On Wed, 22 Feb 2006, Pat Martin wrote:
> I had actually looked at that site, but when I do the commands
>
> testfile = open('testlock', 'a+')
> fcntl.flock(mboxfile.fileno(), fcntl.LOCK_EX)
>
> in the interpreter and then try to access the file in another terminal
> (I leave the interpreter open) I can write to the file just fine with
> vi. So I am not thinking it is working. Unless I am missing something...
Hi Pat,
Oh! Ok, what's happening is that the code places an "advisory" lock.
Any other program that tries to get a lock will wait as expected. But a
noncooperating program that doesn't look at locks won't care.
It's possible that 'vi' is not cooperating: it may not be doing an flock()
call. There is a line item in the vim TODO documentation about this:
"""
8 Add file locking. Lock a file when starting to edit it with flock()
or fcntl(). This patch has advisory file locking while
reading/writing the file: ~/vim/patches/kahn_file_locking.
"""
(http://www.vim.org/htmldoc/todo.html)
For more information on this situation, see:
http://en.wikipedia.org/wiki/File_locking
You might be able to put wrappers to force a common access point to the
file you're trying to lock; an example of this approach is in the 'visudo'
program that tries to provide exclusive access to /etc/sudoers.
I have to admit that I don't know much more about this or how people work
around exclusive access to files; does anyone else on the Tutor list have
suggestions?
Good luck to you!
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