core: SubchannelStateListener continues to receive updates after LoadBalancer is shutdown.#5883
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zhangkun83 merged 4 commits intogrpc:masterfrom Jun 14, 2019
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…Balancer is shutdown. No more methods on the LoadBalancer will be called after LoadBalancer#shutdown() is called. This includes LoadBalancer#handleSubchannelState() too. SubchannelStateListener inherited this restriction. However, this special case makes onSubchannelState(SHUTDOWN) a unreliable way of being notified about Subchannel SHUTDOWN, and may confuse/complicate a wrapping LoadBalancer that expects the full notification. The javadoc isn't clear whether this restriction applies. I think it's more useful to make it no apply.
ejona86
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Jun 14, 2019
zhangkun83
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Jun 14, 2019
The issue: HealthCheckingLoadBalancer.shutdown() calls hcState.onSubchannelState(SHUTDOWN) which removes that hcState from helper.hcStates. Therefore, if more than one Subchannels are present, ConcurrentModificationException will be thrown. This is an alternative approach from #5848 that was reverted in #5875. Thanks to #5883, HealthCheckingLoadBalancer.shutdown() no longer has to fake SHUTDOWN notifications, and can completely rely on Subchannels' real SHUTDOWN notifications for triggering the clean-up.
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No more methods on the
LoadBalancerwill be called afterLoadBalancer#shutdown()is called. This includesLoadBalancer#handleSubchannelState()too.SubchannelStateListenerinherited this restriction. However, this special case makes
onSubchannelState(SHUTDOWN)an unreliable way of being notifiedabout
SubchannelSHUTDOWN, and may confuse/complicate awrapping
LoadBalancerthat expects the full notification (e.g., #5875).The javadoc isn't clear whether this restriction applies. I think
it's more useful to make it no apply.