The current implementation of rename uses ReplaceFile if the
destination file already exists. According to the documentation for
ReplaceFile, the source file is opened without a sharing mode. This
means that there is a short interval of time between when ReplaceFile
renames the file and when it closes the file during which the
destination file cannot be opened.
This behaviour is not POSIX compliant because rename is supposed
to be atomic. It was also causing intermittent link failures when
linking with a ThinLTO cache; the ThinLTO cache implementation expects
all cache files to be openable.
This patch addresses that problem by re-implementing rename
using CreateFile and SetFileInformationByHandle. It is roughly a
reimplementation of ReplaceFile with a better sharing policy as well
as support for renaming in the case where the destination file does
not exist.
This implementation is still not fully POSIX. Specifically in the case
where the destination file is open at the point when rename is called,
there will be a short interval of time during which the destination
file will not exist. It isn't clear whether it is possible to avoid
this using the Windows API.
Differential Revision: https://reviews.llvm.org/D38570
llvm-svn: 315079
On Windows, fs::rename() could fail is another process was reading the
file at the same time using fs::openFileForRead(). In most cases the user
wouldn't notice as fs::rename() will continue to retry for 2000ms. Typically
this is enough for the read to complete and a retry to succeed, but if the
disk is being it too hard then the response time might be longer than the
retry time and the rename would fail with a permission error.
Add FILE_SHARE_DELETE to the sharing flags for CreateFileW() in
fs::openFileForRead() and try ReplaceFileW() prior to MoveFileExW()
in fs::rename().
Based on an initial patch by Edd Dawson!
Differential Revision: http://reviews.llvm.org/D13647
llvm-svn: 250046
