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Date: Sat, 15 Nov 2025 16:41:11 +0200
Message-ID: <CAMW7n8AX7O7x99KGdPSai6sPP1Xd6V4ojQ7CEWmxthNLPM2hyQ@mail.gmail.com>
Subject: Re: [PHP-DEV] Re: PHP True Async RFC Stage 5
To: Rob Landers <rob@bottled.codes>
Cc: php internals <internals@lists.php.net>, Jakub Zelenka <bukka@php.net>, 
	Larry Garfield <larry@garfieldtech.com>
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From: edmond.ht@gmail.com (Edmond Dantes)

Hello.

> Based on the conversation so far, I=E2=80=99d imagine the list to look so=
mething like:

Yes, that=E2=80=99s absolutely correct. When a programmer uses an operation
that would normally block the entire thread, control is handed over to
the Scheduler instead.
The suspend function is called inside all of these operations.

> If that=E2=80=99s the intended model, it=E2=80=99d help to have that spel=
led out directly; it makes it immediately clear which functions can or will=
 suspend and prevents surprises.

In the Async implementation, it will be specified which functions are suppo=
rted.

> I also think the RFC needs at least minimal wording about scheduler guara=
ntees, even if the details are implementation-specific.
The Scheduler guarantees that a coroutine will be invoked if it is in the q=
ueue.

>  For example, is the scheduler run-to-suspend? FIFO or round-robin wakeup=
? And non-preemptive behaviour only appears here in the thread. It isn=E2=
=80=99t mentioned in the RFC itself.

In Go, for example, when it was still cooperative, these details were
also not part of any public contract. The only guarantee Go provided
was that a coroutine would not be interrupted arbitrarily. The same
applies to this RFC: coroutines are interrupted only at designated
suspension points.
However, neither Go nor any other language exposes the internal
details of the Scheduler as part of a public contract, because those
details may change without notice.

> That=E2=80=99s important for people writing long, CPU-bound loops, since =
nothing will interrupt them unless they explicitly yield.
Hypothetically, in the future it may become possible to interrupt
loops, just like Go eventually did. This would likely require an
additional RFC. PHP does have the ability to interrupt a loop at any
point, but most likely only for terminating execution.
This RFC does nothing of the sort.

> Lastly, cancellation during a syscall is still unclear. If a coroutine is=
 cancelled while something like fwrite() or a DB write is in progress, what=
 should happen?
> Does fwrite() still return the number of bytes written? Does it throw? Fo=
r write-operations in particular, this affects whether applications can mai=
ntain a consistent state.

If the write operation is interrupted, the function will return an
error according to its contract. In this case, it will return false.

> Clarifying these points would really help people understand how to reason=
 about concurrency with this API.

This is described in the document.
There is, of course, a nuance regarding extended error descriptions,
but at the moment no such changes are planned.