Open Com port failed (multi threading)

[Droopy]

Hi,

I wrote a C# program that is calling C++ legacy code to open a serial port
(using CreateFile (comPort,
GENERIC_READ|GENERIC_WRITE,0,NULL,OPEN_EXISTING,FI LE_FLAG_OVERLAPPED,NULL))
..
So far, it works.
Now, at startup, I start 4 C# threads.
These threads are opening Com ports #2, #3, #4 and #5.
Sometimes, these 4 Com ports are opened successfully but, most of the time,
1 Com port opening failed.
The GetLastError returns 5 (access denied).

So, my question is :

Is it safe to call 4 CreateFile (for different Com ports of course) in
parallel thread at the same time ?

Thanks in advance for your help,

Droopy.