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Date: Sun, 23 Nov 2025 21:53:21 +0000
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Subject: Re: [PHP-DEV] [VOTE] True Async RFC 1.6
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From: imsop.php@rwec.co.uk ("Rowan Tommins [IMSoP]")

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On 23/11/2025 19:09, Edmond Dantes wrote:
>> @Ed Unless something calls `spawn` all I/O is going to be blocking &
>> non-concurrent, correct?
> Yes.
> If no one calls spawn, this is equivalent to the code running inside a
> single coroutine.
>
> At the moment, TrueAsync has an internal flag that allows it to be
> enabled or disabled. If Async is disabled, an exception will be
> thrown.


I think there's a lot of confusion in this thread because different 
people are talking about different scenarios. Perhaps it would be useful 
to introduce some User Stories...


Async Alice is working on a brand new application written in PHP 9, and 
is designing it from the ground up to make use of async capabilities 
wherever possible. She wants third-party libraries to use async I/O so 
that she can use them in her design.

Beginner Bob has a recently built application, and thinks there's an 
opportunity to improve it with async I/O, but doesn't know anything 
about it. He wants a simple-to-use API that lets him get the benefits, 
and clear instructions on what pitfalls to look out for.

Legacy Les is maintaining a 20-year-old business back office system, 
which makes extensive use of global state and does not have good 
automated testing. He wants to run it under PHP 9, and to use up-to-date 
third-party libraries for new functionality, without an expensive and 
risky rewrite of existing code.

Finally, SDK Susie is publishing the official PHP library for a popular 
cloud API. She wants to serve the best version she can for Alice, Bob, 
and Les, but doesn't want to maintain separate "sync" and "async" 
branches of the library or its methods.

Feel free to create more personas if you want to talk about additional 
scenarios.


The first thing I want to clarify is that SDK Susie doesn't necessarily 
need to change the public methods of her library; she can still use 
async I/O internally. For instance, if a method already returns an 
Iterator to silently fetch a page of results at a time, that can be 
changed to store Promises internally, and await them when the data is 
needed.

However, she might want to mark it as a breaking change anyway, so 
that Async Alice and Beginner Bob know they are opting into it.


Legacy Les won't get it until he opts in, but at some point he will need 
a new version of the library for other reasons (e.g. because the cloud 
API becomes incompatible with the old library version); so he still 
needs a way to run it safely.

If he runs PHP in a mode where any attempt to use async I/O *throws an 
error*, he still can't use the new version of the library, so this 
doesn't help him.


However, if Legacy Les can run PHP in a mode where any attempt to use 
async I/O is *automatically run synchronously*, then he will be happy: 
he can run his legacy application under PHP 9, and use the updated 
library, without worrying about async code.

Beginner Bob doesn't want to run his whole application in "sync only" 
mode, but might want to switch *parts of it*, so that he doesn't have to 
think about them yet. So a scoped, rather than global, switch might be 
useful for him.


This is how I picture that mode working: when SDK Susie's library code 
calls "spawn", a Coroutine is created as normal. However, when it 
suspends, the Scheduler immediately resumes it, rather than switching to 
a different Coroutine. The library code will see the Coroutine object it 
expects, but passing it to "await" will immediately produce its result.

However, I might well be misunderstanding something, and this is either 
impossible or difficult to implement. If so, I think some other solution 
to Legacy Les's requirements is needed.


I hope this description is useful.


-- 
Rowan Tommins
[IMSoP]

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    <div class="moz-cite-prefix">On 23/11/2025 19:09, Edmond Dantes
      wrote:<br>
    </div>
    <blockquote type="cite"
cite="mid:CAMW7n8DM4MCP25gSLBbd3+Awzs2+p6Qs_jPgx1mk=RjSVe+iUw@mail.gmail.com">
      <pre class="moz-quote-pre" wrap=""><blockquote type="cite"
      style="color: #007cff;"><pre wrap="" class="moz-quote-pre">@Ed Unless something calls `spawn` all I/O is going to be blocking &amp;
non-concurrent, correct?
</pre></blockquote><pre wrap="" class="moz-quote-pre">Yes.
If no one calls spawn, this is equivalent to the code running inside a
single coroutine.

At the moment, TrueAsync has an internal flag that allows it to be
enabled or disabled. If Async is disabled, an exception will be
thrown.</pre></pre>
    </blockquote>
    <p><br>
    </p>
    <p>I think there's a lot of confusion in this thread because
      different people are talking about different scenarios. Perhaps it
      would be useful to introduce some User Stories...</p>
    <p><br>
    </p>
    <p>Async Alice is working on a brand new application written in PHP
      9, and is designing it from the ground up to make use of async
      capabilities wherever possible. She wants third-party libraries to
      use async I/O so that she can use them in her design.</p>
    <p>Beginner Bob has a recently built application, and thinks there's
      an opportunity to improve it with async I/O, but doesn't know
      anything about it. He wants a simple-to-use API that lets him get
      the benefits, and clear instructions on what pitfalls to look out
      for.</p>
    <p>Legacy Les is maintaining a 20-year-old business back office
      system, which makes extensive use of global state and does not
      have good automated testing. He wants to run it under PHP 9, and
      to use up-to-date third-party libraries for new functionality,
      without an expensive and risky rewrite of existing code.</p>
    <p>Finally, SDK Susie is publishing the official PHP library for a
      popular cloud API. She wants to serve the best version she can for
      Alice, Bob, and Les, but doesn't want to maintain separate "sync"
      and "async" branches of the library or its methods.</p>
    <p>Feel free to create more personas if you want to talk about
      additional scenarios.</p>
    <p><br>
    </p>
    <p>The first thing I want to clarify is that SDK Susie doesn't
      necessarily need to change the public methods of her library; she
      can still use async I/O internally. For instance, if a method
      already returns an Iterator to silently fetch a page of results at
      a time, that can be changed to store Promises internally, and
      await them when the data is needed.</p>
    <p>However, she might want to mark it as a breaking change anyway,
      so that Async Alice and Beginner Bob know they are opting into it.</p>
    <p><br>
    </p>
    <p>Legacy Les won't get it until he opts in, but at some point he
      will need a new version of the library for other reasons (e.g.
      because the cloud API becomes incompatible with the old library
      version); so he still needs a way to run it safely.</p>
    <p>If he runs PHP in a mode where any attempt to use async I/O
      *throws an error*, he still can't use the new version of the
      library, so this doesn't help him.</p>
    <p><br>
    </p>
    <p>However, if Legacy Les can run PHP in a mode where any attempt to
      use async I/O is *automatically run synchronously*, then he will
      be happy: he can run his legacy application under PHP 9, and use
      the updated library, without worrying about async code.</p>
    <p>Beginner Bob doesn't want to run his whole application in "sync
      only" mode, but might want to switch *parts of it*, so that he
      doesn't have to think about them yet. So a scoped, rather than
      global, switch might be useful for him.</p>
    <p><br>
    </p>
    <p>This is how I picture that mode working: when SDK Susie's library
      code calls "spawn", a Coroutine is created as normal. However,
      when it suspends, the Scheduler immediately resumes it, rather
      than switching to a different Coroutine. The library code will see
      the Coroutine object it expects, but passing it to "await" will
      immediately produce its result.</p>
    <p>However, I might well be misunderstanding something, and this is
      either impossible or difficult to implement. If so, I think some
      other solution to Legacy Les's requirements is needed.</p>
    <p><br>
    </p>
    <p>I hope this description is useful.</p>
    <p><br>
    </p>
    <pre class="moz-signature" cols="72">-- 
Rowan Tommins
[IMSoP]</pre>
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