Using Closures as callbacks within loops
In jQuery (and other Javascript frameworks) it is quite common to use closures (I refer to them as callback functions) to loop over arrays or objects. Even though it's a slow process and is much more efficient to use the built-in for loop, it got me thinking. Why not try and use the new Closure class in PHP 5.3 and see how well it performs within a loop? Suffice to say, I got some really really interesting results. Before I get into the details, here is the test script I wrote (the Benchmark class is merely a class I have written in the past).
<?php $data = range(0, 1000);
$clean = array();
public function loop($array, Closure $closure) {
if (!empty($array)) {
foreach ($array as $key => $value) {
$closure($key, $value);
}
}
}
Benchmark::start('loop');
foreach ($data as $key => $value) {
$clean[$key] = $value;
}
loop($data, function($key, $value) {
$clean[$key] = $value;
});
Benchmark::stop('loop');
echo Benchmark::display('loop'); ?>I didn't get too in depth with my test cases and simply used Firefox and page refresh to get my results. I am running PHP 5.3.1 on a Windows 7 XAMPP installation with Apache and no caching. For benchmarking I was using microtime(true) and memory_get_usage().
I began testing with 4 different cases, each of which that changed the size of the $data array. I started with 1000 iterations, then 5000, then 10000 and lastly 100000. I would comment out the foreach/loop sections and run them one at a time (of course), and ran each test about 5 times to gather an average. Here are the results.
foreach:
1000 Time: 0.0010 / Memory: 137128 (Max: 689160)
5000 Time: 0.0052 / Memory: 706488 (Max: 1258528)
10000 Time: 0.0097 / Memory: 1412048 (Max: 1964120)
100000 Time: 0.0545 / Memory: 13849568 (Max: 14401656)
closure:
1000 Time: 0.0027 / Memory: 84984 (Max: 688832)
5000 Time: 0.0144 / Memory: 433672 (Max: 1258192)
10000 Time: 0.0267 / Memory: 866448 (Max: 1963744)
100000 Time: 0.1223 / Memory: 8525216 (Max: 14401256)The first thing you will notice is the time it took to interpret the page. On average using a closure as a callback within a loop will take 2-3x longer to process. However, the interesting thing is that the memory usage is around 40% smaller (using more allocated memory) while using a closure than doing a foreach, yet the max allocated is nearly identical. I knew what the outcome would be before I even started it -- Javascript closures are the same way. Regardless it was a fun experiment and if anyone knows more about this, please shed some light on this topic for the rest of us!
But in closing I can sadly say, that no, you should not be using a closure for looping, just stick to the old fashion tried and true foreach or for loop.