Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:126667
Precedence: bulk
MIME-Version: 1.0
References: <CAMW7n8AJckEDzhGv9BdjNhq8zAdCqb4HsVr56vGi+izw50X6Dg@mail.gmail.com>
 <9964db8c-0ffe-43d5-8246-47fc76b07180@app.fastmail.com> <CAMW7n8CM7oBfXCDsKtV4hTFs40UmLCU3183WjYE2exLNqKDWLQ@mail.gmail.com>
 <78a03dd0-fd4a-4f4a-ad8a-37e5704f06fc@app.fastmail.com> <CAMW7n8C-Z18MKhyDX2+ofg70cRbwWOk=YWDAZpKtfLZsFVVRng@mail.gmail.com>
 <bb7a9f8f-0422-45e5-b4fc-f5757add92b4@app.fastmail.com> <CAMW7n8BnzL7d0bd_Y_jGOmyWegKQpm-FzrVFRCcDe=bNFZpi+A@mail.gmail.com>
 <08c8ad0b-e8f4-46e3-99f0-b80748d40b89@app.fastmail.com> <07973EAE-2D83-47A8-8FA0-84286C77C02B@rwec.co.uk>
 <48d66433-3ae9-4895-8361-7c81a0a3670d@app.fastmail.com> <be7cb263-93a1-4bd8-9416-ae4d3e0bafe6@rwec.co.uk>
 <dbce8889-016a-4c59-864c-d8fdec895adc@app.fastmail.com> <CAM0Ccxh=bydoDEHBAV+Gb1_86HJjwhW06kzEsdRiMh93k1F7oA@mail.gmail.com>
 <8599eb8b-d4a3-4cb8-899a-25b134e0d64d@gmail.com> <D73BCCC4-3547-45B4-84AD-A5FD6569D43C@rwec.co.uk>
 <74c4c726-63aa-44e0-84c9-840e13a65a4f@gmail.com> <9b7ab30f-5ed6-400d-b941-1291e9185286@app.fastmail.com>
 <9a2e81e8-3534-455b-879a-5a45c85b3ba7@gmail.com> <CAMW7n8BRwZH64mULctRS4CxOL9TCo5GHvz-ORWHMZr926ZujYw@mail.gmail.com>
 <CAAwdEzALuRtkWyw1JgRVVmU9ew8uTiY6DSruR2CKiqNQ03QzOw@mail.gmail.com>
In-Reply-To: <CAAwdEzALuRtkWyw1JgRVVmU9ew8uTiY6DSruR2CKiqNQ03QzOw@mail.gmail.com>
Date: Sun, 9 Mar 2025 10:05:06 +0200
Message-ID: <CAMW7n8A17ER8vUkNNrEsbkyGm2xY-ZAxkR1_ofWcHmgFbNrzqg@mail.gmail.com>
Subject: Re: [PHP-DEV] PHP True Async RFC
To: =?UTF-8?Q?Alexandru_P=C4=83tr=C4=83nescu?= <drealecs@gmail.com>
Cc: Daniil Gentili <daniil.gentili@gmail.com>, PHP internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary="000000000000eba588062fe450cd"
From: edmond.ht@gmail.com (Edmond Dantes)

--000000000000eba588062fe450cd
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

Good day, Alex.

>
>  Can you please share a bit more details on how the Scheduler is
implemented, to make sure that I understand why this contradiction exists?
Also with some examples, if possible.
>

```php
$fiber1 =3D new Fiber(function () {
    echo "Fiber 1 starts\n";

    $fiber2 =3D new Fiber(function () use (&$fiber1) {
        echo "Fiber 2 starts\n";

        Fiber::suspend(); // Suspend the inner fiber
        echo "Fiber 2 resumes\n";

    });

});
```

Yes, of course, let's try to look at this in more detail.
Here is the classic code demonstrating how Fiber works. Fiber1 creates
Fiber2. When Fiber2 yields control, execution returns to Fiber1.

Now, let's try to do the same thing with Fiber3. Inside Fiber2, we create
Fiber3. Everything will work perfectly=E2=80=94Fiber3 will return control t=
o Fiber2,
and Fiber2 will return it to Fiber1=E2=80=94this forms a hierarchy.

Now, imagine that we want to turn Fiber1 into a *Scheduler* while following
these rules.
To achieve this, we need to ensure that all Fiber instances are created
from the *Scheduler*, so that control can always be properly returned.

```php

class Scheduler {
    private array $queue =3D [];

    public function add(callable $task) {
        $fiber =3D new Fiber($task);
        $this->queue[] =3D $fiber;
    }

    public function run() {
        while (!empty($this->queue)) {
            $fiber =3D array_shift($this->queue);

            if ($fiber->isSuspended()) {
                $fiber->resume($this);
            }
        }
    }

    public function yield() {
        $fiber =3D Fiber::getCurrent();
        if ($fiber) {
            $this->queue[] =3D $fiber;
            Fiber::suspend();
        }
    }
}

$scheduler =3D new Scheduler();

$scheduler->add(function (Scheduler $scheduler) {
    echo "Task 1 - Step 1\n";
    $scheduler->yield();
    echo "Task 1 - Step 2\n";
});

$scheduler->add(function (Scheduler $scheduler) {
    echo "Task 2 - Step 1\n";
    $scheduler->yield();
    echo "Task 2 - Step 2\n";
});

$scheduler->run();

```

So, to successfully switch between Fibers:

   1. A Fiber must return control to the *Scheduler*.
   2. The *Scheduler* selects the next Fiber from the queue and switches to
   it.
   3. That Fiber then returns control back to the *Scheduler* again.

