Description:
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Because closures inside classes implicitly have a reference to $this, if a closure is used as a class property, this automatically creates a cyclic reference.

Having read the page on GC here: http://php.net/manual/en/features.gc.collecting-cycles.php I can understand the problem, but the issue this causes is a memory leak any time a closure is used as a class property (Or in an array/data structure in a class property)

Consider the following code:

<?php
class X {
	private $largeStr;
	private $closure;

	public function foo() {
		$this->largestr = str_repeat('ABC', 10000000);

		$this->closure = function() {};
	}
}




echo (memory_get_usage()/1024/1024) . 'mb<br >';

for ($i = 0; $i < 1000; $i++) {
	$x = new X;
	$x->foo();
	unset($x);
	echo (memory_get_peak_usage()/1024/1024) . 'mb<br >';
}

?>

Which outputs:

0.21446228027344mb
28.827682495117mb
57.438827514648mb
86.050003051758mb
114.66118621826mb

Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 30000001 bytes)


I have explicitly called unset() which I would hope would free the memory used by the class, clearly it doesn't. Similarly, adding 


	public function __destruct() {
		unset($this->closure);
	}

to the class does not help.



I'm not sure there is an obvious fix for this but gc_collect_cycles() in the loop does solve it, I have to wonder why unset() doesn't just trigger gc_collect_cycles(). Presumably it can do it in a smarter way as well because it doesn't have to look through every defined variable.