FileMeasureProgressCallback

This callback type is used by g_file_measure_disk_usage() to make periodic progress reports when measuring the amount of disk spaced used by a directory.

These calls are made on a best-effort basis and not all types of #GFile will support them. At the minimum, however, one call will always be made immediately.

In the case that there is no support, @reporting will be set to false (and the other values undefined) and no further calls will be made. Otherwise, the @reporting will be true and the other values all-zeros during the first (immediate) call. In this way, you can know which type of progress UI to show without a delay.

For g_file_measure_disk_usage() the callback is made directly. For g_file_measure_disk_usage_async() the callback is made via the default main context of the calling thread (ie: the same way that the final async result would be reported).