On Wed, Oct 23, 2024 at 05:04:58PM +0200, Patrick Steinhardt wrote: > Unless told otherwise, Windows will keep other processes from reading, > writing and deleting files when one has an open handle that was created > via `CreateFileW()`. This behaviour can be altered via `FILE_SHARE_*` > flags such that other processes _can_ read and/or modify such a file. > This sharing mechanism is quite important in the context of Git, as we > assume POSIX semantics all over the place. > > There are two calls where we don't set up those flags though: > > - We don't set `FILE_SHARE_DELETE` when creating a file for appending > via `mingw_open_append()`. This makes it impossible to delete the > file from another process or to replace it via an atomic rename. > > - When opening a file such that we can change its access/modification > times. This makes it impossible to perform any kind of operation > on this file at all from another process. While we only open the > file for a short amount of time to update its timestamps, this still > opens us up for a race condition with another process. > > Adapt both of these callsites to pass all three sharing flags. Interesting, and especially so noting that we *do* call CreateFileW() with the FILE_SHARE_DELETE flag in other functions like create_watch(), mingw_open_existing(), mingw_getcwd(), etc. Why didn't we call CreateFileW() with FILE_SHARE_DELETE in the below two functions? I assume Johannes Schindelin and/or Johannes Sixt (both CC'd) would know the answer. Regardless, it would be interesting and useful (IMHO) to include such a detail in the commit message. Thanks, Taylor
