[PATCH] D46621: [Support] call FlushFileBuffers when closing raw_fd_ostream on Windows

[Zachary Turner via llvm-commits]

This doesn’t seem necessary, as the problem in the referenced cl only
affects memory mapped files. Furthermore, this will probably adversely
impact performance.
On Tue, May 8, 2018 at 7:27 PM Bob Haarman via Phabricator <
reviews at reviews.llvm.org> wrote:

> inglorion created this revision.
> inglorion added reviewers: rnk, zturner.
> Herald added subscribers: hiraditya, mehdi_amini.
>
> We have observed a problem where files we write on Windows are
> sometimes read back with bytes having value 0, when that was not the
> value that was written. https://reviews.llvm.org/D42925 works around this
> problem for files we
> write to by memory-mapping them. This change applies a similar fix for
> files we write using raw_fd_ostream, as we do for archives and in the
> LTO cache.
>
>
> https://reviews.llvm.org/D46621
>
> Files:
>   llvm/lib/Support/raw_ostream.cpp
>
>
> Index: llvm/lib/Support/raw_ostream.cpp
> ===================================================================
> --- llvm/lib/Support/raw_ostream.cpp
> +++ llvm/lib/Support/raw_ostream.cpp
> @@ -551,6 +551,15 @@
>    if (FD >= 0) {
>      flush();
>      if (ShouldClose) {
> +#if defined(LLVM_ON_WIN32)
> +      // On Windows, we have observed that programs that read a file
> after it
> +      // was written will sometimes read bytes with value 0, when that
> isn't
> +      // actually the value that was written. Calling FlushFileBuffers
> before
> +      // closing the file seems to avoid the issue.
> +      HANDLE FileHandle = reinterpret_cast<HANDLE>(_get_osfhandle(FD));
> +      if (FileHandle != INVALID_HANDLE_VALUE)
> +        ::FlushFileBuffers(FileHandle);
> +#endif
>        if (auto EC = sys::Process::SafelyCloseFileDescriptor(FD))
>          error_detected(EC);
>      }
>
>
>
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