Why it's so hard to understand? [LWN.net]

Why it's so hard to understand?

Posted May 27, 2010 7:28 UTC (Thu) by khim (subscriber, #9252)
In reply to: The road forward for systemd by Tobu
Parent article: The road forward for systemd

I've had this discussion so many times and I still can't believe people are thinking like that. Guys, OR and XOR are different operations! Please open the logic textbook and read about difference between them! This is vital if you want to talk about systemd!

Either implicit dependencies are used, and you rely on socket activation, but you don't start daemons as early as they could be

This perfect illustration: systemd can do A or B, ok, but since if you do A (but don't do B) you need to do this and if you do B (but not do A) you need to do that - and you so are doing neither this nor that so how can that work? Of course in reality systemd can do "A (activate service via socket) or B (start services from the list) and that means it can do A and B simultaneously! Terrific, uber-uncomprehensible idea, isn't it? Implicit dependencies are used and you start daemons as early as possible (i.e.: you start all daemons in parallel). If daemon A needs deamon B it does not mean daemon B should be started earlier - it means daemon A will start first and then will wait for daemon B activation. This will start the system in fastest time possible.

It's all explained in original paper. I know, I know, majority of population can not even imagine OR operation and only think about XOR (they call it OR, of course) - but these people shouldn't discuss design of systemd, that's all.

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Why it's so hard to understand?

Posted May 29, 2010 0:25 UTC (Sat) by baldridgeec (guest, #55283) [Link]

I've had this discussion so many times and I still can't believe people are thinking like that. Guys, OR and XOR are different operations! Please open the logic textbook and read about difference between them! This is vital if you want to talk about systemd!
Either implicit dependencies are used, and you rely on socket activation, but you don't start daemons as early as they could be

I haven't done enough thought experiments or study of the init process limitations to have any kind of coherent input about systemd's particulars (despite having read Lennart's blog post with interest last week), but I do have a rather decent knowledge of linguistics in general, and English in particular.

"Either" is a word which introduces a parameter to the conditional expressed by "or." It is a flag which notifies the reader that the first and second clauses of the conditional are mutually exclusive.

In other words:

("OR" != "XOR") == 1

but also

("XOR" == "Either..or") == 1

Why it's so hard to understand?

Posted Jun 4, 2010 23:37 UTC (Fri) by Wol (guest, #4433) [Link]

"Either" (in normal English usage) does *not* imply the two sides of the "or" are exclusive.

"You can borrow my car if you do either A or B" - in other words I don't care which you do and you could do both if you wish. "either" is a filler word which implies "xor" but doesn't require it. If you *really* mean XOR, you have to say "either but not both".

Cheers,
Wol

Why it's so hard to understand?

Posted May 29, 2010 0:30 UTC (Sat) by baldridgeec (guest, #55283) [Link]

I just re-read your post and I think I misunderstood it the first time.

Sorry for the pedantic tone in my previous comment! I guess I get a thrill from taking the wind out of grammar Nazis' sails when they're wrong, but you were addressing a different concern (and you're correct, as far as I understand the process.)