[subchannel] restructure APIs for starting a subchannel call #41009
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ctiller
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Dec 1, 2025
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A couple of nits to take care of... let's discuss landing timing offline
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| class ConnectedSubchannel; |
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Describe what these are in a comment
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| void StartCallLocked() | ||
| // Returns false if there was no connection to start a call on. | ||
| bool StartCallLocked() |
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Recommend GPR_MUST_USE_RESULT here
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This is a prerequisite for queuing calls in the subchannel, which will be needed for A105 (grpc/proposal#516).
Today, callers that need to start a call on a subchannel (primarily the client channel, but there are a couple of others) need to first ask the subchannel for the
ConnectedSubchanneland then start the call on theConnectedSubchannel. That works fine today, but when we add call queuing in the subchannel, this API would require us to acquire and release the subchannel's lock twice: once to get theConnectedSubchannel, and again to add the call to the queue.To avoid that, I have removed the
ConnectedSubchannelfrom the subchannel's API and instead made it an internal implementation detail. Instead, the subchannel itself has methods for starting a call and doing pings.This PR predominantly affects the v1 stack. There are essentially no changes to the v3 stack, since that code was already grabbing the
UnstartedCallDestinationout of theConnectedSubchannelwithin a method on the subchannel.This change is not completely trivial, but it should not cause any behavior changes, and it is sufficiently cross-cutting that I don't see an easy way to make it an experiment.