private void closeChannel(final Endpoint endpoint) {
        final ManagedChannel ch = removeChannel(endpoint);
        LOG.info("Close connection: {}, {}.", endpoint, ch);
        if (ch != null) {
            ManagedChannelHelper.shutdownAndAwaitTermination(ch);
        }
    }
GRPC RPC client implement.

@author nicholas.jxf
@author jiachun.fjc
jraft-extension/rpc-grpc-impl/src/main/java/com/alipay/sofa/jraft/rpc/impl/GrpcClient.java