java: client cancels, but StatusRuntimeException not thrown on the server

[Piotr Morgwai Kotarbinski]

Hi all,

I have a simplest possible server-streaming method:

service CancelService {

rpc fun(Empty) returns (stream Empty) {}

}

an implementation that sleeps for 1s and then sends reply:

public class CancelService extends CancelServiceImplBase {

@Override

public void fun(Empty request, StreamObserver<Empty> basicResponseObserver) {

final var responseObserver = (ServerCallStreamObserver<Empty>) basicResponseObserver;

try {

Thread.sleep(1000l);  // longer than client's deadline

System.out.println("isCancelled: " + responseObserver.isCancelled());

responseObserver.onNext(request);

responseObserver.onCompleted();

System.out.println("completed successfully");

} catch (StatusRuntimeException e) {

System.out.println("StatusRuntimeException" + e);

} catch (Throwable t) {

System.out.println("server error" + t);

responseObserver.onError(Status.INTERNAL.withCause(t).asException());

if (t instanceof Error) throw (Error) t;

}

}

public static void main(String[] args) throws Exception {

final Server server = NettyServerBuilder

.forPort(6666)

.addService(new CancelService())

.build()

.start();

Runtime.getRuntime().addShutdownHook(new Thread(() -> {

try { server.shutdown().awaitTermination(5, TimeUnit.SECONDS); } catch (Exception e) {}

}));

System.out.println("server started");

server.awaitTermination();

}

}

and a client that sets deadline to 0.5s:

public static void main(String[] args) throws Exception {

final var channel = ManagedChannelBuilder

.forTarget("localhost:6666")

.usePlaintext()

.build();

final var connector = CancelServiceGrpc.newBlockingStub(channel)

.withDeadlineAfter(500l, TimeUnit.MILLISECONDS);

final var results = connector.fun(Empty.newBuilder().build());

while (results.hasNext()) {

System.out.println("got result: " + results.next());

}

System.out.println("call successful");

}

when run, on the client side I get an excp as expected:

Exception in thread "main" io.grpc.StatusRuntimeException: DEADLINE_EXCEEDED: deadline exceeded (...)

on the server however, responseObserver.isCancelled() returns true but StatusRuntimeException is not thrown when calling onNext(...) and onCompleted() and call finishes as normal:

server started

isCancelled: true

completed successfully

is this an expected behavior? I thought StatusRuntimeException with Status.CANCELLED should be thrown, no? (unless onCancelHandler is set, which is not the case here)

To make things more confusing, if I dispatch work in fun(...) to some executor like this:

ThreadPoolExecutor executor =

new ThreadPoolExecutor(3, 3, 0, TimeUnit.DAYS, new LinkedBlockingQueue<>());

@Override

public void fun(Empty request, StreamObserver<Empty> basicResponseObserver) {

final var responseObserver = (ServerCallStreamObserver<Empty>) basicResponseObserver;

executor.execute(() -> {

try {

Thread.sleep(1000l);  // longer than client's deadline

System.out.println("isCancelled: " + responseObserver.isCancelled());

responseObserver.onNext(request);

responseObserver.onCompleted();

System.out.println("completed successfully");

} catch (StatusRuntimeException e) {

System.out.println("StatusRuntimeException" + e);

} catch (Throwable t) {

System.out.println("server error" + t);

responseObserver.onError(Status.INTERNAL.withCause(t).asException());

if (t instanceof Error) throw (Error) t;

}

});

}

then I do get a StatusRuntimeException:

server started

isCancelled: true

StatusRuntimeExceptionio.grpc.StatusRuntimeException: CANCELLED: call already cancelled. Use ServerCallStreamObserver.setOnCancelHandler() to disable this exception

Shouldn't the behavior be consistent in both of these cases?

Thanks!

 

[Piotr Morgwai Kotarbinski]

I've looked into the source and now I can see why it happens. I think it's a bug so filed an issue with exact description what should be fixed: https://github.com/grpc/grpc-java/issues/8409