[fpc-pascal] DoDirSeparators and special filenames on Windows

[Mattias Gaertner]

On Sun, 08 Sep 2013 19:32:23 +0200
Sven Barth <pascaldragon at googlemail.com> wrote:

> On 08.09.2013 14:17, Bart wrote:
> > 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)?
>[...]
> > 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.
> 
> The problem is not GetCurrentDirectory itself (this function and 
> SetCurrentDirectory use the process's PEB lock to access the current 
> directory which is stored inside the PEB as well), but that different 
> threads could call SetCurrentDirectory with different values and thus a 
> thread who expected the current directory to be a specific one might 
> resolve a relative path (by using another WinAPI function) using a 
> current directory set by a different thread.
> 
> So this can not be solved by using a lock inside ExpandFilename and 
> might happen on other systems as well as long as the current directory 
> is not stored per thread.

Actually the problem is that Windows has multiple current directories,
but you can only read the one of the active drive.

For example:
Thread 1: ExpandFilename('C:test.pas');
Thread 2: ExpandFilename('B:test.pas');

In order to get the current directory of C: (B:) you have to switch the
current drive and switch back.

Mattias