I am trying to develop an ATM cash transaction monitoring application.
I am using the CEN-XFS APIs to listen to events generated by the Cash Dispenser Device Class (CWA1574-8) interface. I read through the WFS_CMD_CDM_DISPENSE command documentation and I find that none of the events that this command generates clearly signifies that a cash transaction has failed due to cash jam.
Will WFS_EXEE_CDM_CASHUNITERROR be generated when a cash jam happens? There is another event WFS_EXEE_CDM_NOTEERROR which says it will be generated on an item detection error, so it is clearly not anything about cash jam.
Similarly, one more question related to this is that "items taken" is indicated by WFS_SRVE_CDM_ITEMSTAKEN event, so, I can listen to that event, but "items not taken" has no event and it is returned as error code "WFS_ERR_CDM_ITEMSNOTTAKEN". My program is only a monitoring application and my program listens to these events, how do I now know that customer has not taken the presented cash? Looks like a poor design.
Like #SuperG280 said this is really not possible without modifying the main application. CEN XFS is not really made for observers in mind.
So if you want to create an all purpose monitoring application then the only way is to create shallow XFS Manager for the main application to use. It can simply wrap the real XFS Manager and just provide all command completion events to your monitoring application as well as the main application.
I know that some devices from certain manufacturer do provide configuration settings that can be used to create a situation where that device will post all command execution completing events to all listeners.
This though is restricting support for certain ATM manufacturers and to only those devices that has this setting provided.
Related
We have a situation where several of our services are shared across our system. For example one that tracks stock movements. Whenever the stock level of an article changes an event is raised.
The problem we run in to is that while sometimes another service may be interested in ALL stock change events (for example to do some aggregation), in most cases only stock changes that are the result of a specific action are interesting.
The problem we now face is this. Say have an IArticleStockChangedEvent event that contains the article number, the stock change and a ProcessId that requested the change. This event is raised for every change in the article stock.
Now some external service has a saga to change 10 articles and commands the stock service to make it so. It also implements IHandleMessages to keep track of the progress. This works well in theory, but in practise this means that the service containing this saga will be flooded with unrelated IArticleStockChangedEvent message for which it will be unable to find a corresponding saga instance. While not technically breaking anything it causes unnecessary delays in the system.
I'm not really looking forward to creating a new kind of IArticleStockChangedEvent for every saga that can possibly cause a stock change. What is the recommended approach to handle this issue?
Thanks
The knowledge about which IArticleStockChangedEvent events you need to be delivered to your service lives inside your "external" service and changes dynamically, so it's not possible (or is complex and non-scalable) to make a filter in either Stock service or at a transport level (Ex. Service Bus subscription filter).
To make an optimization, namely avoid deserialization of the IArticleStockChangedEvent, you might consider custom Behavior<IIncomingPhysicalMessageContext> where you read the Stock item's Id from message header and lookup db to see if there is any saga for that stock item and if not, short circuit the message processing.
Better solution might be to use Reply and reply with a message from Stock service.
I have built a simple PCI driver for reading and writing data to a PCI device. I have also added interrupt support, so when there is a PCI interrupt an ISR is called. This all seems to work.
I would like to inform an external application of the interrupt. So far I haven't found a suitable mechanism. The interrupt could come at any time, and is dependent on Sensors connected to the PCI device.
I have found the following:-
1 Event objects which can be passed to the KMDF driver via read, write, iocontrol commands (Overlapped object)
2 Plug and Play notifications, which can be use used by (Toaster example code) the driver to inform the app of PNP events.
A notification method would be ideal, however it doesn't look like one exists for my particular use case.
There are at least 2 ways to achieve what you are looking for
Inverted call model - send IOCTL(s) to the driver which the driver will keep pending and will complete them as and when it needs to notify the user mode about the occurrence of the event that it is interested in. You can read more about this approach here.
Use shared event handles. A user mode application communicates the event handle(s) to kernel mode using an IOCTL. The kernel mode increments the reference count to ensure that the handle remains valid when it needs to use it and then signals the event when necessary. You can read more about this approach here.
The first approach is more preferred for various reasons that you will find while reading the linked articles. If your use case requires the kernel mode to not only indicate the occurrence of an event but also send some data back to user mode then the second approach is not suitable for your requirement and you should focus on the first approach alone.
