core: reference-count shared transport factory for OOB channels - #12985
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kannanjgithub merged 2 commits intoAug 13, 2026
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When a main channel enters IDLE mode (e.g. after 30 minutes of inactivity), it shuts down its Load Balancer (such as RLS or xDS). This in turn shuts down any Out-of-Band (OOB) child channels created by the LB. Previously, when an OOB channel finished terminating, it called `transportFactory.close()`, which prematurely closed the parent channel's shared `ClientTransportFactory` (`NettyTransportFactory`). As a result, when the main channel later attempted to exit IDLE mode or reconnect, `transportFactory.newClientTransport()` threw `IllegalStateException: The transport factory is closed`, causing an uncaught exception panic in the SynchronizationContext. This change introduces `RefCountedClientTransportFactory` to track active references to the underlying `ClientTransportFactory`. When OOB channels inherit `originalTransportFactory` via `createResolvingOobChannelBuilder()`, `retain()` is invoked. Calling `close()` on the transport factory now decrements the reference count, ensuring the underlying delegate factory is only closed when all parent and child channel references have been released.
ejona86
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Aug 12, 2026
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I'm not wild about needing to refcount, but I agree that is very appropriate for now. We should come back to the non-ChannelCredentials code paths at some point and see if we can reduce how often they occur.
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| public ClientTransportFactory buildClientTransportFactory() { | ||
| return transportFactory; |
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This shows we really didn't think about the lifetimes involved here. We are relying on the caller actually building the returned builder (to avoid leaking the transport factory) and to not build multiple times.
callCredentials prevents us from trivially moving the transportFactory creation into this method. We should revisit this code at some point to see if we can make it sound.
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Added a TODO for now.
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When a main channel enters IDLE mode (e.g. after 30 minutes of inactivity), it shuts down its Load Balancer (such as RLS). This in turn shuts down any Out-of-Band child channels created by the LB. Previously, when an OOB channel finished terminating, it called
transportFactory.close(), which prematurely closed the parent channel's sharedClientTransportFactory(NettyTransportFactory). As a result, when the main channel later attempted to exit IDLE mode or reconnect,transportFactory.newClientTransport()threwIllegalStateException: The transport factory is closed, causing an uncaught exception panic in the SynchronizationContext.This change introduces
RefCountedClientTransportFactoryto track active references to the underlyingClientTransportFactory. When OOB channels inheritoriginalTransportFactoryviacreateResolvingOobChannelBuilder(),retain()is invoked. Callingclose()on the transport factory now decrements the reference count, ensuring the underlying delegate factory is only closed when all parent and child channel references have been released.b/545260270