Weakref::valid

(PECL weakref >= 0.1.0)

Weakref::valid — Checks whether the object referenced still exists

说明

public Weakref::valid ( void ) : bool

Checks whether the object referenced still exists.

参数

此函数没有参数。

返回值

Returns TRUE if the object still exists and is thus still accessible via Weakref::get(), FALSE otherwise.

参见

  • Weakref::get() - Returns the object pointed to by the weak reference

User Contributed Notes

d dot negrier at nospam dot thecodingmachine dot com 03-May-2018 02:59
Beware that the "valid()" method should not be used to check the availability of an object before calling "get()". Indeed, the garbage collector might be triggered between the call to "valid()" and the call to "get()".

<?php

if ($weakRef->valid()) { // Returns true because the object is not yet garbage collected
    // If you are not lucky, the garbage collector might be triggered here
    $obj = $weakRef->get(); // Returns null
    $obj->doSomeStuff(); // Boom!
}
?>

So instead, you should always call "get()" directly:

<?php
$obj = $weakRef->get();
if ($obj !== null) {
    $obj->doSomeStuff(); // This is 100% accurate
}
?>

Generally speaking, the "valid()" method is tricky because a call to it might return true and the next call might return false (you never know when the garbage collector will be trigerred). However, testing for invalidity works reliably.

<?php
if ($weakRef->valid()) {
    // At this point, you are not sure that the object is still there (garbage collector might have collected it)
}

if (!$weakRef->valid()) {
    // At this point, you are sure the object is gone.
}
?>