Optimize the limits inside the VM

[shargon]

Currently we have a lof of limits in the VM, some of them require in every step recompute the count for ensure that fits the expected values. I think that is too expensive and sometimes could be unfair. For example: One array of 1025 items is not allowed, but two of 1024 yes.

I don't have now the perfect solution but I think that we should improve this.

This method is very expensive, but with our current module is needed:

neo-vm/src/neo-vm/ExecutionEngine.cs

Lines 106 to 121 in 2fd56dd

	private bool CheckStackSize(bool strict, int count = 1)
	{
	is_stackitem_count_strict &= strict;
	stackitem_count += count;
	if (stackitem_count < 0) stackitem_count = int.MaxValue;
	if (stackitem_count <= MaxStackSize) return true;
	if (is_stackitem_count_strict) return false;
	// Deep inspect
	stackitem_count = GetItemCount(InvocationStack.Select(p => p.EvaluationStack).Distinct().Concat(InvocationStack.Select(p => p.AltStack).Distinct()).SelectMany(p => p));
	if (stackitem_count > MaxStackSize) return false;
	is_stackitem_count_strict = true;
	return true;

My proposal is something like this:

class Memory
{
public int Max;
public int Current;
public StackItem CreateInteger(int value)
{
  var ret=new StackItem(value);
  Current+=ret.Size;
  return ret;
}
public void Clean(StackItem i){ Current-=i.Size; }
}
class ApplicationEngine
{
Memory mem;
public ApplicationEngine(Memory mem){ ... }
}

If we centralize the creation of the StackItems in only one point, we will have a control of the current memory without need to recompute in every steps.

Is only an idea, i really know that this great minds @neo-project/ngd-shanghai will have a good ones.

But for me the goal is to have only one limit: 16mb of RAM (for example).

[shargon]

Possible solutions:

• Reference tracing #232
• Optimize memory limits #230

[shargon]

I will close this, and open one only related to the memory logic