@Override
    public void sendMessage(O message) {
        pendingMessagesUpdater.incrementAndGet(this);
        if (ctx.eventLoop().inEventLoop()) {
            doSendMessage(message);
        } else {
            ctx.eventLoop().execute(() -> doSendMessage(message));
        }
    }
Encapsulates the state of a single server call, reading messages from the client, passing to business logic
via {@link ServerCall.Listener}, and writing messages passed back to the response.
grpc/src/main/java/com/linecorp/armeria/server/grpc/StreamingServerCall.java