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Date: Mon, 17 Nov 2025 20:39:51 +0000
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Subject: Re: [PHP-DEV] Re: PHP True Async RFC Stage 5
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From: imsop.php@rwec.co.uk ("Rowan Tommins [IMSoP]")

On 17/11/2025 09:49, Edmond Dantes wrote:
> Regarding the hybrid function-tainting model, it is designed for
> compilers or static analysis. For PHP, it could be implemented like
> this:
>
> ```php
> #NoAsync
> function myFun() {
>      asyncFun(); // Error <---
> }
>
> function asyncFun() {}
> ```
>
> This is a solvable task for static analysis.


As I understand it, Larry's suggestion was not to prevent marked code 
from calling into an async function, but to force the called function 
into sync mode.

Imagine you have code like this running PHP 8.4, using a third-party SDK 
library:

function myFun() {
     $input = someThingWithSharedState();
     $data = SomeApiSdk\someFunction($input);
     someOtherThingWithSharedState($data);
}

Then in 9.0, we get True Async, and the author of the SDK starts using 
async I/O functions somewhere deep in the library.

Without any special marking, other functions can run between the 
statements in this function, completely unknown to the author of myFun()

If you mark it as "NoAsync" in the sense you've described, a static 
analyser can point out the problem, but you still have no solution, 
short of forking the SDK and removing all async code.


Larry's "sync" marker would be a change to *run-time behaviour*: when 
myFun() begins, the scheduler switches into "linear mode", until the end 
of that function. In that mode, when a suspend() point is reached, the 
scheduler immediately resumes that coroutine rather than choosing a 
different one.

If this was marked by an attribute, you could add it to code that 
supports both PHP 8.x and 9.x, and the code would run the same in both 
versions.


Aside: I definitely think that if/when True Async is added, we should 
call the resulting version PHP 9.0 not 8.5 or 8.6 or whatever. As well 
as potentially requiring users to review code for dangerous cases, it 
would be a huge new feature worthy of the branding of a major version.


-- 
Rowan Tommins
[IMSoP]