How can I close Channel when using Interceptors

[Martin Grześlowski]

Hi!

Normally when I was using stubs I was creating ChannelImpl (by NettyChannelBuilder) and then when program ends I used channelImpl.shutdown(). Below is some code snippet for thath use case:

ChannelImpl channel = NettyChannelBuilder.<...>.build();
Service.ServiceStub stub = Service.newStub(channel);
...do some stuf with stub...
channel.shutdown(); // close channel and stub

Problem appears when I'm using interceptors. Method ClientInterceptors.intercept(channel, interceptor) return Channel (not ChannelImpl) which hasn't any shutdown method.

ClientHeaderInterceptor<?> interceptor = interceptor();
Channel channel = ClientInterceptors.intercept(NettyChannelBuilder.<...>.build(), interceptor);
Service.ServiceStub stub = Service.newStub(channel);


...do some stuf with stub...
channel.shutdown(); // Error, Channel does not have shutdown method
stub.shutdown(); // Also error

In my opinion stubs (normal, blocking and sync) should have method shutdown() to close them. Right now there is no way to end program.

FYI in RouteClient (from gRPC-java tutorials) you are also using approach with cloasing ChannelImpl.

Regards

Martin

[Kun Zhang]

By design the Stub and the Channel are not tied to particular resources. They are just interfaces that makes RPCs. ChannelImpl, however, is tied to a particular transport (connection). That's why only ChannelImpl has shutdown().

As a ChannelImpl can be used under multiple Stubs or intercepting Channels, adding shutdown() to Stub or Channel would require reference-counting the ChannelImpl, and it's hard to do it right.

Here we follow the rule that who creates an object is responsible for cleaning it up. Since it's you that call NettyChannelBuilder.build() and creates the ChannelImpl, you should save the ChannelImpl instance shut it down as desired.

[Eric Anderson]

Issue 64 suggested the same thing a while back. I was against it as it seems at odds with the interceptor design. I just now updated the issue with some explanation of a few things I see going wrong with it.

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[Eric Anderson]

I just created issue 538 as an alternative. I'm not 100% sold on it either, but thought you might be interested.

[Martin Grześlowski]

It would be great to have this feature from #538. Sometimes i far easier to have only one Channel object (ChannelImpl) and just care about this.