[Java] Clean way to detect client crash

[julien...@sonarsource.com]

Hi,

We are using grpc for C# <-> Java integration. The C# client application will start the Java process containing the grpc server, and then create a Chanel used for calling methods on Java server side.

One problem we have is to properly terminate the Java server in case the C# client crashed badly. In the current state, the Java process keeps running in the background forever.

Is there a way to be notified on server side when a client died?

Thanks

Julien

[Eric Anderson]

I'd suggest the C# client creates a long-running RPC to the Java server, and the RPC will be seen as cancelled on the server when the connection is broken. I don't believe you need it in your case, but in similar cases you'd want to enable keepalive on the server-side.

[julien...@sonarsource.com]

Hi Eric,

Thanks for your idea. Here is how I have implemented it, tell me if this is correct:

rpc HeartBeat(stream Void) returns Void;

C# Client do:

using (var heartBeat = client.HeartBeat(new CallOptions(null, null, channel.ShutdownToken).WithWaitForReady(true)))
{
    await heartBeat.ResponseAsync;
}

On Java server side:

 

  @Override
  public StreamObserver<Void> heartBeat(StreamObserver<Void> responseObserver) {
    return new StreamObserver<Void>() {

      @Override
      public void onNext(Void value) {
        // Nothing to do
      }

      @Override
      public void onError(Throwable t) {
        shutdown();
      }

      @Override
      public void onCompleted() {
        shutdown();
      }
    };
  }

Does it seems correct for you? Why would have to enable keepalive?

Thanks,

Julien

[Eric Anderson]

On Wed, Jul 12, 2017 at 2:59 AM, <julien...@sonarsource.com> wrote:

Thanks for your idea. Here is how I have implemented it, tell me if this is correct:

Yeah. That looked good.

Why would have to enable keepalive?

If a connection doesn't have any writes then TCP won't be able to detect breakages. So I normally recommend enabling keepalive when you have a long-lived stream with little activity, as it will trigger writes. However, in your case you are local, so we'd expect the connection to be reliable and provide a prompt notification if the connection is closed (and thus keepalive probably is unnecessary).