php手动释放内存

<?php
$s = str_repeat("1",1024); 
$b = &$s;

$m=memory_get_usage(); //获取当前占用内存
echo $m."
";

//unset($s);
//$s = null;

$mm = memory_get_usage(); //unset()后再查看当前占用内存
echo $mm . "
";


echo $m -$mm ;
echo "
";
?>

结论：

1, unset只是变量计数器减1，,当计数器为0的时候会触发回收

2, $s=null 会直接触发回收