This algorithm has one drawback: *it requires two context switches instead
of one*. We could switch *FiberX* to *FiberY* directly.

Breaking the contract not only disrupts the code in this RFC but also
affects Revolt's functionality. However, in the case of Revolt, you can
say: *"If you use this library, follow the library's contracts and do not
use Fiber directly."*

But PHP is not just a library, it's a language that must remain consistent
and cohesive.

>
>  Reading the RFC initially, I though that the Scheduler is using fibers
for everything that runs.
>

Exactly.

>
>  You mean that when one of the fibers started by the Scheduler is
starting other fibers they would usually await for them to finish, and that
is a blocking operating that blocks also the Scheduler?
>

When a *Fiber* from the *Scheduler* decides to create another *Fiber* and
then tries to call blocking functions inside it, control can no longer
return to the *Scheduler* from those functions.

Of course, it would be possible to track the state and disable the
concurrency mode flag when the user manually creates a *Fiber*. But=E2=80=
=A6 this
wouldn't lead to anything good. Not only would it complicate the code, but
it would also result in a mess with different behavior inside and outside
of *Fiber*.

This is even worse than calling *startScheduler*.

The hierarchical switching rule is a *design flaw* that happened
because a *low-level
component* was introduced into the language as part of the implementation
of a *higher-level component*. However, the high-level component is in
*User-land*, while the low-level component is in *PHP core*.

It's the same as implementing $this in OOP but requiring it to be
explicitly passed in every method. This would lead to inconsistent behavior=
.

So, this situation needs to be resolved one way or another.

--

Ed

--000000000000eba588062fe450cd
Content-Type: text/html; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

<div dir=3D"ltr">Good day, Alex.<div><br></div><div>&gt;<br>&gt;=C2=A0

Can you please share a bit more details on how the Scheduler is implemented=
, to make sure that I understand why this contradiction exists? Also with s=
ome examples, if possible.<br>&gt;<br><br>```php</div><div>$fiber1 =3D new =
Fiber(function () {<br>=C2=A0 =C2=A0 echo &quot;Fiber 1 starts\n&quot;;<br>=
<br>=C2=A0 =C2=A0 $fiber2 =3D new Fiber(function () use (&amp;$fiber1) {<br=
>=C2=A0 =C2=A0 =C2=A0 =C2=A0 echo &quot;Fiber 2 starts\n&quot;;<br><br>=C2=
=A0 =C2=A0 =C2=A0 =C2=A0 Fiber::suspend(); // Suspend the inner fiber<br>=
=C2=A0 =C2=A0 =C2=A0 =C2=A0 echo &quot;Fiber 2 resumes\n&quot;;<br><br>=C2=
=A0 =C2=A0 });<br><br>});<br>```</div><div><br></div><div><p>Yes, of course=
, let&#39;s try to look at this in more detail.<br>
Here is the classic code demonstrating how <code>Fiber</code> works. <code>=
Fiber1</code> creates <code>Fiber2</code>. When <code>Fiber2</code> yields =
control, execution returns to <code>Fiber1</code>.</p>
<p>Now, let&#39;s try to do the same thing with <code>Fiber3</code>. Inside=
 <code>Fiber2</code>, we create <code>Fiber3</code>. Everything will work p=
erfectly=E2=80=94<code>Fiber3</code> will return control to <code>Fiber2</c=
ode>, and <code>Fiber2</code> will return it to <code>Fiber1</code>=E2=80=
=94this forms a hierarchy.</p>
<p>Now, imagine that we want to turn <code>Fiber1</code> into a <strong>Sch=
eduler</strong> while following these rules.<br>
To achieve this, we need to ensure that all <code>Fiber</code> instances ar=
e created from the <strong>Scheduler</strong>, so that control can always b=
e properly returned.</p><p>```php</p><p>class Scheduler {<br>=C2=A0 =C2=A0 =
private array $queue =3D [];<br><br>=C2=A0 =C2=A0 public function add(calla=
ble $task) {<br>=C2=A0 =C2=A0 =C2=A0 =C2=A0 $fiber =3D new Fiber($task);<br=
>=C2=A0 =C2=A0 =C2=A0 =C2=A0 $this-&gt;queue[] =3D $fiber;<br>=C2=A0 =C2=A0=
 }<br><br>=C2=A0 =C2=A0 public function run() {<br>=C2=A0 =C2=A0 =C2=A0 =C2=
=A0 while (!empty($this-&gt;queue)) {<br>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0=
 =C2=A0 $fiber =3D array_shift($this-&gt;queue);<br><br>=C2=A0 =C2=A0 =C2=
=A0 =C2=A0 =C2=A0 =C2=A0 if ($fiber-&gt;isSuspended()) {<br>=C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 $fiber-&gt;resume($this);<br>=C2=
=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 }<br>=C2=A0 =C2=A0 =C2=A0 =C2=A0 }<b=
r>=C2=A0 =C2=A0 }<br><br>=C2=A0 =C2=A0 public function yield() {<br>=C2=A0 =
=C2=A0 =C2=A0 =C2=A0 $fiber =3D Fiber::getCurrent();<br>=C2=A0 =C2=A0 =C2=
=A0 =C2=A0 if ($fiber) {<br>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 $this=
-&gt;queue[] =3D $fiber;<br>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 Fiber=
::suspend();<br>=C2=A0 =C2=A0 =C2=A0 =C2=A0 }<br>=C2=A0 =C2=A0 }<br>}<br><b=
r>$scheduler =3D new Scheduler();<br><br>$scheduler-&gt;add(function (Sched=
uler $scheduler) {<br>=C2=A0 =C2=A0 echo &quot;Task 1 - Step 1\n&quot;;<br>=
=C2=A0 =C2=A0 $scheduler-&gt;yield();<br>=C2=A0 =C2=A0 echo &quot;Task 1 - =
Step 2\n&quot;;<br>});<br><br>$scheduler-&gt;add(function (Scheduler $sched=
uler) {<br>=C2=A0 =C2=A0 echo &quot;Task 2 - Step 1\n&quot;;<br>=C2=A0 =C2=
=A0 $scheduler-&gt;yield();<br>=C2=A0 =C2=A0 echo &quot;Task 2 - Step 2\n&q=
uot;;<br>});<br><br>$scheduler-&gt;run();<br></p><p>```</p><p>So, to succes=
sfully switch between Fibers:</p><ol>
<li>A Fiber must return control to the <strong>Scheduler</strong>.</li>
<li>The <strong>Scheduler</strong> selects the next Fiber from the queue an=
d switches to it.</li>
<li>That Fiber then returns control back to the <strong>Scheduler</strong> =
again.</li>
</ol><p>

