Please increase the interval of thumbnail generation for very large files. This would apply for example for files over 10M. This would be a default value one should be able to change via Preferences. Implementation can be an integer representing MB. If this is implementation wise connected to the automated refresh if the view of the image, please also increase that interval.
Fixing this will save CPU resources when geeqie is generating thumbnails for large files while these files are being written to disk by another program. For example downloads from the Internet of applications like GIMP or ImageMagick that are writing several large files at the same time.
Refreshing the view with hotkey 'R' will force regeneration of thumbnails for large files when they have been changed. But while these files are being written to disk, the thumbnail generation should be slowed down until the file has been written completely. Typically an interval of 15 seconds would suffice. Even this could be offered as an settings which can be altered by the user via Preferences.