Provide blocking versions of Bitmap.Load*

[reactiveui]

Provide blocking versions of Bitmap.Load*

[anaisbetts]

Also reading through the iOS code, I was curious why the work to load the image was being dispatched to the main thread.

Good question, might have to do some history digging

[bordoley]

Ps. I realize this would be a breaking API change, so probably 2.0 only.

[anaisbetts]

The main rationale is that if the code you are executing is already on a background thread or eventloop(wink) where you can block the thread safely, the cost of the context switch to the threadpool outweights the benefit of being async.

So the problem is, that on WinRT and WP8, you must dispatch to the UI thread to load images, it has to be async. However, I think these are two separate problems - something can be async but not necessarily always do a Task.Run. If someone were to contribute a cross-platform API called "IsOnUIThread" 😉, it would be trivial to implement bitmap loading s.t. it wouldn't always jump threads

[bordoley]

I'm not a fan of "IsOnUIThread" flag changing the behavior of a library call. Particularly for code that could block, I think the decision of whether a call should be async or not really needs to be explicitly decided by the caller based upon their performance criteria. For instance to play devils advocate to my use case, there may be scenarios where code running on a second event loop actually cannot block and the caller would prefer the use of the task pool and thread hop vs blocking the thread. A concrete example of this is a WPF app where different windows in the app have their own threads with their own dispatchers.