We've created a web application that is an a e-book reader. So one thing to keep in mind is that the domain is not exactly that of reading a physical book. We are now trying to gather users' reading behavior by storing information about e-book pages accessed by our users. Since this information goes to a data warehouse we thought raising an event from the bookcontroller is the right way to do it.
bus.Publish()
But we are not sure if it should be a publish or a send since there is really only one consumer to this event and that is our business intelligence team. We've also read that it is not advisable to publish from the web app (http://www.make-awesome.com/2010/10/why-not-publish-nservicebus-messages-from-a-web-application/). So now the alternative is to use bus.Send(RecordPageAccessedCommand)
But the above command does not change our application state in anyway. So is it truly a command? I have a feeling that the mistake we are making is using NServiebus's features (Publish,Send) and trying to equate it with what a command or event is.
Please let me know what the solution to this is.
Based on the information you provided, I would recommend "sending" to your endpoint.
Sending a command implies that the endpoint handling the message should do something. In your case, recording that the page was accessed is the thing the endpoint should do.
Publishing an event implies that you are notifying 0..n subscribers that something occurred. You could publish an event from your command handler if some other service in your system was interested in the fact that a page was accessed. The key point here is that it's not a "fact" until you've recorded it.
I've found that consumers tend to grow once data is available. Having the ability to publish an event from your command handler will make it trivial to notify new consumers without changing/risking your existing code base.
The RecordPageAccessedCommand is a command as it is commanding the system to do something, in this case, record that a page has been accessed.
If I've understood your scenario correctly. A message should be sent from your controller to the "Business intelligence Team Service" telling the system to record that a page has been accessed. This service would store this information and would be the owner/technical authority of this information.
No other services should store or require this information in its pure form, they can however subscribe to events from this service, in highly contrived scenario for example, when a user reads 1000 pages the "Business intelligence Team Service" can publish an event that a 1000 pages have been read ie Bus.Publish(), which may be handled by a billing service that gives a discount for the user on their next purchase.
The data warehouse can have access to this information stored in your "Business intelligence Team Service" as it would fall under IT/OPS.
I've got a JMS messaging system implemented with two queues. One is used as a standard queue second is an error queue.
This system was implemented to handle database concurrency in my application. Basically, there are users and users have assets. One user can interact with another user and as a result of this interaction their assets can change. One user can interact with single user at once, so they cannot start another interaction before the first one finishes. However, one user can be in interaction with other users multiple times [as long as they started the interaction].
What I did was: crated an "interaction registry" in redis, where I store the ID of users who begin an interaction. During interaction I gather all changes that should be made to the second user's assets, and after interaction is finished I send those changes to the queue [user who has started the interaction is saved within the original transaction]. After the interaction is finished I clear the ID from registry in redis.
Listener of my queue will receive a message with information about changes to the user that need to be done. Listener will get all objects which require a change from the database and update it. Listener will check before each update if there is an interaction started by the user being updated. If there is - listener will rollback the transaction and put the message back on the queue. However, if there's something else wrong, message will be put on to the error queue and will be retried several times before it is logged and marked as failed. Phew.
Now I'm at the point where I need to create a proper integration test, so that I make sure no future changes will screw this up.
Positive testing is easy, unfortunately I have to test scenarios, where during updates there's an OptimisticLockFailureException, my own UserInteractingException & some other exceptions [catch (Exception e) that is].
I can simulate my UserInteractingException by creating a payload with hundreds of objects to be updated by the listener and changing one of it in the test. Same thing with OptimisticLockFailureException. But I have no idea how to simulate something else [I can't even think of what could it be].
Also, this testing scenario based on a fluke [well, chance that presented scenario will not trigger an error is very low] is not something I like. I would like to have something more concrete.
Is there any other, good, way to test this scenarios?
Thanks
I did as I described in the original question and it seems to work fine.
Any delays I can test with camel.
I have a WF4 Service with a flowchart as the root activity. It contains multiple correlated receive activites and decision branching to step through an approval process. The receive activities work perfectly until I try and use one as the trigger for a pick branch.
I am running tracking so can see that the receive is opened and in the persistance I can see the associated bookmark. When I send a client message with the receive type it does not trigger. I have a delay pick branch that fires OK but then the subsequent receive also does not work.
I have checked these receive activities individually and they work OK when not used as the pick trigger. I have tried the pick within a Sequence and a While but no difference.
I cannot see any difference between my implementation and may examples on the web. Am I missing something extra required when the receive is encapsulated by a pick branch?
There is nothing special about a PickBranch trigger that would cause a receive to behave differently so I suspect it is something with the Receive itself. What kind of errors are you seeing at the client application?