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SubjectRe: fcntl file locking and pthreads
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

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