Re: [PATCH] checkout files in-place

From: Edward Thomson <ethomson@edwardthomson.com>
Date: Jun 11, 2018, 20:35 UTC
Message-ID: <20180611203541.GA6@606faba9ba17>
In-Reply-To: <20180610194444.GA1913@Sonnenschein.localdomain>

On Sun, Jun 10, 2018 at 09:44:45PM +0200, Clemens Buchacher wrote:

Show 5 quoted lines

> 
> It is safe to do this on Linux file systems, even if open file handles
> still exist, because unlink only removes the directory reference to the
> file. On Windows, however, a file cannot be deleted until all handles to
> it are closed. If a file cannot be deleted, its name cannot be reused.

I'm nervous about this proposed change, since it feels like it's addressing an issue that only exists in QT Creator.

You've accurately described the default semantics in Win32. A file cannot be deleted until all handles to it are closed, unless it was opened with `FILE_SHARE_DELETE` as their sharing mode. This is not the default sharing mode in either Win32 or .NET.

However, for your patch to have an effect, all processes with a handle open must have specified `FILE_SHARE_WRITE`. This is rather uncommon, since it's also not included in the default Win32 or .NET sharing mode. This is because it's uncommon that you would want other processes to change the data underneath you in between ReadFile() calls.

So your patch will benefit people who have processes that have `FILE_SHARE_WRITE` set but not `FILE_SHARE_DELETE` set, which I think is generally an uncommon scenario to want to support.

Generally if you're willing to accept files changing underneath you, then you probably want to allow them to be deleted, too. So this feels like something that's very specific to QT Creator. Or are there other IDEs or development tools that use these open semantics that I'm not aware of?

Cheers- -ed