How fast is this?

Performance Tuning
#1

Hi all,
I have a forloop which loops through an ArrayList full of Entities.

What the for loop does is that it loops through the arraylist, obtains the Entity from the arraylist, then does a Entity.Hashmap.get(arg_name); if its true, then break.

So here it is in code:


public void getEntity(Spatial s) {
  String name = s.getName();
  for (int i = 0; i < entityArrayList.size(); i++) {
    Entity t = (Entity) entityArrayList.get(i);
    boolean hasName = t.containsSpatialName(name);
    if (hasName == true) break;
  }
}

Thats all it does. The only problem is that its in the same thread as the renderer (and I dont whish to change that). The ArrayList will by large have around at max 5000 Entities and I was wondering how fast this is and how large of an FPS hit would I have to bear.

Thx, DP

#2

Is it just me, or does that loop not do anything? ;D

Anyway, to answer your question: blindingly fast. Each operation will execute so fast you could blink and not see it happen :P.

Think about it: you’re asking us to tell you how fast a particular loop runs on any unknown PC. Perhaps you could instead ask something quantified and important like “realistically, can I call hashCode() more than 1 million times every 1 ms on a modern PC?”. Or something like “are there any performance problems with Arraylists with 5000 elements?” (to which the answer is YES!: be a little careful about add’s, and especially careful about indexOf’s and remove’s, which can be slow on mor than a few thousand elements)

OTOH, how many times do people have to say “optimize last” and “profile before optimizing”?

The question “this code is responsible for 65% of my runtime, which I can’t explain at all” then that would be a very good question for people to help with. As it stands, it’s a little hard to see how it could even show up at all in your profiler…

#3

the above code was an extract, and is not intended to be full code. Here is the full code:


public Entity getEntity(Spatial s) { 
  String name = s.getName(); 
  for (int i = 0; i < entityArrayList.size(); i++) { 
    Entity t = (Entity) entityArrayList.get(i); 
    boolean hasName = t.containsSpatialName(name); 
    if (hasName == true) return t; 
  }
}

The reason I ask is because I cannot create a test case where that is the case, this is pure speculation and the possibility of it happening is there. If this will be the downfall of the FPS, then perhaps I should design in a different matter.

As for the arraylist comment, there will be no IndexOf calls, perhaps some remove (but that is rare).

I dont have a profiler because I dont have the money to buy either OptimiseIT or JProbe.

I should have said, “Is this design with speed on mind sound?” rather than “is this fast”

DP

#4

Then I think the most important answer for you is “I don’t see anything stupid in there” (of course, I might have missed something ;)) - i.e. the actual code is not so spectacularly bad that it will fundamentally blow up (e.g. it’s not iterating over the values of a hashtable, which is definitely a bad thing to do).

As to profiling, java comes with a free profiler. As Cas has explained lots of times in the past (which is why I dislike forums for programming - his comments are now buried somewhere in the distant past of his 3000 posts!), that free profiler is more than sufficient to do 90% of your profiling work. It doesn’t draw fancy graphs, it doesn’t produce colourful output, and it doesn’t have a GUI. But…it does give you a very simple statement “these are the slowest parts of your program, this is how slow they are, and here are the line numbers” - which is all you need, really, unless you’re doing exceptional stuff.