User:Zero Linden/Office Hours/2007 Sep 06

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Transcript of Zero Linden's office hours:

[8:12] Zha Ewry: Hark. Zero. A cafeinated Zero.
[8:12] Saijanai Kuhn: sure, but if Apple could use an optimized pipelines for games programming, it would free up resources for other things. Assuming that that would fix the problem, of course
[8:12] Saijanai Kuhn: WELL-caffinated, one asumes
[8:12] Zero Linden: yes - cafeinated, and finally logged-in!
[8:13] Tedd Maa: OS X is still BSD based, these things take time
[8:13] Tedd Maa: going from BSD to a fully fledged multimedia OS is no small task
[8:13] Zero Linden: ya know, 18 months ago - every blip in operations caused most of us in dev to get involved
[8:13] Saijanai Kuhn: OS X is likely always going to be FreeBSD based. The former chieft-tech officer helped design BSD IIRC
[8:13] Zero Linden: now - there are so many people, that it isn't useful for us all to jump on it
[8:13] Zero Linden: so - ops folks were on it and all I did was watch from the sidelines
[8:14] Saijanai Kuhn: this sounds like a drastic improvement, at least for your home life
[8:14] Tedd Maa: BSD in its pure form is useless for videos/high end games
[8:14] Saijanai Kuhn: I'm pretty sure that Avie helped redesign it at least somewhat to target that market
[8:15] Saijanai Kuhn: at least you're not ruthed this time, Aha
[8:15] Saijanai Kuhn: Zha
[8:15] Zha Ewry: Sigh.
[8:15] Tedd Maa: ping
[8:15] Zero Linden: pong?
[8:16] Tedd Maa: hurray :)
[8:16] Zero Linden: well- alas, I've got to go at 8:30 - waaaay busy day
[8:16] Zha Ewry: So... Quick question zero.. Just becausde I'm curious.
[8:16] Saijanai Kuhn: Zero, I've been playing with teh GUI classes. I think you're slightly wrong about the xml being too closely tied to the client, but there's sure some NASTY dependencies in the classes themselves
[8:16] Zha Ewry: When I see (Hippos) as an active friend, (and no others) which part of the process had flaked out?
[8:17] Zero Linden: hehe - (Hippos)
[8:17] Tedd Maa: well, it beats Nullsofts Lama fetish
[8:18] Zero Linden: that's what I get for trying to be cute
[8:18] Saijanai Kuhn: someone pointed to me this HUGE thread about hippos. 600+ messages
[8:18] Zero Linden: control-shift-alt-H = hippos!
[8:18] Zero Linden: small easter egg in code base
[8:18] Zero Linden: but control-shift-H = Go Home
[8:18] Zero Linden: don't slipp
[8:18] Zha Ewry: Oh my.
[8:18] Zha Ewry: yes, it does.
[8:18] Zero Linden: so (Hippos) as a name isn't actually a failure
[8:19] Saijanai Kuhn: htat's hippocritical, ZEro
[8:19] Zero Linden: Regions deal with avatar ids, which are 128bit UUIDs
[8:19] Zha Ewry: Well, presumbably, it's some placeholder or another.
[8:19] Zero Linden: the mapping of a UUID to a name is a database lookup
[8:19] Saijanai Kuhn: actually, what I read says there's a 1% chance of it happening at random as a joke
[8:19] Zero Linden: so there is a name cache object in the sim (actually, same class is in the viewer)
[8:19] Zero Linden: that lets other code do something like this:
[8:20] Zero Linden: gNameCache.getName(someID, callback);
[8:20] Zero Linden: wehre the callback is like foundName(agentId, firstname, lastname)
[8:20] Zero Linden: so what happens is, something wants the name
[8:21] Zero Linden: and the name cache doesn't have it, so it calls the call back immediatly with "(waiting)"
[8:21] Zha Ewry: Right, which we also see.
