Long Operation Status

Question

When performing a long operation in your application, how do you promote information from your business tier to your UI?

Events? Passing in a status object which is hooked to the UI?

Before I start I just wondered what cunning ways you guys and girls have come up with.

Answer 1

You should make a difference between: this can be done in a GUI-app and this needs to be done in batch.

Something that runs for 5 minutes: in your gui-app or in batch?

Answer 2

If we consider a typical Web app - one that is not using a push technology such as COMET, updated information will be fetched by the browser intermittely, perhaps when the user requests, perhaps when an AJAX background call is made.

In that scenario I have my service offering a Status operation.

 int requestSomeWork( ... data ... ) ; // returns an id

 Status getStatus( int id );  // tell me about a previously submitted request

This style is useful not only for displaying progress information but also in recovery from failure scenarios. I may provide additional methods so that we can determine what happened if the Browser or Server crashes just as we were creating a request

 int[] findRequest( ... search Criteria ... );  // I think I submitted a request like ... what's its id?

If we have a "live" UI, either thick client or COMET then we can add event processing

 void registerForUpdates( id, callMe );

Answer 3

This seems exactly what events are designed for. Letting other objects know about changes to that object.

Having an ProgressUpdated event that reports a progress percentage or something along lines is how I would do it.

Answer 4

There are two ways I usually do this:

1. Pushing data with events. Quite simply, the long method knows how much it's done and whenever it finishes a piece it raises an event and pushes data to the UI.
2. Polling. Suppose the method is for reading a file. It will always update a property somewhere with its progress, and the UI will poll that property once every 100-200ms to update the progress. The reason for 100-200ms is that lower than that the user won't notice and it will only slow down the operation; higher and the progress would be 'clunky'.