The Next Mainstream Programming Language: A Game Developer's Perspective :: Redux

[Sean Kelly]

Sean Cavanaugh wrote:
> Reposting, as I didn't have my name show up properly due to outlook express 
> configuration fun, and any threaded readers are going to camoflauge my 
> response to a nearly year old post :)
> 
> 
> "Marcio" <mqmnews123 at sglebs.com> wrote in message
> news:ecipfc$15v4$1 at digitaldaemon.com...
>> http://www.cs.princeton.edu/~dpw/popl/06/Tim-POPL.ppt
> 
> 
> I'm new here but this somewhat old thread starting with this .ppt is very
> interesting to me since I work with the UE3 engine as a middleware.  Its
> pretty much dead on, as far as what the future is going to be, and that is
> in a massively parallel/threaded environment.  Those that do not make the
> transition are going to have very noticably 'rigid' game simulations that
> are far less capable.  Only the problem from my point of view is there isn't
> a single good language make the leap with.  Sure you can have a truely
> expert programmer get your threading right with the current tools available,
> but the reality is the current tools and languages available to make
> threaded programs are pretty bad.  In addition you end up with only 'one
> guy' who is responsible for far too much code since he has to wrangle
> everyone elses broken stuff into shape, and always on a rather riduclous
> timeline.
> 
> So how do games, threading, and D all tie into this?
> 
> Ok so I've been following D as a lurker off and on.  From the outside as a
> C++ programmer, D looks great to me.  I literally get more angry working
> with C++ every day.  And its all because doing anything 'cool' in C++,
> particularly templates, requires jumping through hoops.  Jumping through
> hoops is really the reality of having to deal with language deficiencies.
> So looking at D the initial impression is 'sweet' I want to write something
> in that.  Except from my world there are several huge problems:
> 
> Problem A : Garbage Collection is a dealbreaker.  But not because it exists
> or even that is is forced or a default.  We definitely want garbage
> collection.  It is a dealbreaker because of how it behaves.  There are
> several behaviors that make it such a strong negative as to be a
> dealbreaker, primarily the unknown frequency of collections, duration of
> collections, and the fact all our threads get suspended.  The more hardcore
> games run at a required 60 fps (gran turismo, god of war, etc).  This means
> all threads are executing a full cycle in 16.6 ms.  How much time do we want
> the GC to spend?  The answer is 0 ms.  Even spending 1ms for any kind of
> function in any game is pretty damn slow in a game engine.  If it starts
> pushing 5 or 10ms it starts impacting response of input, and noticebly
> hitches the rendering, since this hitch generally isn't every single frame.
> Consistency of the frame rate matters a lot.   In fact consistency matters
> so much that collecting could take 2ms of every 15 and we would be ok with
> it as long at was predictable so we can budget the game around it.  Even if
> it would only really need 10ms every 5 minutes, that is unacceptable,
> because a collector taking 10ms is a dealbreaker.

I think this is one area where D will improve quite a bit over time. 
Personally, the GC I am most interested in is IBM's Metronome (a Java 
GC), and I'm hoping that a similar approach will be possible with D.

> Problem B : Threading support.  The language of the future addresses
> threading head on, understanding that the number of cores on CPU processors
> is going to rapidly be in the tripple digits and beyond.  The chip makers
> have hit a wall, and the gains are going to come predominantly from core
> increases and memory I/O catching back up to the CPUs.  Eventually the line
> between CPU's and GPU's will blur quite a bit.  Which means we need to write
> threadable code safely, efficiently, without jumping through hoops, and not
> even really worrying about it a whole lot.  If our CPU based languages fail
> at this, we are going to be ending up writing game-physics raytracing code
> on the GPU instead via stuff like NVIDIA's GPGPU.  Which is essentially
> going to be stealing GPU performance to make up for the inability to take
> advantage of a massively parallel CPU core architecture.  Languages that are
> created, or are modified to make this leap cleanly will be the dominant
> players of the future.  I believe that if D makes this leap, it will be the
> one of them.  Judging by the progress of c++0x, I believe it has lost the
> agility necessary to make this transition and will be superceded by another
> language at this transition.

D is in a better position than C++ in this respect, and things will only 
get better.  So far, the greatest obstacle has been available time to 
develop such tools.

> My gut feeling says that if the threading issues of are dealt with up front
> it would help a lot with garbage collection, since the requirements of
> moving the data efficiently in a massively threaded environment would drive
> evoloution in the GC system.  Even if the end-result is simply that you can
> construct isolated threads to get private GC heaps, and that data must be
> marshalled to them as if they were in another process space, it would be an
> improvement, because at least then the GC doesnt show down every single
> thread, and thin threads can collect very very fast.

The static data region is still an issue, since it is obviously shared 
between threads.  But it may be that either something could be done with 
multiple specialized allocators, or simply linking against a custom GC 
if you're willing to code to a certain model.  That said, do some 
Googling for Metronome, which I mentioned above.  It's a hard realtime 
GC and would be perfect for games, since they have fairly 
well-established runtime requirements, memory use, etc.


Sean