3 ms·

can you even do that? In Java you can't allocate any List like data strucutre (LinkedList, ArrayList, arrays (Maps of course)) on the heap. Escape analysis migh

• DougBTX 9y ago
  A key idea is reducing churn, not simply avoiding allocation at all. For example, if the code which renders a frame always needs a four byte array each time it runs, it could reuse the same array each time, rather than allocating then garbage collecting each time.
• Kapura 9y ago
  So, I'm not sure what the situation is with Java, but I suspect there might be some confusion in what you're reading. In C#, anything instantiated as part of a class goes onto the heap. Value types that are declared and used only within the function are allocated onto the stack. For example: public class Example { public int a; // Allocated onto the heap when Example is instanced public int b; // Allocated onto the heap when Example is instanced public int c; // Allocated onto the heap when Example is instanced public void CycleValues() { int temp = a; // Allocated onto the stack when function is called a = b; // a, b, and c are already allocated b = c; c = temp; // temp goes away when the function finishes executing } public int SumPositiveValues() { List<int> positiveList = new List(); // Not a value type: allocates onto the heap if (a > 0) valueList.Add(a); if (b > 0) valueList.Add(b); if (c > 0) valueList.Add(c); int sum = 0; // Allocated onto the stack foreach (int i in valueList) { sum += i; } return sum; // sum goes away when the function finishes executing // positiveList was allocated onto the heap, so it persists (although inaccessible) until garbage collection } } In the example above, space on the heap is allocated when you create a new Example(). Calling CycleValues() doesn't allocate anything new onto the heap, so it isn't creating any garbage. Calling SumPositiveValues() creates a new List(), which, not being a value type, is allocated onto the heap. When the function finishes, that memory isn't automatically freed; it creates garbage. Optimising for heap performance relies a lot on removing New calls to classes when it is possible and makes sense to do so.
  • merb 9y ago
    well thats what I meant. Basically I'm not a game dev, but keeping simple values on the stack is most often not a problem. However it's insane how many Lists, Arrays I need and I'm a web developer. So I guess a Game Dev even needs more of these (Inventory, Stats, Chat, whatever)
    • Kapura 9y ago
      Yeah, but the big key is to keep things instantiated only once (where reasonable). So, if I'm making an RTS, I keep only one list of selected units, and it persists even if I have no units selected. No reallocation or losing the reference means nothing is getting garbage collected. There are bigger convos to be had about data architecture here, but now's neither time nor place for it.
• zaptheimpaler 9y ago
  You could always use byte array or ByteBuffer and reinvent the data structures with raw bytes right ? I imagine thats what you would have to do... sounds exciting.