFirst does not deduplicate and yields 2 connections, causing verifyConnection(1) to fail intermittently.
Fix this by iterating deterministically in server order, which reliably triggers two distinct subchannels (server1 and server2) in both old and new PickFirst.
Failure test run in fusion2/d9446b33-dc0e-4dee-b901-ea9b3b57f3c6