self vs. global

totebo · December 2016

Can someone (@sinistersoft!) explain why self is consistently slower than global in this code?

Main = Core.class()
 
ITERATIONS = 5000000
TEST_VAR @ 4353
 
global_var = TEST_VAR
 
function Main:init()
 
	self.self_var = TEST_VAR
 
	local t = os.timer()
	for i=1, ITERATIONS do
		global_var = global_var + global_var/global_var
	end
	print( "Global:", os.timer() - t )	
 
	local t = os.timer()
	for i=1, ITERATIONS do
		self.self_var = self.self_var + self.self_var/self.self_var
	end
	print( "Self:", os.timer() - t )
 
	local var_local = TEST_VAR
	local t = os.timer()
	for i=1, ITERATIONS do
		var_local = var_local + var_local/var_local
	end
	print( "Local:", os.timer() - t )
 
end
 
Main.new()

SinisterSoft · December 2016

self variables have to be looked up in a table belonging to whatever self is. Globals are more direct.

n1cke · December 2016

Global: 0.48127102760191
Self: 0.47692719142651
Local: 0.07365396944806
Not on my PC :-)
You compare table access `self.self_var` with global variable `global_var` access time. `self` is just implicit parameter, it's speed is the same as any other local variable/parameter. Lua searches like this:
1) local variable/parameter
2) upvalue
3) global variable
Upvalues and global variables are implicitly stored in tables (`debug` library can access upvalues, `_G` table is for global variables). Therefore global variable access speed for `_G` is similar to usual table access for`self`.

totebo · December 2016

Thanks guys. Yeah, sorry, I meant global vars are consistently slower than self. Thanks for the explanation. I'm going to stick with local vars whenever I can, blimey!

SinisterSoft · December 2016

Hmm - I mean local globals sorry....

Main = Core.class()
 
ITERATIONS = 5000000
TEST_VAR @ 4353
 
local global_var = TEST_VAR

now it should be faster.

totebo · December 2016

Yeah, I'll do that whenever I can. But I can't have the entire game in one scope (can I?!), so in some cases this isn't possible. So I was wondering whether to use self.var or global var, and I think the difference is quite small, but in favour of self.var.

SinisterSoft · December 2016

Use macro constants wherever you can, then the most commonly executed vars that need to be global, use local globals.

totebo · December 2016

Bingo. This is now my mantra.

Howdy, Stranger!

Categories

In this Discussion

Top Posters

self vs. global

Comments

Howdy, Stranger!

Quick Links

Categories

In this Discussion

Top Posters

self vs. global

Comments