Re: fcntl file locking and pthreads

[Mark Mielke]

On Sun, May 04, 2003 at 02:13:25AM -0400, Mikhail Kruk wrote:
> on 2.4 kernels fcntl-based file locking does not work with 
> clone-based threads as expected (by me): two threads of the same process 
> can acquire exclusive lock on a file at the same time.
> flock()-based locks work as expected, i.e. only one thread can have an 
> exclusive lock at a time.
> What would it take to make fcntl work as flock?

I don't think per-thread locks is entirely reasonable. The file descriptor
is shared between threads, which means that attributes (including locks)
attached to the file descriptor, are shared between threads.

I would suggest that system resources such as advisory locks be considered
per process, and inter-thread synchronization be performed using thread
synchronization primitives such as the mutex. Feel free to quote from POSIX
to tell me that this suggestion is wrong.

mark

-- 
[e-mail]/[e-mail]/[e-mail] __________________________
.  .  _  ._  . .   .__    .  . ._. .__ .   . . .__  | Neighbourhood Coder
|\/| |_| |_| |/    |_     |\/|  |  |_  |   |/  |_   | 
|  | | | | \ | \   |__ .  |  | .|. |__ |__ | \ |__  | Ottawa, Ontario, Canada

  One ring to rule them all, one ring to find them, one ring to bring them all
                       and in the darkness bind them...

                           http://mark.mielke.cc/