I figured out a somewhat silly, but highly effective way do progress reporting. The basic idea is that we know the output file names and the exact order in which they will appear. Therefore if output X+1 exists on the file system it means that output X is already complete. Now the worker thread polls the file system waiting for the output files to appear and then processses them instead of waiting until the forked subprocess terminates. In basic testing it appears that this mechanism is about the same speed as the previous version that does not include progress reporting. This implementation is cross platform and doesn't suffer from the problems of inotify (Linux only) or kqueues (BSD/Mac OS equivalent of inotify that requires an open file descriptor for each monitored file). I still need to implement input option parsing and a decompress mode so I can do proper testing.
Adding my initial PCA work. This project depends on packJPG. I see intermittent issues and I'm not sure if it is caused by my code or by the packJPG code.