Thanks Alastair. Mark Allan’s email set me off reading things in that area, and I am indeed reading the man page for setiopolicy_np at this very moment!
Certainly sounds like the API I am looking for although, as you say, it’s not clear where the “default” policy fits into the hierarchy. The man page states that [IOPOL_IMPORTANT] "is the default I/O policy for new threads”, and so if true then that would suggest that all a program can do is DOWNgrade its priority. However, the man page is evidently not entirely correct, based on the result you got, so who knows! I also wonder what priority the Finder would use for copying a folder. I might hope it would set itself to STANDARD or THROTTLE; if it does do that, then that would suggest that even this is not proving enough to prevent my code getting backlogged… On 5 Jul 2016, at 16:34, Alastair Houghton <alast...@alastairs-place.net> wrote: > On 5 Jul 2016, at 13:36, Jonathan Taylor <jonathan.tay...@glasgow.ac.uk> > wrote: >> >> This is a long shot, but I thought I would ask in case an API exists to do >> what I want. One of the roles of my code is to record video to disk as it is >> received from a camera. A magnetic hard disk can normally keep up with this, >> but if the user is also doing other things on the computer (e.g. long file >> copy in the Finder) then we are unable to keep up, and accumulate an >> ever-increasing backlog of frames waiting to be saved. This eventually leads >> to running out of memory, thrashing, and an unresponsive computer. Dropping >> frames is not an option. In this case, the computer is a dedicated >> workstation running my code, so it *is* correct for me to consider my code >> to be the number 1 priority on the computer. >> >> What I am wondering is whether there is some way I can communicate this >> requirement, to cause other apps such as the finder to get disk access at >> lower priority. Or alternatively, a way that I can demand high priority >> temporarily, at times when I identify that we have accumulated a save >> backlog? > > Take a look at get/setiopolicy_np(). It isn’t clear from the documentation > exactly what the default behaviour is; when I tried calling getiopolicy_np() > I got IOPOL_DEFAULT, which isn’t even mentioned as a value on the man page, > but you may find that setting your thread/process’s IO policy to > IOPOL_IMPORTANT solves your problem. _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
