Avoid concurrence when text_io.fopen

Question

Hi, i open a file
     in_file := Text_IO.Fopen(filename, 'r');
only to read the data and do some inserts.
But I need to know nobody is opening the file, and show a message if it's happening. How?
If i do after the open:
     if Text_IO.is_open(in_file) then
     --message alert....
          end if;
it shows it always, because the file handler is of the file open... In fact, is_open is only the know if the file you've opened remains opened...
...but not for to know if it's already opened by somebody else (what I would want)
Thanks!

Answer 1

If the operating system (OS) tells you that the file is already opened for read-only, then you need to see how the OS informs you. If the OS does not inform you (most do not), then you won't know.
There are work arounds if the OS doesn't tell you. You can create an OS script that you use to open the file. When the script runs, it creates a text file indicating the file is open. Create another script to delete the text file when closing the file. Then your form checks to see if the text file exists before opening the file. If the text file exists, then you know the file was already opened.
Also, some OS will prevent opening a second file if the first file is opened for writing.