[PATCH] mingw: improve performance of mingw_unlink()

From: Jeff Hostetler <jeffhost@microsoft.com>

Update mingw_unlink() to first try to delete the file with existing permissions before trying to force it.

Windows throws an error when trying to delete a read-only file. The mingw_unlink() compatibility wrapper always tries to _wchmod(666) the file before calling _wunlink() to avoid that error. However, since most files in the worktree are already writable, this is usually wasted effort.

Update mingw_unlink() to just call DeleteFileW() directly and if that succeeds return. If that fails, fall back into the existing code path to update the permissions and use _wunlink() to get the existing error code mapping.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
    Windows: improve checkout performance with large numbers of files
    
    Jeff Hostetler contributed this patch to Git for Windows a while ago
    after measuring ~15% improvement
    [https://github.com/microsoft/git/pull/264#issuecomment-617216583] with
    a very, very large worktree:
    
    > I ran a series of timing tests on the Office repo on my Z440 desktop.
    > This was a full enlistment at HEAD. I ran git sparse-checkout disable 
    > to populate the entire worktree and then git sparse-checkout init
    > --cone to delete everything except the files at root. I repeated that
    > sequence 3 times.
    >
    > Each init needed to delete about 2.1M files.
    >
    > git sparse-checkout init
    >
    > old: 636.1s, 638.3s, 637.2s, 637.2s new: 535.9s, 544.8s, 533.3s,
    > 538.0s
    >
    > In this example, run time was decreased by 15%.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-704%2Fdscho%2Funlink-perf-gfw-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-704/dscho/unlink-perf-gfw-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/704

 compat/mingw.c | 3 +++
 1 file changed, 3 insertions(+)