How to free memory in PHP?

Question

public function foo($file1, $file2){
  $obj = new Obj();

  $data = array();
  $data[] = $obj->importAFile($file1);
  $data[] = $obj->importAFile($file2);

  return $data;
}

Does the memory allocated for $obj get freed after the return?

If not how can I free it?

Answer 1

By using unset() on a variable, you've marked it for 'garbage collection' literally, as PHP doesn't really have one, so the memory isn't immediately available. The variable no longer houses the data, but the stack remains at the current size even after calling unset(). Setting the variable to NULL drops the data and shrinks the stack memory almost immediately.

This has worked for me on several occasions where memory exhausted warnings were thrown before the tuning, then calling unset() after nullifying the variable. Calling unset after nullifying mightn't be necessary but I used it nonetheless after the nullification.

Answer 2

PHP uses garbace collector. It frees all variables to which there are no references left. Assuming that $obj->importAFile() does not return reference to $obj, the memory will be freed. However, there is no guarantee when the memory will be freed. If $obj contains reference to itself, in older versions of PHP the memory won't be freed as well. You can read more in PHP documentation