outlook add-in, slowing down outlook UI

Question

I have written an outlook add-in to filter spam. The issue is that when the add-in is doing its job of processing a message, and especially with a large attachment that it is procesing / reading through, it is taking a lot of time and because of this the main outlook UI is un-responsive and users cannot do anything with the UI.

Is there an asynchrounous way of running the add-in processing, so that the outlook UI remains OK.

The add-in does a lot of things dueing its procesing of each message and hence it takes a lot of time.

Answer 1

It's just like with any other program basically. If you need to do something outside of the main thread do so (i.e. create another thread). There's no Outlook-specific API or framework, though.

You have to be extra careful about exception handling though. Unhandled exceptions escaping from a thread can have the weirdest results (though in most cases Outlook will simply crash).

Also, if at all possible you should try to avoid or at least drastically limit accessing the Outlook Object Model from within your processing thread.

Finally, another thing you should make sure of is that you explicitly call CoInitializeEx / CoUninitialize specially for your new thread if it in any way directly or indirectly uses COM-related functions.

Answer 2

Creating another thread won't help you if the bulk of the time is being spent in the Outlook API. Due to the threading model in Outlook, accessing the object model from another thread will cause the call to be marshalled to the main thread which means now your UI is still frozen and your background thread is blocking.

If most of the work is spent doing things that don't touch the Outlook object model, you'll probably see a significant improvement spinning off a separate worker thread (or thread pool) to process the attachments you've saved.