The importance of measuring performance changes is a topic that has been covered by others smarter and more experienced than me, but I have a recent simple tale.

I’ve simplified the code quite a bit in order to demonstrate the issue. Suppose I have a wrapper around an image (it has many more attributes):

   1: class Picture

   2: {

   3:     Image _image;

   4:     string _path;

   5: 

   6:     public Image Photo

   7:     {

   8:         get

   9:         {

  10:             if (_image==null && !string.IsNullOrEmpty(_path))

  11:             {

  12:                 _image = Bitmap.FromFile(_path);

  13:             }

  14:             return _image;

  15:         }

  16:     }

  17: 

  18: }

I had this and a view that loading about 2,700 of these into a customized ListView control at program startup. On a cold start (where none of the pictures were in the disk’s cache), it would take 27 seconds. Unacceptable.

What to do?

My first thought was to load the pictures asynchronously. I wrapped Bitmap.FromFile() into a function and called it asynchronously. When it was done, it fired an event that percolated up to the top.

Well, I spent about 30 minutes implementing that and ran it–horrible. The list showed up immediately, but it was unusable. The problem? Dumping 2,700 items into the ThreadPool queue is a problem. It doesn’t create 2,700 threads, but it causes enough problems to not be a viable option.

Asynchronicity is still the answer, though. But it’s at a different level. Instead of loading the individual images asynchronously, I skipped loading the images when creating the list control and instead launched a thread to load all the images and update them when done. The list loads in under a second, and the pictures show up little by little after that.

Measure, measure, measure. And pay attention.

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