5 ms·

GC is the killer of hard real time constraints

BoorishBears 9y ago
GC doesn't kill constraints for games. Unity3D games have been dealing with the GC for ages now, it's not that bad. Cautious use of memory allocations and calling the GC at convenient times go a long way. But on the other hand Java doesn't have value types, which is pretty terrible.
- Thaxll 9y ago
  Yes it kills it, there is no big AAA game running on Unity, try to do a Battlefield like game with a GC language where every ms count.
  - BoorishBears 9y ago
    That's actually exactly my point, "kills real time constraints" is very strong language, you end up having to look at AAA games the size of Battlefield to see where it falls short. Minecraft-like games with similar voxel rendering can, and have been, done in Unity. In fact on the internal Nintendo Wii U dev forums I recall a Minecraft-clone was deep in development in Unity, but I think a lack of demand on the platform killed it
    - ferongr 9y ago
      A "demo" (with all the limitations and corner-cutting that demos usually employ) is one thing, a complete product is a different beast.
- vvanders 9y ago
  > Cautious use of memory allocations... I believe you're arguing against a GC there.
- glenneroo 9y ago
  I can only speak for Kerbal Space Program, but Unity 5's GC causes stutters on many people's systems, regardless how much RAM is available. There is a wonderful plugin called MemGraph[0] which lets you view GC events and more importantly, to change the time and frequency of GC activation, which has almost completely alleviated stuttering on many systems (my own included). [0]http://forum.kerbalspaceprogram.com/index.php?/topic/139128-12x-memgraph-1103-with-stutter-reduction/ http://forum.kerbalspaceprogram.com/index.php?/topic/139128-...
  - BoorishBears 9y ago
    Working with the GC is definitely tricky, but I think it's a feature that works well for the majority of the games made with Unity and really only rears it's head in specific types of games of a specific size. Saying it kills realtime constraints for gaming is definitely a stretch. Open world games with no transitions for example, leave little room for natural GC calls, where as level based games can do things like call the GC at the start of each level and carefully budget allocations through out the level.
    - ferongr 9y ago
      The "majority" of games made in Unity are very constrained mechanically and developers have control over the complete experience.
  - deleted 9y ago
    [deleted]
- webkike 9y ago
  "not that bad" is still something that "I don't want to deal with" when I'm making a game. Get rid of GC pauses and let me allocate memory.
  - BoorishBears 9y ago
    It's great that works for you, and there's plenty of ways to take that approach outside of Unity. Like anything technology there are trade offs, having a GC while minimizing allocations can save a lot of time and effort upfront. I see it as Python vs Java, or NoSQL vs SQL, or a host of other similar comparisons that rage on in programming.
ungzd 9y ago
Why then Minecraft works perfectly on PC (even worked perfectly in 2009)?
- webkike 9y ago
  I personally never checked the fps when playing Minecraft but Minecraft was not extremely computationally intensive. Despite that they still needed to port it to a non GC language to get it running on phones
  - favorited 9y ago
    Beyond just getting it running on phones, C++ is the industry standard for cross-platform games.
- skybrian 9y ago
  On my Mac back when I used to play a couple years ago, I saw random slowdowns. I tried various voodoo Java VM parameter tweaking and it didn't entirely fix it. Based on my searches I'm not alone. Maybe it worked perfectly on your boxes, but there's something rather fragile and machine-dependent about Minecraft performance.
- PhasmaFelis 9y ago
  It certainly didn't work perfectly in 2009. I had to turn off transparent blocks and greatly reduce the draw distance to get decent framerates on my laptop at the time. Maybe you had a better PC then I did. Java Minecraft still requires at least 10x more processing power than it would in a more suitable language.
- jamesgeck0 9y ago
  Java Minecraft definitely used to have lots of issues with large worlds on my 2009 laptop. Low framerates with freezes every time a new region was loaded, even with draw distance on the lowest setting.
- khedoros1 9y ago
  Did you ever look at the framerate graph and see the stutter caused by GC? Every time the "allocated memory" counter jumps down, you've got a few frames worth of pause in the graphics, and a big red latency line in the graph.
pkulak 9y ago
That's true, but no game is hard real time.
devrandomguy 9y ago
What memory management paradigm would you recommend, for an application like this? Let's say, a 1 hour game session generates ~100 GB of transient data, but only 100 MB is needed for what is currently within the camera's view at any one time. How do you keep track of which data is still important, and when do you release memory?
- webkike 9y ago
  Probably spatial partitioning, although who knows. These things are suitable for theoretics. One must find the best solution.

