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Subject: Re: [PHP-DEV] [RFC] Add num_available_processors
In-Reply-To: <a1509633-ad50-4779-bc46-0f782cd8b7c5@app.fastmail.com>
Date: Sun, 25 May 2025 12:07:50 +0200
Cc: PHP Internals <internals@lists.php.net>
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Message-ID: <60B4033B-2E6A-4157-A698-6C58454B07C9@garsi.de>
References: <bc1ec15125844c78a6aa23dce6148af9@danielkesselberg.de>
 <a1509633-ad50-4779-bc46-0f782cd8b7c5@app.fastmail.com>
To: Daniel Kesselberg <mail@danielkesselberg.de>,
 Rob Landers <rob@bottled.codes>
From: alwin@garsi.de (Alwin Garside)

On 24 May 2025, at 20:48, Rob Landers <rob@bottled.codes> wrote:
>=20
> On Sat, May 24, 2025, at 19:37, Daniel Kesselberg wrote:
>>=20
>>=20
>> Hi everyone,
>>=20
>> I'm happy to share my first RFC :) It proposes adding a small =
function=20
>> to retrieve the number of available processors; a feature that's=20
>> commonly found in other programming languages and one that I believe=20=

>> would be a useful addition to PHP.
>>=20
>> The related PR has already received a bit of early traction, and now=20=

>> that the RFC is complete, I'm looking forward to your feedback!
>>=20
>> RFC: https://wiki.php.net/RFC/num_available_processors
>> Patch: https://github.com/php/php-src/pull/11137
>>=20
>> Best
>> Daniel
>>=20
>=20
> Looks good!
>=20
> My main question is: what is this actually counting? In the RFC it =
mentions "available processing units" ... which means, what? What counts =
as a "processing unit"? Are we talking about CPU Threads/cores; NPU =
cores; TPM cores; clocks? GPS? GPU? ... a modern computer has many =
"processing units" for different purposes and workloads. I=E2=80=99m =
assuming this is CPU Threads, not physical cores? I will refer to CPU =
Threads as "Logical Cores" so we all don=E2=80=99t get confused since =
most of us here are programmers and saying "thread" has a different =
meaning.
>=20
> Secondly, how is it counting "available"? If I assign PHP to a =
specific CPU affinity mask (say one logical core), will it return 1, or =
the total number of logical cores available on my machine? I would =
expect it to be 1, since PHP only has access to 1, but I can also see =
the logic in returning the total number.
>=20
> =E2=80=94 Rob


Hi Daniel,

I agree with Rob that "processor" is a bit too ambiguous. I'd use the =
phrase "cpu_core" instead. Yes, technically that's not entirely accurate =
when hyper-threading is used, but in most cases it's not trivial to =
distinguish physical cores from logical cores anyway, and "cpu_cores" =
provides the most understandable abstraction for the vast majority of =
use cases: deciding how many parallel processes one should use for =
optimal use of the CPU.

Also, is it really necessary to add "available" as a disambiguator? In =
other words: are there future plans to add a function that provides the =
"total" or "unavailable" number of processors? If not, I'd just drop the =
"available" part.

Finally, from a quick search in php-src there doesn't seem to be any =
existing function name that starts with `num_`. For the sake of =
consistency with the existing PHP functions, and similar functionality =
in other languages, I suggest suffixing the function name with `_count` =
instead.

So, to wrap this all up, I'd like to respectfully propose the following =
function name instead:

    cpu_core_count()

Alwin=