I want to send two WSMs, one on regular intervals to enable a vehicle (V1) receive the information about vehicle behind them (V2) from the vehicle (V3), which is behind V2.
The second WSM is only sent out in certain cases (as a warning message) and as soon as vehicles receive the warning WSM, I want them to change the lane.
Question is: how can I implement two WSM actions independent from each other? Can I at all use multiple WSMs for this purpose or shall I define a new message type for it?
Related
My team is considering if we can use mass transit as a primary solution for sagas in RabbitMq (vs NServiceBus). I admit that our experience which solution like masstransit and nserviceBus are minimal and we have started to introduce messaging into our system. So I sorry if my question will be simple or even stupid.
However, when I reviewed the mass transit documentation I noticed that I am not sure if that is possible to solve one of our cases.
The case looks like:
One of our components will produce up to 100 messages which will be "sent" to queue. These messages are a result of a single operation in a system. All of the messages will have the same Correlated Id and our internal publication id (same too).
1) is it possible to define a single instance saga (by correlated id) which will wait until it receives all messages from a queue and then process them as a single batch?
2) otherwise, is there any solution to ensure all of the sent messages was processed? (Consistency batch?) I assume that correlated Id will serve as a way to found an existing saga instance (singleton). In the ideal case, I would like to complete an instance of a saga When the system will process every message which belongs to a single group (to one publication)
I look at CompositeEvent too but I do not sure if I could use it to "ensure" that every message was processed and then I would let to complete saga for specific correlated Id.
Can you explain how could it be achieved? And into what mechanism I should look at in order to correlated id a lot of messages with the same id to the single saga and then complete if all of msg will be consumed?
Thank you in advance for any response
What you describe is how correlation by id works. It is like that out of the box.
So, in short - when you configure correlation for your messages correctly, all messages with the same correlation id will be handled by the same saga instance.
Concerning the second question - unless you publish a separate event that would inform the saga about how messages it should expect, how would it know that? You can definitely schedule a long timeout, attempting and assuming that within the timeout all the messages will be received by the saga, but it's not reliable.
Composite events won't help here since they are for messages with different types to be handled as one when all of them arrive and it doesn't count for the number of messages of each type. It just waits for one message of each type.
The ability to receive a series of messages and then operate on them in a batch is a common case, so much so that there is a sample showing how to do just that:
Batch Sample
Each saga instance has a unique correlation identifier, and as long as those messages can be correlated to that single instance, MassTransit will manage the concurrency (either optimistic or pessimistic, and depending upon the saga storage engine).
I'd suggest reviewing the state machine in the sample, and seeing how that compares to your scenario.
I am implementing an example of spring-boot and axon. I have two events
(deposit and withdraw account balance). I want to know is there any way to get the state of the Account Aggregate by a given date ?
I want to get not just the final state, but to replay events in a range of dates.
I think I can help with this.
In the context of Axon Framework, you can start a replay of events by telling a given TrackingEventProcessor to 'reset' it's Tokens. By the way, the current description on this in the Reference Guide can be found here.
These TrackingTokens are the objects which know how far a given TrackingEventProcessor is in terms of handling events from the Event Stream. Thus resetting/adjusting these TrackingTokens is what will issue a Replay of events.
Knowing all these, the second step is to look at the methods the TrackingEventProcessor provides to 'reset tokens', which is threefold:
TrackingEventProcessor#resetTokens()
TrackingEventProcessor#resetTokens(Function<StreamableMessageSource, TrackingToken>)
TrackingEventProcessor#resetTokens(TrackingToken)
Option one will reset your tokens to the beginning of the event stream, which will thus replay everything.
Option two and three however give you the opportunity to provide a TrackingToken.
Thus, you could provide a TrackingToken starting from several points on the Event Stream. So, how do you go about to creating such a TrackingToken at a specific point in time? To that end, you should take a look at the StreamableMessageSource interface, which has the following operations:
StreamableMessageSource#createTailToken()
StreamableMessageSource#createHeadToken()
StreamableMessageSource#createTokenAt(Instant)
StreamableMessageSource#createTokenSince(Duration)
Option 1 is what's used to create a token at the start of the stream, whilst 2 will create a token at the head of the stream.
Option 3 and 4 will however allow you to create a token at a specific point in time, thus allowing you to replay all the events since the defined instance up to now.
There is one caveat in this scenario however. You're asking to replay an Aggregate. From Axon's perspective by default the Aggregate is the Command Model in a CQRS set up, thus dealing with Commands going in to your system. In the majority of the applications, you want Commands (e.g. the requests to change something) to occur on the current state of the application. As such, the Repository provided to retrieve an Aggregate does not allow specifying a point in time.
The above described solution in regards to replaying is thus solely tied to Query Model creation, as the TrackingEventProcessor is part of the Event Handling side in your application most often used to create views. This idea also ties in with your questions, that you want to know the "state of the Account Aggregate" at a given point in time. That's not a command, but a query, as you have 'a request for data' instead of 'the request to change state'.
Hope this helps you out #Safe!
I have three rsu in my app. is there any id for rsu like car id for cars? if yes, how can I get rsu id in rsu initializer method? if not how can I distinguish between rsus?
If you the consider the demo scenario, it has one RSU integrated stored in an Array structure. However, you can have an arbitrary number of RSUs by increasing the number in the brackets.
Therefore, you can address every RSU individually by its module id *.rsu[<index>] (e.g. RSUExampleScenario.rsu[0]) which is also available in the code via getId(). OMNeT++ also provides other useful functions for getting the name of a module.
If this is identifier is not enough for you, at least in the Mac layer there is an additional id which you can use to distinguish nodes.
If this is not not enough, you would need to add your own identifier variable to the NED module.
I need to send a message only to one vehicle that i want to choose. I am reading the available TraCIDemo11p and the cars are broadcasting the message to all cars. How can change that and make it send the message to only one care for example to car number 3.Thank you
Keep in mind that communication between cars in Veins (or any MANET simulator) is wireless which means that many cars can hear the MAC frame that sent to a specific node.
To send a message from car A to another car B, they must be in their wireless range or they support an ad-hoc routing protocol to reach other not-in-range cars (which is not implemented in Veins, AFAIK).
If you are sure that both sending and receiving cars are in range, then you can fill the destination address in WSM by the ID of the intended car and let the WAVE application to delete any message that has a destination address different from the local ID.
I am a PhD student at INSA Lyon, France. I work on mobility in urban environments.
I installed Omnet ++ 4.6, Sumo 0.21.0 and Veins 3.0 to simulate vehicle mobility.
In fact, I've never used Omnet ++ in my previous work. I read the existing tutorials of Omnet ++ in the website and now I want to start to simulate these two small scenarios:
1 Scenario: I want to have a set of mobile vehicles that exchange information among themselves
2nd scenario: I want to have a set of mobile vehicles and a set of fixed RSU that exchange information
What can I change in the existing example of Veins to lead simulate these scenarios please?
Can you help me to do this please.
Thanks very much in advance.
If you are interested in using Road Side Units (RSUs) in your simulation, you might want to base your work on Veins 4a2 instead. Its example simulation already includes an RSU participating in data exchange: as soon as a vehicle stops, it sends a message. Each vehicle and RSU that receives a message re-broadcasts one message per simulation. Each vehicle that receives a message computes a different route to avoid the road where the message originated. See this answer for a screenshot of the resulting simulation.