GC doesn't kill constraints for games. Unity3D games have been dealing with the GC for ages now, it's not that bad. Cautious use of memory allocations and calling the GC at convenient times go a long way. But on the other hand Java doesn't have value types, which is pretty terrible.

Thaxll 9y ago
Yes it kills it, there is no big AAA game running on Unity, try to do a Battlefield like game with a GC language where every ms count.
- BoorishBears 9y ago
  That's actually exactly my point, "kills real time constraints" is very strong language, you end up having to look at AAA games the size of Battlefield to see where it falls short. Minecraft-like games with similar voxel rendering can, and have been, done in Unity. In fact on the internal Nintendo Wii U dev forums I recall a Minecraft-clone was deep in development in Unity, but I think a lack of demand on the platform killed it
  - ferongr 9y ago
    A "demo" (with all the limitations and corner-cutting that demos usually employ) is one thing, a complete product is a different beast.
vvanders 9y ago
> Cautious use of memory allocations... I believe you're arguing against a GC there.
glenneroo 9y ago
I can only speak for Kerbal Space Program, but Unity 5's GC causes stutters on many people's systems, regardless how much RAM is available. There is a wonderful plugin called MemGraph[0] which lets you view GC events and more importantly, to change the time and frequency of GC activation, which has almost completely alleviated stuttering on many systems (my own included). [0]http://forum.kerbalspaceprogram.com/index.php?/topic/139128-12x-memgraph-1103-with-stutter-reduction/ http://forum.kerbalspaceprogram.com/index.php?/topic/139128-...
- BoorishBears 9y ago
  Working with the GC is definitely tricky, but I think it's a feature that works well for the majority of the games made with Unity and really only rears it's head in specific types of games of a specific size. Saying it kills realtime constraints for gaming is definitely a stretch. Open world games with no transitions for example, leave little room for natural GC calls, where as level based games can do things like call the GC at the start of each level and carefully budget allocations through out the level.
  - ferongr 9y ago
    The "majority" of games made in Unity are very constrained mechanically and developers have control over the complete experience.
- deleted 9y ago
  [deleted]
webkike 9y ago
"not that bad" is still something that "I don't want to deal with" when I'm making a game. Get rid of GC pauses and let me allocate memory.
- BoorishBears 9y ago
  It's great that works for you, and there's plenty of ways to take that approach outside of Unity. Like anything technology there are trade offs, having a GC while minimizing allocations can save a lot of time and effort upfront. I see it as Python vs Java, or NoSQL vs SQL, or a host of other similar comparisons that rage on in programming.

ungzd 9y ago

Why then Minecraft works perfectly on PC (even worked perfectly in 2009)?

webkike 9y ago
I personally never checked the fps when playing Minecraft but Minecraft was not extremely computationally intensive. Despite that they still needed to port it to a non GC language to get it running on phones
- favorited 9y ago
  Beyond just getting it running on phones, C++ is the industry standard for cross-platform games.
skybrian 9y ago
On my Mac back when I used to play a couple years ago, I saw random slowdowns. I tried various voodoo Java VM parameter tweaking and it didn't entirely fix it. Based on my searches I'm not alone. Maybe it worked perfectly on your boxes, but there's something rather fragile and machine-dependent about Minecraft performance.
PhasmaFelis 9y ago
It certainly didn't work perfectly in 2009. I had to turn off transparent blocks and greatly reduce the draw distance to get decent framerates on my laptop at the time. Maybe you had a better PC then I did. Java Minecraft still requires at least 10x more processing power than it would in a more suitable language.
jamesgeck0 9y ago
Java Minecraft definitely used to have lots of issues with large worlds on my 2009 laptop. Low framerates with freezes every time a new region was loaded, even with draw distance on the lowest setting.
khedoros1 9y ago
Did you ever look at the framerate graph and see the stutter caused by GC? Every time the "allocated memory" counter jumps down, you've got a few frames worth of pause in the graphics, and a big red latency line in the graph.

pkulak 9y ago

That's true, but no game is hard real time.

devrandomguy 9y ago

What memory management paradigm would you recommend, for an application like this? Let's say, a 1 hour game session generates ~100 GB of transient data, but only 100 MB is needed for what is currently within the camera's view at any one time. How do you keep track of which data is still important, and when do you release memory?

webkike 9y ago
Probably spatial partitioning, although who knows. These things are suitable for theoretics. One must find the best solution.