Move updating connectivity state outside of subchannel lock #2601
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JamesNK
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| @@ -264,6 +266,11 @@ public void RequestConnection() | |||
| } | |||
| } | |||
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| if (connectionRequested) | |||
| { | |||
| UpdateConnectivityState(ConnectivityState.Connecting, "Connection requested."); | |||
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Is this now going to cause races where someone else comes along and modifies the Subchannel state and we end up updating it to Connecting when it should stay as TransientFailure or Ready?
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I believe this is fine. The logic in load balancing is designed that state can change at any point, and other parts of the system then react to it. All other places update the connectivity state outside the subchannel lock, this one is the outlier.
BrennanConroy
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Feb 25, 2025
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Fixes #2589
In connection manager and friends there are two important types of lock:
It's safe to take a subchannel lock inside the connection manager lock, but doing the opposite can lead to a deadlock.
There is one place locks were taken in the incorrect order which could cause a deadlock in rare circumstances: the channel is pick first, it has an idle subchannel, and a connection request occurs at the same time as the resolver updates.
Repoed in a unit test:
The fix is to move the connectivity state update outside of the subchannel lock.