Question

This seems to be an easy task, I just don’t know which way to start using OmniThreadLibrary:

I create a Task that does some processing in the background. The results are stored in fields of the task class and are continuously filled with new values.

Now the main thread wants to read these fields and display their values from time to time.
Therefore it needs to access these fields and make sure that they are not written to at these moments (Synchronize).

How can this be done with OmniThreadLibrary?

Answer 1

There’s no direct support for owner/thread data sharing in the OTL, because all my multithreaded experience tells me that this is always a bad thing to do. (Agree, sometimes it is the only solution but still it’s a bad thing.)

You should go with the second mghie’s suggestion – create an (optionally interface-based) object and pass this object (or its interface) to the thread. Something like this:

sharedData := TSharedData.Create;
task := CreateTask(worker).SetParameter('shared', sharedData).Run;

worker:

sharedData := Task.Param['shared'].AsObject as TSharedData;

Another way to solve the problem would be to send a ‘please send update’ message to the task whenever the user presses the UpdateNow button. That task would then respond with an object containing current state. However, if the task performs a lengthy uninterruptable calculation this solution is not really appropriate and the shared state approach works better.