note 54823 deleted from language.variables.scope by danbrown

Note Submitter: www dot php dot net dot 2nd at mailfilter dot com dot ar ---- I've been doing some performance tests. I thought I could squeeze some extra cyles using references, but I discovered they are more mysterious than I imagined (5.0.3). Consider this: $a = str_repeat('hola',10000000); for($n = 0 ; $n < 1000000 ; $n++ ) { $b = $a; unset($b); } real 0m1.514s user 0m1.433s sys 0m0.071s The above times (as others in this note) are the best out of three attempts in an idle Linux box. I expected the above to be a bit slow, since constructing $b might imply copying the 40MB string each time. It was very fast, though. Let's try with references: $a = str_repeat('hola',10000000); for($n = 0 ; $n < 1000000 ; $n++ ) { $b =& $a; unset($b); } real 0m1.488s user 0m1.380s sys 0m0.071s Not much of a gain, but it did took less time to complete. Will this work with functions? Let's see: $a = str_repeat('hola',10000000); for($n = 0 ; $n < 1000000 ; $n++ ) dosome($a); function dosome($arg){ $t = strlen($arg); } real 0m3.518s user 0m3.276s sys 0m0.088s Mmm... much slower, but still pretty nice. I didn't use references yet, so let's try them out: $a = str_repeat('hola',10000000); for($n = 0 ; $n < 100 ; $n++ ) dosome($a); function dosome(&$arg){ $t = strlen($arg); } real 0m12.071s user 0m6.190s sys 0m5.821s You think it is 3.5 times slower? Think again. It is 350,000 times slower. I had to limit the $n loop to 100 iterations in order to get those figures! I wonder what happens if I try to access the variable globally: $a = str_repeat('hola',10000000); for($n = 0 ; $n < 1000000 ; $n++ ) dosome(); function dosome(){ $t = strlen($GLOBALS['a']); } real 0m3.007s user 0m2.918s sys 0m0.074s Notice that using $GLOBALS we're back in bussiness. So using the global keyword should be exactly the same, isn't it? Wrong again: $a = str_repeat('hola',10000000); for($n = 0 ; $n < 100 ; $n++ ) dosome(); function dosome(){ global $a; $t = strlen($a); } real 0m12.423s user 0m6.112s sys 0m5.917s We're in the '350,000 times slower' domain again. I wonder why the script is spending so much time in sys. A couple of additional tests to complete the puzzle: $a = str_repeat('hola',10000000); $b = Array(&$a); for($n = 0 ; $n < 100 ; $n++ ) dosome(); function dosome(){ $t = strlen($GLOBALS['b'][0]); } real 0m12.087s user 0m6.068s sys 0m5.955s $a = str_repeat('hola',10000000); $b = Array(&$a); for($n = 0 ; $n < 100 ; $n++ ) dosome(); function dosome(){ global $b; $t = strlen($b[0]); } real 0m12.158s user 0m6.023s sys 0m5.971s I guess the $GLOBALS trick doesn't help when we access a reference stored in the global variable. I'm completely confused, now. At this light, I will review my usage of the global keyword as well as for the references. I hope someone can benefit from this study too.