korry wrote: > > The Win32 API for locking seems mighty strange to me. > > Linux/Unix byte locking is advisory (meaning that one lock can block > another lock, but it can't block a read).
No -- it is advisory meaning that a process that does not try to acquire the lock is not locked out. You can certainly block a file in exclusive mode, using the LOCK_EX flag. (And at least on my Linux system, there is mandatory locking too, using the fcntl() interface). I think the next question is -- how would the lock interface be used? We could acquire an exclusive lock on postmaster start (to make sure no backend is running), then reduce it to a shared lock. Every backend would inherit the shared lock. But the lock exchange is not guaranteed to be atomic so a new postmaster could start just after we acquire the lock and acquire the shared lock. It'd need to be complemented with another lock. > Win32 locking is mandatory (at least in the most portable form) so a > lock blocks a reader. There is also shared/exclusive locking of a file on Win32. My comment weas more directed at the fact that you have to "create some sort of lock handle" from a file handle and then lock the lock handle, or something like that. I don't recall the exact details but it was strange (as opposed to just open and then flock). -- Alvaro Herrera http://www.CommandPrompt.com/ The PostgreSQL Company - Command Prompt, Inc. ---------------------------(end of broadcast)--------------------------- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
