On Tue, Jun 12, 2018 at 11:51 AM Edward Thomson <ethomson@xxxxxxxxxxxxxxxxx> wrote: > > On Tue, Jun 12, 2018 at 09:13:54AM +0300, Orgad Shaneh wrote: > > Some of my colleagues use an ancient version of Source Insight, which also > > locks files for write. > > If that application is locking files for writing (that is to say, it did > not specify the `FILE_SHARE_WRITE` bit in the sharing modes during > `CreateFile`) then this patch would not help. > > Applications, generally speaking, should be locking files for write. > It's the default in Win32 and .NET's file open APIs because few > applications are prepared to detect and support a file changing out from > underneath them in the middle of a read. I agree. > > It's less important than it was before those fixes, but it is still needed > > for users of Qt Creator 4.6 (previous versions just avoided mmap, 4.7 uses > > mmap only for system headers). Other tools on Windows might as well > > misbehave. > > I don't understand what mmap'ing via `CreateFileMapping` has to do with > this. It takes an existing `HANDLE` that was opened with `CreateFile`, > which is where the sharing mode was supplied. I'm not completely sure. The file is opened using CreateFile[1] with FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE. Then this handle is passed to CreateFileMapping[2]. For a reason I don't understand, when mapping is used, the handle is never released (until the file is closed), but when it is not used, the file is being read, then the handle is released. Maybe Ivan or Nikolai can shed some light on this process. Anyway, with Qt Creator 4.7 this should be a non-issue, so I'm reluctant about this change here. > I would be surprised if there are other tools on Windows that have > specified `FILE_SHARE_WRITE` but not `FILE_SHARE_DELETE`. Generally > speaking, if you don't care about another process changing a file > underneath you then you should specify both. If you do then you should > specify neither. The problem is that even if you specify FILE_SHARE_WRITE and FILE_SHARE_DELETE, the file can be unlinked, but it cannot be created with the same name until its handle is closed, unless you rename it *before* unlinking. - Orgad [1] https://github.com/llvm-mirror/llvm/blob/371257e/lib/Support/Windows/Path.inc#L1045 [2] https://github.com/llvm-mirror/llvm/blob/371257e/lib/Support/Windows/Path.inc#L836
