Am 09.09.2013 13:31, schrieb Sven Barth:
Am 08.09.2013 22:32, schrieb Tomas Hajny:
On Sun, September 8, 2013 19:32, Sven Barth wrote:
On 08.09.2013 14:17, Bart wrote:
On 9/8/13, Tomas Hajny <xhaj...@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.
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.
I believe that there are three different things:
1) We have a sequence in GetDir implementation for Windows targets which
changes the current directory. While this is obviously necessary due to
limitations of the respective Win32/64 API for retrieving current
directory combined with characteristics of the supported path names, it
may not be expected by the programmers who may have no call to
SetCurrentDirectory within their code and thus expect no issues with
thread safety. I don't know if it is possible to use a critical
section or
something like that to avoid switching to another thread during this
context, but it might be useful to think about it in my opinion.
On Windows this is completely useless. A process has only *one*
current directory. The current-directory-per-drive ones are only
implemented inside the command line interpreter and other programs
that use the crt library (not to be confused with the crt unit). So
the calling of SetCurrentDirectory inside ExpandFilename is not only
not threadsafe, but doesn't result in something useful either!
Correction, there seems to be a bit more magic going on... I'll report back.
Regards,
Sven
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