Hello,

you are right that there is some race-condition to valid() followed by get() that makes it somewhat dangerous to trust as is.

Have you tried to acquire() the weak ref instead of checking valid()? If acquire is successful you should be safe to get() it until you release().

Best
 Instead of deprecating valid() or disabling the GC in the middle of the critical section, how about you simply acquire() the weakref? If this returns true, you know that it is safe to get, which you can then release() later.

Hey Etienne,

Thanks a lot for the quick reply.

You are perfectly right that using "acquire" makes a lot of sense and solves the race condition:

```
if ($weakref->acquire()) {
    $myobj = $weakref->get();
    $myobj->doSomeStuff();
    $weakref->release();
}
```

This is great.

But you are kind of proving my point: the "valid" method is useless in this case since it is indeed replaced by acquire.
There are very few cases where "valid()" is useful and it is too tempting to use it. A proper warning in the doc might save some people.

It occurs to me that any action on an object returned by ::get()
without an explicit ::acquire() is potentially prone to memory
management issues.

Hello,

I'm not sure what you mean?

If at the time of the get() call the weakref is still valid, it will increase its refcount as it returns an actual zval of it. From that point on and until it is destroyed, the weakref reference will not be collectible as it has a >=1 refcount.

Ah, thanks!  So ::acquire()/::release() is not strictly
necessary, so that the example above could also be written as:

  if (($myobj = $weakref->get())) {
      $myobj->doSomeStuff();
  }

@cmb: absolutely.

Actually, if you want to fetch an object from a WeakRef, the correct way to go is:

<?php
if ($myobj = $weakref->get()) {
    $myobj->doSomeStuff();
}
?>

My whole point is that it is too easy for a beginner using this function to write:

<?php
if ($weakref->valid()) { // returns true
    // If you are unlucky, the garbage collector might be triggered here
    $myobj = $weakref->get(); // will return null
    $myobj->doSomeStuff(); // boom
}
?>

This is wrong because the garbage collector may be triggered between first and second line.

I added a user contributed note on the "WeakRef::valid()" method page. It should be published soon. http://php.net/manual/en/weakref.valid.php

Since PECL/Weakref is no longer maintained (it is inherently
incompatible with PHP 7.3+), I'm closing this.