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Clarify the ServerCallHandler API contract. #8339

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merged 4 commits into from Jul 26, 2021
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Clarify the ServerCallHandler API contract. #8339

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df64d79
Clarify the ServerCallHandler API contract.
jdcormie Jul 23, 2021
970a13e
Discuss responsibility to close()
jdcormie Jul 23, 2021
cd0b931
in particular
jdcormie Jul 23, 2021
54cb5df
remove "next stage"
jdcormie Jul 26, 2021
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23 changes: 16 additions & 7 deletions api/src/main/java/io/grpc/ServerCallHandler.java
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Expand Up @@ -25,17 +25,26 @@
@ThreadSafe
public interface ServerCallHandler<RequestT, ResponseT> {
/**
* Produce a non-{@code null} listener for the incoming call. Implementations are free to call
* methods on {@code call} before this method has returned.
* Passes {@code call} on to the next stage of asynchronous processing.
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*
* <p>Since {@link Metadata} is not thread-safe, the caller must not access (read or write) {@code
* headers} after this point.
* <p>Callers of this method transfer their ownership of the non-thread-safe {@link ServerCall}
* and {@link Metadata} arguments to the {@link ServerCallHandler} implementation for processing.
* Ownership means that the implementation may invoke methods on {@code call} and {@code headers}
* while {@link #startCall} runs and at any time after it returns normally. On the other hand, if
* {@link #startCall} throws, ownership of {@code call} and {@code headers} reverts to the caller
* and the implementation loses the right to call methods on these objects (from some other
* thread, say).
*
* <p>If the implementation throws an exception, {@code call} will be closed with an error.
* Implementations must not throw an exception if they started processing that may use {@code
* call} on another thread.
* <p>Ownership also includes the responsibility to eventually close {@code call}. In particular,
* if {@link #startCall} throws an exception, the caller must handle it by closing {@code call}
* with an error. Since {@code call} can only be closed once, an implementation can report errors
* either to {@link ServerCall#close} for itself or by throwing an exception, but not both.
*
* <p>Returns a non-{@code null} listener for the incoming call. Callers of this method must
* arrange for events associated with {@code call} to be delivered there.
*
* @param call object for responding to the remote client.
* @param headers request headers received from the client but open to modification by an owner
* @return listener for processing incoming request messages for {@code call}
*/
ServerCall.Listener<RequestT> startCall(
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