Maperitive running scripts

For the last week or so I’ve been busting my fingers with one of the harder things to implement in a desktop GUI: application responsiveness when executing longer-running tasks. By longer-running I mean something that takes more than a couple of seconds.

Simple desktop applications tend to run everything synchronously: when the user presses a button, the action gets run. After the action finishes, the control is given back to the user. Simple, but totally crappy. The problem is that the action gets run on the same thread that services the GUI, so until the action finishes, the application will not be able even to refresh itself or respond in any meaningful way to user clicks or key presses. And since there is no refresh, you cannot show any progress indicators to the user. I know I wouldn’t want to wait half an hour for something to finish without some reassurance that the application is still alive and not waiting for the electricity to run out.

Maperitive already had a lot of responsiveness code implemented, but it was still an “under the construction” design. The additional complication was the fact I want Maperitive to have a good script runner and scripts can take a very long time (downloading OSM data, generating tiles etc.). After a lot of trials and errors I finally managed to implement the whole thing in a consistent package. And believe me when I say it was not easy.

So what is new:

  • When running scripts (or longer tasks), Maperitive draws an indicator on the map (see the screenshot above) and launches a “sort of modal” mode – most of GUI controls are disabled so the script doesn’t get confused by some inadvertent user action. However, the application is still responsive: you can view the progress of the script in the command log.
  • Aborting scripts: as the indicator says, you can press the escape key to abort the script. If you prefer torturing your mouse instead of your keyboard, there’s an “Abort task” button in the bottom right corner which does the same thing.

Not all of running tasks have been switched to the new system. Loading OSM files is one example of a task that will still block the GUI, but I will gradually improve these things.

You can download the latest release at http://maperitive.net/download/

Enjoy!