[8:21] Zero Linden: and then later calls it with "Amy Beta"
[8:21] Zha Ewry: From time to time you see (waiting) as a friend
[8:21] Zero Linden: the "(hippos)" version is just a random replacement for "(waiting)" for amusement only
[8:21] Zero Linden: just a string swap
[8:21] Zero Linden: NOW
[8:21] Zero Linden: for debatebale reasons
[8:21] Tedd Maa: FYI its possible to run viewer over terminal server if you start SL before you log on
[8:22] Zero Linden: the name cache offers another API
[8:22] Zha Ewry: Soemtimes, often I get (hipppos) and (waiting) back to back and no live friends.
[8:22] Zero Linden: gNameCache.getName(agnetId, &firstName, &lastName)
[8:22] Zero Linden: see the problem with that? There is no way to update the caller
[8:22] Zha Ewry: Right.
[8:22] Zha Ewry: So.. if iti isn't in the cache, you DOA, if you use that call
[8:23] Zero Linden: Alas, this an impedence mis-match with imperative languages and network programming
[8:23] Zha Ewry: unless you inspect the result, and retry yourself, and all. (Which implied you know the strings which repreent bad result.. which.. ick)
[8:23] Zero Linden: one assumes you can always deliver the correct answer right now, the other assumes you might get around to it at some point
[8:24] Zero Linden: This forces application programs to constantly code in a sort of continuation passing style (the callback) in a language that doesn't really support it too well
[8:24] Zero Linden: (C++)
[8:24] Zero Linden: Zha - fortuently noone (that I know) inspects the strings
[8:24] Zha Ewry: Right.. And.. that's pervasive in the code, it seems, which probably is unavaoidable
[8:24] Zero Linden: if they use the "short cut" call, they get what they ask for - a non-updating answer
[8:25] Zero Linden: The whole thing is annoying - since think of all the places in the viewer you want to display a name
[8:25] Zero Linden: everyone of those has to code this kind of continuation style
[8:25] Zero Linden: and then you have to deal with - well, here's the call back, but, er, what if the user closes the thing displaying the name before the answer comes back?
[8:26] Zero Linden: so, it also begs for weak pointers
[8:26] Zha Ewry: Does the immediate response give you a return indicating if it found a name?
[8:26] Tedd Maa: event hooks then
[8:26] Zha Ewry: Event hooks are just another form of continuatoin.. the same issue, of what happens, if the reason for the callback went away, obtains.
[8:26] Zero Linden: no, Zha
[8:27] Zha Ewry: Ah. So you can't even say "Got it, I don't need the continuation.." sigh.
[8:27] Zero Linden: Tedd - the problem with event hooks is that then you must create an event for every possible callback and they all must go through the same system - and usually type
[8:27] Zero Linden: so it is a global design bottle neck
[8:27] Tedd Maa: yes, but less code - hook up, place request - if object goes away hook is removed (with GC or on obj dispose) and reply ignored
[8:28] Zha Ewry: Messier framework code, tho.
[8:28] Zero Linden: not to mention, then you have to do some form of event registration or you're distributiong too many around
[8:28] Tedd Maa: breaks your standard code, but it works...
[8:28] Saijanai Kuhn: this is SL. Framework mess worries? er...
[8:28] Zha Ewry: Since.. you now have to manage the creation and destruction under threadsafe locks, and all.
[8:29] Zero Linden: at which point, Tedd, it is about the same as registering and unregistering the callback
[8:29] Zero Linden: which the name cache supports
[8:30] Zha Ewry: So, will you be in SF, on Thursday next?
