I am currently doing development with GWT and Google Appengine. It appears that GWT hosted mode (debug) runs in the cache directory structure. It also copies the file out/exploded/project/WEB-INF/appengine-generated/local_db.bin to the cache directory to run. I do a lot of testing that I need to empty the datastore, which I do by deleting the for mentioned file. At first is seems to work fine, then it starts failing to delete the local_db.bin file in the cache directory. I have to go find the GWT running directory in the cache to make it work.
It seems to be a very bad design to make the running directory in the cache. For a long time it was a great mystery why I was getting magic reads of a non existent file. It is also really crappy that I have to go into the cache directory to clean up a run process. Can someone please explain why this is the case?