I used to think .gdk_lock was used by mserver the same way Linux daemons use lock files - the filesystem enforces serialization, so if you do:
1. if (lock file present) then locking failed 2. create the lock file 3. if (creation failed) then locking failed 4. locking successful
that's a valid non-blocking locking procedure.
However, it appears that:
* .gdk_lock is not always empty, and can have text such as
USR=12096163 PID=5844 TIME=Thu Nov 24 15:35:08 2016 @ LOGON USR=12096163 PID=5844 TIME=Thu Nov 24 15:42:26 2016 @ LOGOFF
* If .gdk_lock is not always created on DB startup, nor deleted on shutdown. * The locking using .gdk_lock is actually an flock() on its 5th byte (offset 4) and never any other one. * The GDKunlockhome() file will cause a second file descriptor opening in addition to GDKlockfile
So I'm a bit confused about the locking scheme. Help?
Eyal