I like the Event Aggregator but run into the situation where I subscribe to and publish the same same message. This potentially makes the code run twice. I thought I could make an easy extension method to unsubscribe from the message, publish, and then subscribe to the message.
Is this possible or is there a better pattern (maybe use a GUID for each message to ignore handling a message you sent)?
An idea is to pass the sender in the message and ensure to have received it in a different instance before performing the action.
Related
I am considering using deferred messages as a delay/timeout alerting mechanism within my Saga. I would do this by sending a deferred message at the same time as sending a message to a handler to do some time-consuming work.
If that handler fails to publish a response within the deferred timespan the Saga is alerted to the timeout/delay via the deferred message arrival. This is different to a handler failure as its still running, just slower than expected.
The issue comes if everything runs as expected, its possible that the Saga will complete all of its steps and you'd find many deferred messages waiting to be delivered to a Saga that no longer exists. Is there a way to clean up the deferred messages you know are no longer required?
Perhaps there is a nicer way of implementing this functionality in Rebus?
Once sent, deferred messages cannot be cancelled.
But Rebus happens to ignore messages that cannot be correlated with a saga instance, and the saga handler does not allow for that particular message type to initiate a new saga, so if the saga instance is gone, the message will simply be swallowed.
That's the difference between using IHandleMessages<CanBeIgnored> and IAmInitiatedBy<CannotBeIgnored> on your saga. 🙂
In below scenario, what would be the bahavior of Axon -
Command Bus recieved the command
It creates an event
However messaging infra is down (say kafka)
Does Axon has re-queing capability for event or any other alternative to handle this scenario.
If you're using Axon, you know it differentiates between Command, Event and Query messages. I'd suggest to be specific in your question which message type you want to retry.
However, I am going to make the assumption it's about events, as your stating Kafka.
If this is the case, I'd highly recommend reading the reference guide on the matter, as it states how you can uncouple Kafka publication from actual event storage in Axon.
Simply put, use a TrackingEventProcessor as the means to publish events on Kafka, as this will ensure a dedicate thread is used for publication instead of the same thread storing the event. Added, the TrackingEventProcessor can be replayed, thus "re-process" events.
I have a situation where I need to wait for response from device(using mqtt broker which doesnt matter in current questions context).
Whenever I get an API call on one specific endpoint
I need to wait(2-5 seconds depending upon the need) for response from device on the other handler(mqtt handler => https://github.com/gausby/tortoise)
this handler needs to notify me somehow I got this msg(if handler received msg withing that time) for the particular device id
if device matches and controller action method get notified we send back success response otherwise we send failure response
Any msg received before or after wait time doesnt matter(just consider it unsubscribed)
I am not really sure about whats the best way to achieve above requirement. any help is welcome, thanks
spawn() a process for the first handler. In the first handler, spawn() another process for the second handler passing self() as one of the arguments. Then enter a receive clause with a 2-5 second timeout specified in the after clause. Have the second handler send() a message to the first handler with the data that the second handler acquires.
If the receive in the first handler times out, then do whatever you want to do in the after clause, if the receive reads a message before it times out, then do whatever you need to do with the data.
Then, if you let the process running the first handler die, then you won't have to worry about junk messages in its mailbox.
Sorry for my English. I use RocketChat/meteor-streamer in my app. On readme page, in downsides section written that "Since the library don't keep track of data, you will not receive lost data while offline after reconnection. But we have an event to notify you on reconnections passing the latest record received so you can call a method to verify and get the missing data." What method or event I must to call, to keep track data state? Thanks.
There appears to be a function onReconnect for registering handlers for that event.
I'm using a separate class and unique method for sending mail.All my web pages, will call the method to send the mail. But, I'm using Client.SendAsync() to send the mail. The following error occurs while sending the mail asynchronously.
"Asynchronous operations are not allowed in this context. Page starting an asynchronous operation has to have the Async attribute set to true and an asynchronous operation can only be started on a page prior to PreRenderComplete event"
I set Async=true in #page directive, but, as I'm using separate class, so no use of it. Is there any other way to overcome this problem?
Seems you just need to start your async task before PreRenderComplete event; do you mind to post some relevant ASP.NET code?
Also, read this: Running an asynchronous operation triggered by an ASP.NET web page request
This article may be of some help to you:
Fire and Forget Email, Webservices and More in ASP.NET
Setting Async to true is OK if that separated class is declared, instantiated and within the context of the page request.
However you probably need to handle SendCompleted event.
See the sample codes in this MSDN Reference.