[fpc-pascal] DoDirSeparators and special filenames on Windows

[Bart]

On 9/8/13, Tomas Hajny <XHajT03 at hajny.biz> wrote:

> Why do you believe that ExpandFilename is not threadsafe (on Windows or
> any other platform)?
..
> The only platform specific part inside
> ExpandFilename is a call to GetDir function retrieving the current
> directory. If that is not 'threadsafe' by itself (on Windows), then your
> statement is correct,

And that is exactly the point.
GetDir calls GetCurentDirectory and MS says (see:
http://msdn.microsoft.com/en-us/library/windows/desktop/aa364934%28v=vs.85%29.aspx)
that multithreaded applications should not call GetCurrentDirectory.

 > that some other thread may change the current directory during execution
> of ExpandFilename - well, that may be the case, but that is not special
> for Windows and it should be the responsibility of the programmer either
> not to change the current directory in other threads,

But GetDir just does that: it changes the current directory if it
tries to find the current directory on a drive that is not the current
drive.
It then calls SetCurrentDirectory with only the drive letter, and
calls GetCurrentDirectory again.

Why would I forbid my users to specify relative paths?
How would you feel if, as Jürgen suggests we prepend anything with
\\?\, you now cannot do a simple:
C:\Devel\Foo>fpc bar.pas -Fu..\MyLib
But you must do
C:\Devel\Foo>fpc C:\Devel\foo\bar.pas -FuC:\Devel\MyLib, because the
compiler is mutithreaded (this may be untrue, but just for the sake of
the argument), so expanding the filename is unsafe?

For the record: I am not stating that this (handling '\\?\') _must_ be
"fixed" in fpc, I am perfectly happy with "you should handle that on
the users side", which would mean NOT calling DoDirSeparators (and any
function that uses that) on such a filename.
It would be nice however if a "formal" point of view from the fpc core
team was given on this subject.

Bart