User:Zero Linden/Office Hours/2007 Sep 06

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 https://jira.secondlife.com/browse/MISC-632 :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