</p><p>This algorithm has one drawback: <strong>it requires two context swi=
tches instead of one</strong>. We could switch <strong>FiberX</strong> to <=
strong>FiberY</strong> directly.=C2=A0</p><p>Breaking the contract not only=
 disrupts the code in this RFC but also affects Revolt&#39;s functionality.=
 However, in the case of Revolt, you can say: <strong>&quot;If you use this=
 library, follow the library&#39;s contracts and do not use Fiber directly.=
&quot;</strong></p><p>
</p><p>But PHP is not just a library, it&#39;s a language that must remain =
consistent and cohesive.</p><p>&gt;<br>&gt;=C2=A0

Reading the RFC initially, I though that the Scheduler is using fibers for =
everything that runs.=C2=A0<br>&gt;</p><p>Exactly.=C2=A0=C2=A0</p><p>&gt;<b=
r>&gt;=C2=A0

You mean that when one of the fibers started by the Scheduler is starting o=
ther fibers they would usually await for them to finish, and that is a bloc=
king operating that blocks also the Scheduler?<br>&gt;</p><p>When a <strong=
>Fiber</strong> from the <strong>Scheduler</strong> decides to create anoth=
er <strong>Fiber</strong> and then tries to call blocking functions inside =
it, control can no longer return to the <strong>Scheduler</strong> from tho=
se functions.</p><p>Of course, it would be possible to track the state and =
disable the concurrency mode flag when the user manually creates a <strong>=
Fiber</strong>. But=E2=80=A6 this wouldn&#39;t lead to anything good. Not o=
nly would it complicate the code, but it would also result in a mess with d=
ifferent behavior inside and outside of <strong>Fiber</strong>.</p><p>

</p><p>This is even worse than calling <strong>startScheduler</strong>.</p>=
<p>The hierarchical switching rule is a <strong>design flaw</strong> that h=
appened because a <strong>low-level component</strong> was introduced into =
the language as part of the implementation of a <strong>higher-level compon=
ent</strong>. However, the high-level component is in <strong>User-land</st=
rong>, while the low-level component is in <strong>PHP core</strong>.</p><p=
>It&#39;s the same as implementing <code>$this</code> in OOP but requiring =
it to be explicitly passed in every method. This would lead to inconsistent=
 behavior.</p><p>

</p><p>So, this situation needs to be resolved one way or another.=C2=A0=C2=
=A0</p><p>--</p><p>Ed</p></div></div>

--000000000000eba588062fe450cd--