[8:30] Zha Ewry: (Err, that was aimed at Zero)
[8:30] Zero Linden: In much of the HTTP code we use this sort of paradigm: create an instance of a subclass of a HTTPResponder and hand it
[8:30] Tedd Maa: as so often, no easy way around it .. point is time, you can't execute sequenced code but skip through commands that use time
[8:31] Zero Linden: to the HTTP client class for making some request. When the answer comes back from the server, invoke a result() method on the object
[8:31] Zero Linden: or an error() method if something goes wrong
[8:31] Tedd Maa: Im about to implement HTTP object in OpenSim LSL engine
[8:31] Tedd Maa: fun programming
[8:31] Zero Linden: that instance generally keeps ref-counted pointers to the things it needs. If something changes while the request is out so that we don't need the info any more
[8:32] Zero Linden: we just set a state bool in the reponder instance so that when it gets it's result() or fail() it just returns
[8:32] Zero Linden: Yes
[8:32] Zero Linden: So, Zha, yes - I'll be in SF next Thursday, and there will be no office hours
[8:32] Zero Linden: here
[8:33] Zha Ewry: Well, I'll cheat, and see you there, then
[8:33] Zero Linden: the rest of you - keep an eye on the wiki
[8:33] Saijanai Kuhn cries. But my Zero fix. What about my zero fix?
[8:33] Squirrel Wood: POKE!!!!
[8:34] Zero Linden: starting next Thursday I'm going to be talking in much greater detail about coming architectural changes in the next year
[8:34] Zha Ewry: Heh. I went cold turkey for two weeks while on Vacation.
[8:34] Squirrel Wood: I need your vote on :p
[8:34] Zero Linden: in fact, LL is going to solicit lots of input from the community on it
[8:34] Saijanai Kuhn needs to start reading up on server architecture. Actually, needs to finish reading that INTRO to servers he's got inn a box someplace
[8:34] Zero Linden: This will all be of a very techinical nature - not picking UI features
[8:34] Squirrel Wood: /ao on
[8:35] Zero Linden: more like - here are 100 different protocols in the system, help us revamp them for going over web services
[8:35] Tedd Maa: "Modern Operating Systems" is a good book to read
[8:35] Zha Ewry: Much more peverse stuff, such as the proper nature of annotating REST based servcie endpoints :-)
[8:35] Tedd Maa: one of the best I've read
[8:35] Saijanai Kuhn: OK. Who is it by?
[8:35] Squirrel Wood: 100 protocols... reduce them to one ^^
[8:35] Tedd Maa: Tanenbaum
[8:35] Saijanai Kuhn: Think I have that one. Xenix, right?
[8:35] Zero Linden: Squirrel -there are about 400~500 messages in the Second Life system
[8:36] Tedd Maa: it goes over common hardware/OS+some exotic in great detail
[8:36] Zero Linden: the comprise somewhere between 200 to 300 functions the system performs.... each of which can be thought of as a protocol -- in the pure sense
[8:36] Zero Linden: you might perfer to think of them as APIs
[8:36] Zero Linden: or as functions
[8:36] Zero Linden: but really all the same thing
[8:36] Zha Ewry: Contracts?
[8:36] Saijanai Kuhn: I'm still hunting for the code that handles llSetText 's hover text.
[8:36] Zha Ewry: Yeah, all the same in the end.
[8:36] Squirrel Wood: Oy
[8:36] Zero Linden: That too
[8:37] Zero Linden: SL is complex, no doubt, and rich in functions
[8:37] Squirrel Wood: wrap them into one protocol where the header tells what kind of "decoder" is needed for the payload data
[8:37] Saijanai Kuhn: and rich it compexity too
[8:37] Saijanai Kuhn: rich in*
[8:37] Zero Linden: Squirrel
[8:37] Zero Linden: yes, the bottom layers of the protocol stack will be shared
[8:37] Zero Linden: from bottom to top:
[8:37] Squirrel Wood: :)
[8:38] Zero Linden: IP - TCP - HTTP - LLSD
[8:38] Zha Ewry: But. the real meat is in the contract that happens as you unwrap that next level up.
[8:38] Zero Linden: so now we just need to design the URL endpoints (one per function, probably) and the LLSD payloads of both the request and the response
[8:38] Zero Linden: for about 200 to 300 features
[8:38] Saijanai Kuhn: will the revision be able to handle "peer2peer" communciations as well on the client side?
