core: throw away subchannel references after round_robin is shutdown (v1.37.x backport) #8155
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…rpc#8132) Triggering balancing state updates after already being shutdown can be confusing for the upstream of round_robin. In cases of the callers not managing round_robin's lifecycle (e.g., not ignoring updates after it shuts down round_robin, which it should), it can make problem very bad, especially with the behavior that round_robin is actually propagating TRANSIENT_FAILURE with a picker that buffers RPCs. This change only polishes round_robin by always preserving its invariant. Callers/LBs should not rely on this and should still manage the balancing updates from its downstream correctly based on the downstream's lifetime.
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/cc @ericgribkoff |
dapengzhang0
approved these changes
May 10, 2021
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Triggering balancing state updates after already being shutdown can be confusing for the upstream of round_robin. In cases of the callers not managing round_robin's lifecycle (e.g., not ignoring updates after it shuts down round_robin, which it should), it can make problem very bad, especially with the behavior that round_robin is actually propagating TRANSIENT_FAILURE with a picker that buffers RPCs.
This change only polishes round_robin by always preserving its invariant. Callers/LBs should not rely on this and should still manage the balancing updates from its downstream correctly based on the downstream's lifetime.
Backport of #8132