Don't forget the classic

Don't forget the classic

Posted Dec 6, 2007 22:55 UTC (Thu) by vmole (guest, #111)
In reply to: Don't forget the classic by nix
Parent article: Book review: Linux System Programming

I wish SysVIPC had never existed, ick.

Ick? Ick? If "ick" satisfactorily expresses your opinion of SysV IPC, then you clearly haven't suffered enough :-). I *could* use the words that come into my mind, but then Corbett would have to delete this comment.

For those who haven't had the pleasure, among the problems is that the namespace is completely independent of the normal Unix namespace (files), and there's no way to programatically query it. Also, the associated resources were limited, and they didn't automatically close when all the programs using one exited uncleanly (like file descriptors do). And by "limited" I mean on the order of 16 or 32. System wide. Also, while you could list the in-use resource (ipcs), there was pretty much no way to find out who had created or was using a particular id. Imagine the fun.

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There's more fun. While SysV message queues can fill up because, well, 
they're full (they have a bounded maximum size), they can also fill up 
because *other* queues have filled up to the point where the system won't 
allow any more messages into any queues. Most Unixes have ridiculously low 
limits (64 messages or 64Kb across all queues is not unusual) so it is 
utterly trivial to produce horrible deadlocks with this system.

(Of course they don't work with select(). That would be *useful*.)

(I would have used stronger language than `ick', too, but I didn't want to 
get the bills for setting a thousand people's computers on fire.)