Comment 5 for bug 842676

Two options:

(a) If we release the GIL, and call pkgAllUpgrade(), pkgAllUpgrade() can modify the depCache. If now another (Python)-thread accesses the depcache, we're lost (and that's potentially a real bug, given that APT is almost totally not thread-safe).

(b) The cache file is broken - we rule out too short cache files now, as that is detected since August 2011, so it can basically only be caused by a broken storage or memory.