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Date: Sat, 22 Jan 2022 19:01:42 +0000
Message-ID: <CAFKaYMo7tLLi-A1er=w-SA181kDDEZNhCE7yRE+QfCUS1ZtODA@mail.gmail.com>
To: "Christoph M. Becker" <cmbecker69@gmx.de>
Cc: PHP internals <internals@lists.php.net>
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Subject: Re: Weak Closures
From: codekestrel@googlemail.com (Dominic Grostate)

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That's very strange, I had thought it might be a bug. For simple use cases
where an object references it's own closure it might be a memory leak, but
for complex event loops it potentially allows unnecessary code to run
indefinitely.

I'm afraid I don't know any more than that. Thanks for the tip though.

On Sat, 22 Jan 2022, 15:30 Christoph M. Becker, <cmbecker69@gmx.de> wrote:

> On 21.01.2022 at 11:31, Dominic Grostate wrote:
>
> > I'd like to express my interest in a possible feature concerning weak
> > references. Currently closures created within a class appear to
> > contain a reference to the object that created it. This is of course
> > necessary in order for the closure to retain the necessary scope.
> > However I would like to suggest we have the option for closure to
> > weakly reference this object so that when the object is garbage
> > collected, the closure too may be rendered null or invalid
> > (inspectable).
> >
> > Consider the following example:
> > https://gist.github.com/orolyn/7651e4127759aad1736547490baa1394
> >
> > The idea here is that without unset($sample) the loop would run
> > forever, because there is a reference to the callback from the object,
> > and in turn there is a reference to the object from the main stack.
> > With the unset($sample), the idea is that before the callback is even
> > called, the reference to the object is destroyed thusly so is the
> > reference to callback, and since the callback is only referenced now
> > in a WeakMap, the callback will finally be gone.
> >
> > In reality it appears there is a circular reference between the object
> > and the callback. I don't know if this is a bug or not, because from
> > what I can find PHP was fixed a long time ago to resolve circular
> > references.
> >
> > However if this is intentional, I would like the option to make the
> > closure weak for example:
> >
> > $c = WeakClosure::fromCallable(function () {});
> > $c = Closure::fromCallable(function () {}, true);
> >
> > Please let me know your thoughts, because maybe there is a way of
> > achieving this with PHP as is.
>
> If you trigger the garbage collector manually (i.e. call
> gc_collect_cycles() after unset($callback)), the loop terminates right
> away.  I'm not sure why it doesn't without manually triggering the GC.
>
> Christoph
>

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