I have an NFS file system mounted on many machines. I am attempting to use file locking to get exclusive access by one system to a file. The critical code section shown here: 

        # loop through file names looking for one we can lock
        open ( my $file_handle, '+<', $file_name ) or next;
        if ( !flock( $file_handle, LOCK_EX | LOCK_NB ) ) {
            close( $file_handle );
            next;
        }
        # do some work here based on the file contents
        unlink $file_name;
        close( $file_handle );

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This almost always works, but occasionally there is a failure where two machines get a lock on the same file. It appears there is a race between unlinking (deleting) the file and releasing the lock. It seems like there is a small window where the lock is actually released before the file is deleted allowing another machine to lock and read the file before it is deleted.

I am wondering if this is a known problem and if there is a preferred way to work around this.

In reply to NFS File Locking by jbw8387

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