[8:38] Zero Linden: and then we're done
[8:38] Zha Ewry: LOL
[8:38] Zero Linden: well.... except for the implementation part
[8:39] Zero Linden: No, the new architecture doesn't really handle peer to peeer at all--
[8:39] Zha Ewry: and desctribe the idempotency of each call, the lifecylcle of all the resources, the relationship between modified versions of resources.
[8:39] Squirrel Wood: beer-2-beer... ^^
[8:39] Saijanai Kuhn: a long-term need though, I think
[8:39] Zero Linden: since most users are on asymetric network connections: both upload is lower, and due to firewalls and NAT, you can't connect in
[8:40] Squirrel Wood: What about torrent ?
[8:40] Saijanai Kuhn: Private sandboxes, collaborative computation, etc...
[8:40] Zero Linden: The later being the biggest problem
[8:40] Zero Linden: well, torrent requires that savvy users modify their firewalls
[8:40] Zero Linden: and, well, my mother can't do that!
[8:40] Zha Ewry: Chuckle.
[8:40] Zero Linden: Nor can many corporate users
[8:41] Zero Linden: Nor should most home users
[8:41] Saijanai Kuhn is still working on hosting a test apache server that can communciate with SL from his mac
[8:41] Zero Linden: (lemme just open up this fireall thingy on my cabel modem box..... Port? I dunno - just all of 'em I guess..... )
[8:41] Tedd Maa: well, there is a hole in the firewalls and routers
[8:41] Tedd Maa: UDP
[8:41] Saijanai Kuhn: firewall + NAT. Only recently learned what NAT meant
[8:41] Squirrel Wood: Well, I for once cannot connect to SL at all from work because SL doesn't honor proxy settings defined in IE for example.
[8:41] Tedd Maa: you can specify source/destination port and hence establish a session with ayone
[8:42] Zero Linden: Tedd, not usually, UDP only works in if you speak out on it in most routers
[8:42] Tedd Maa: as long as you can negotiate th eports first
[8:42] Zero Linden: and even then it is dicey - believe me, weh know!
[8:42] Tedd Maa: both speak out the first time, as long as ports match the session is established
[8:42] Tedd Maa: then both can communicate
[8:42] Squirrel Wood: got a router and firewall here. both are still using the out-of-the-box settings. torrents work flawlessly.
[8:42] Zha Ewry: Sometimes..
[8:42] Zero Linden: Tedd, yes, there are tricks that VOIP uses ... but having read the technical details, I'm not fond of the idea of implementing such
[8:43] Zero Linden: and really, we don't have a big use case for peer to peer right now
[8:43] Saijanai Kuhn: the voice server stuff took a while to get right
[8:43] Tedd Maa: no, not advocating that .. ;)
[8:43] Zero Linden: for example, there is little that peer to peer would do to enahcne this experience we are sharing
[8:43] Zha Ewry: peer to peer, in a deep sense, also has interesting state melding issues
[8:43] Squirrel Wood: UDP is often blocked entirely in company networks
[8:43] Saijanai Kuhn: for most users, absolutely
[8:43] Tedd Maa: just saying, UDP CAN be used to overcome router/firewall problems
[8:43] Saijanai Kuhn: but some scientific users might find the collaborative computation of value
[8:43] Zero Linden: Well, firends - sorry due to SL borkage today's was short - but I've already got to go
[8:43] Tedd Maa: I have written a prototype app and testet it, it works
[8:43] Saijanai Kuhn: and I still want to play in my private sandbox with a few friends
[8:44] Zha Ewry: Glad you made it at all.
[8:44] Saijanai Kuhn: thanks very much for coming, Zero
[8:44] Zero Linden: I'll be here Tuesday....
[8:44] Zha Ewry: Saijanai.. you may still be better off putting up a private sim,
[8:44] Zero Linden: till then
[8:44] Zha Ewry: then doing that peer to peer
[8:44] Tedd Maa: bye