(PECL weakref >= 0.1.0)
Weakref::acquire — Acquires a strong reference on that object
Acquires a strong reference on that object, virtually turning the weak reference into a strong one.
The Weakref instance maintains an internal acquired counter to track outstanding strong references. If the call to Weakref::acquire() is successful, this counter will be incremented by one.
This function has no parameters.
   Returns TRUE if the reference was valid and could be turned into a strong
   reference, FALSE otherwise.
  
Example #1 Weakref::acquire() example
<?php
class MyClass {
    public function __destruct() {
        echo "Destroying object!\n";
    }
}
$o1 = new MyClass;
$r1 = new Weakref($o1);
$r1->acquire();
echo "Unsetting o1...\n";
unset($o1);
$o2 = $r1->get();
$r1->release();
echo "Unsetting o2...\n";
unset($o2);
?>
The above example will output:
Unsetting o1... Unsetting o2... Destroying object!
Example #2 Nested acquire/release example
<?php
class MyClass {
    public function __destruct() {
        echo "Destroying object!\n";
    }
}
$o1 = new MyClass;
$r1 = new Weakref($o1);
echo "Acquiring...\n";
$r1->acquire();
echo "  Unsetting...\n";
unset($o1);
echo "  Acquiring...\n";
$r1->acquire();
echo "    Acquiring...\n";
$r1->acquire();
echo "    Releasing...\n";
$r1->release();
echo "  Releasing...\n";
$r1->release();
echo "Releasing...\n";
$r1->release();
?>
The above example will output:
Acquiring...
  Unsetting...
  Acquiring...
    Acquiring...
    Releasing...
  Releasing...
Releasing...
Destroying object!