void rename(in char[] from, in char[] to);
        Rename file from to to. If the target file exists, it is overwritten.

        Throws:
        FileException on error.

Just wanted to know if this operation is atomic?
or does it depend on the underlying file system?

In short, in the file nanoseconds/milliseconds that this operation is occurring is it possible for someone else to be reading the same file and get a dirty read (i.e. with only half of the contents overriden, etc)?

Thanks

On Thursday, 12 December 2013 at 17:08:13 UTC, Jacek Furmankiewicz wrote:
>    void rename(in char[] from, in char[] to);
>         Rename file from to to. If the target file exists, it is overwritten.
>
>         Throws:
>         FileException on error.
>
> Just wanted to know if this operation is atomic?
> or does it depend on the underlying file system?
>
> In short, in the file nanoseconds/milliseconds that this operation is occurring is it possible for someone else to be reading the same file and get a dirty read (i.e. with only half of the contents overriden, etc)?
>
> Thanks

Here's the implementation,as you can see it's just c function calls, no work is done in D:

void rename(in char[] from, in char[] to)
{
    version(Windows)
    {
        enforce(MoveFileExW(std.utf.toUTF16z(from), std.utf.toUTF16z(to), MOVEFILE_REPLACE_EXISTING),
                new FileException(
                    text("Attempting to rename file ", from, " to ",
                            to)));
    }
    else version(Posix)
        cenforce(core.stdc.stdio.rename(toStringz(from), toStringz(to)) == 0, to);
}


On a posix compliant system, I'm pretty sure this is guaranteed to be atomic as far as any other process is concerned. On windows, I don't know. A quick google suggests that there may have been a C or filesystem bug on OSX with regards to this.

Am Thu, 12 Dec 2013 18:08:12 +0100
schrieb "Jacek Furmankiewicz" <jacek99@gmail.com>:

>     void rename(in char[] from, in char[] to);
>          Rename file from to to. If the target file exists, it is
> overwritten.
> 
>          Throws:
>          FileException on error.
> 
> Just wanted to know if this operation is atomic?
> or does it depend on the underlying file system?
> 
> In short, in the file nanoseconds/milliseconds that this operation is occurring is it possible for someone else to be reading the same file and get a dirty read (i.e. with only half of the contents overriden, etc)?
> 
> Thanks

I don't know for sure, but it is likely you are on the safe side I guess ;)

1. the reading process probably didn't allow shared writing to
   the target file anyways (on Windows)
2. moving a file on the same file system is just a metadata
   update (giving the data a different name).
3. If all else fails, the target file is most likely deleted
   first, then recreated with the contents of the file to move
   which easily avoids what you describe.

You could try MoveFileEx on an opened target file with all sharing options enabled and see what happens.

-- 
Marco