Add an RPC cancellation handler #2090
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Motivation: As a service author it's useful to know if the RPC has been cancelled (because it's timed out, the remote peer closed it, the connection dropped etc). For cases where the stream has already closed this can be surfaced by a read or write failing. However, for cases like server-streaming RPCs where there are no reads and writes can be infrequent it's useful to have a more explicit signal. Modifications: - Add a `ServerCancellationManager`, this is internal per-stream storage for registering cancellation handlers and storing whether the RPC has been cancelled. - Add the `RPCCancellationHandle` nested within the `ServerContext`. This holds an instance of the manager and provides higher level APIs allowing users to check if the RPC has been cancellation and to wait until the RPC has been cancelled. - Add a top-level `withRPCCancellationHandler` which registers a callback with the manager. - Add a top-level `withServerContextRPCCancellationHandle` for creating and binding the task local manager. This is intended for use by transport implementations rather than users. - Update the in-process transport to cancel RPCs when shutting down gracefully. - Update the server executor to cancel RPCs when the timeout fires. Result: Users can watch for cancellation using `withRPCCancellationHandler`.
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gjcairo
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Oct 9, 2024
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Looks good, thanks George. Left only a few minor comments.
| private let newStreamsContinuation: AsyncStream<RPCStream<Inbound, Outbound>>.Continuation | ||
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| private struct State: Sendable { | ||
| private var id: UInt64 |
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Can we maybe call this nextHandleID or something like that?
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| /// the duration of the RPC. This function is intended for use when implementing | ||
| /// a ``ServerTransport``. |
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Can we maybe put the second sentence inside an Important block? I think it could be misused.
gjcairo
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Motivation:
As a service author it's useful to know if the RPC has been cancelled (because it's timed out, the remote peer closed it, the connection dropped etc).
For cases where the stream has already closed this can be surfaced by a read or write failing. However, for cases like server-streaming RPCs where there are no reads and writes can be infrequent it's useful to have a more explicit signal.
Modifications:
ServerCancellationManager, this is internal per-stream storage for registering cancellation handlers and storing whether the RPC has been cancelled.RPCCancellationHandlenested within theServerContext. This holds an instance of the manager and provides higher level APIs allowing users to check if the RPC has been cancellation and to wait until the RPC has been cancelled.withRPCCancellationHandlerwhich registers a callback with the manager.withServerContextRPCCancellationHandlefor creating and binding the task local manager. This is intended for use by transport implementations rather than users.Result:
Users can watch for cancellation using
withRPCCancellationHandler.