De la: Guru Shetty [mailto:g...@ovn.org] Trimis: Friday, July 15, 2016 5:49 AM Către: Alin Serdean <aserd...@cloudbasesolutions.com> Cc: Paul Boca <pb...@cloudbasesolutions.com>; dev@openvswitch.org Subiect: Re: [ovs-dev] [PATCH V7] windows: Added lockf function and lock PID file
On 14 July 2016 at 19:25, Alin Serdean <aserd...@cloudbasesolutions.com<mailto:aserd...@cloudbasesolutions.com>> wrote: [Alin Gabriel Serdean: ] https://msdn.microsoft.com/en-us/library/windows/desktop/aa365203(v=vs.85).aspx The part: "If the same range is locked with an exclusive and a shared lock, two unlock operations are necessary to unlock the region; the first unlock operation unlocks the exclusive lock, the second unlock operation unlocks the shared lock." I see. Thank you. (I am blind!). I wonder whether we actually need the exclusive lock then? If what we need is just shared lock, why not just take it in the beginning? Would it have been possible to open the file in write mode if someone had taken the exclusive lock in the first place? [Alin Gabriel Serdean: ] No worries the MS documentation is not that easy to follow or precise in certain scenarios ☺. The problem is “Locking a portion of a file for shared access denies all processes write access to the specified region of the file, including the process that first locks the region. All processes can read the locked region.” “Locking a portion of a file for exclusive access denies all other processes both read and write access to the specified region of the file. Locking a region that goes beyond the current end-of-file position is not an error.” I agree it doesn’t make any sense why a shared lock would block the owner but probably they had reasons to implement it that way. What I was trying to say was, we open the file in write mode. It wouldn't have been successful if someone else had taken a lock (exclusive or shared). Am I correct? If so, why take exclusive lock again to write? Just write the pid and then take shared lock. Would that cause problems? (I must be missing some subtlety here.) [Alin Gabriel Serdean: ] If we just open the file in write mode and write the pid and then take the shared lock, someone else could write in the file between the moment we opened it and gained the shared lock. _______________________________________________ dev mailing list dev@openvswitch.org http://openvswitch.org/mailman/listinfo/dev
