PHP - 有一种安全的方法来执行深度递归吗？

Question

Im talking about performing a deep recursion for around 5+ mins, something that you may have a crawler perform. in order to extract url links and and sub-url links of pages

it seems that deep recursion in PHP does not seem realistic

e.g.

getInfo("www.example.com");

function getInfo($link){
   $content = file_get_content($link)

   if($con = $content->find('.subCategories',0)){
      echo "go deeper<br>";
      getInfo($con->find('a',0)->href);
   }

   else{
      echo "reached deepest<br>";
   }
}

Answer 1

Doing something like this with recursion is actually a bad idea in any language. You cannot know how deep that crawler will go so it might lead to a Stack Overflow. And if not it still wastes a bunch of memory for the huge stack since PHP has no tail-calls (not keeping any stack information unless necessary).

Push the found URLs into a "to crawl" queue which is checked iteratively:

$queue = array('www.example.com');
$done = array();
while($queue) {
    $link = array_shift($queue);
    $done[] = $link;
    $content = file_get_contents($link);
    if($con = $content->find('.subCategories', 0)) {
        $sublink = $con->find('a', 0)->href;
        if(!in_array($sublink, $done) && !in_array($sublink, $queue)) {
            $queue[] = $sublink;
        }
    }
}