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Subject: Re: [PHP-DEV] Switching max_execution_time from CPU time to
 wall-clock time and from SIGPROF to SIGALRM
In-Reply-To: <CAP1Jc10EHNhfCwz9p0tSyrSLiskCFnz7Ae0aTtYFJ8snYmVNOQ@mail.gmail.com>
Date: Fri, 17 May 2024 14:42:07 -0300
Cc: PHP internals <internals@lists.php.net>
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Message-ID: <D474A4F3-16A8-492A-B76C-E240A3712DC9@cmpct.info>
References: <CAP1Jc10EHNhfCwz9p0tSyrSLiskCFnz7Ae0aTtYFJ8snYmVNOQ@mail.gmail.com>
To: Arnaud Le Blanc <arnaud.lb@gmail.com>
From: calvin@cmpct.info (Calvin Buckley)

On May 17, 2024, at 10:47=E2=80=AFAM, Arnaud Le Blanc =
<arnaud.lb@gmail.com> wrote:
>=20
> Hi internals,
>=20
> There is an issue with max_execution_time on MacOS, probably only
> MacOS 14 on Apple Silicon, that causes timeouts to fire too early [1].
> max_execution_time is implemented with setitimer(ITIMER_PROF) on this
> platform, and the SIGPROF signal is delivered too early for some
> reason. Switching to ITIMER_REAL appears to fix the issue, and Manuel
> Kress opened a PR [3].
>=20
> Are there objections against switching to ITIMER_REAL on MacOS (Apple
> Silicon only) in all currently supported PHP versions? (next 8.2.x,
> 8.3.x, 8.x)
>=20
> Apart from fixing the issue, this would introduce the following minor
> breaking changes:
>=20
> - max_execution_time on MacOS would be based on wall-clock time rather
> than CPU time, so the time spent in I/O, sleep(), and syscalls in
> general would count towards the max_execution_time
> - The SIGALRM signal would be used instead of the SIGPROF signal
> (using SIGALRM conflicts with pcntl_alarm(), but SIGPROF conflicts
> with profilers). As noted by Dmitry, it also conflicts with sleep() on
> some platforms, however this should be safe on MacOS.
>=20
> Currently max_execution_time is based on wall-clock time on ZTS and
> Windows, and CPU time otherwise. On Linux and FreeBSD, wall-clock time
> can also be used when building with
> --enable-zend-max-execution-timers. M=C3=A1t=C3=A9 proposed to add a =
wall-clock
> based timeout in the past [2] but the discussion has stalled. Any
> thoughts about eventually switching other platforms to wall-clock
> timeouts in the next 8.x ?
>=20
> TL;DR:
> - Any objection about using wall-clock max_execution_time and SIGALRM
> on MacOS Apple Silicon in all supported versions?
> - Thoughts about using wall-clock timeouts on all platforms in the =
next 8.x ?
>=20
> [1] https://github.com/php/php-src/issues/12814
> [2] https://github.com/php/php-src/pull/6504
> [3] https://github.com/php/php-src/pull/13567
>=20
> Best Regards,
> Arnaud

FWIW, Cygwin and IBM i are also using wall time, because these platforms
don't do execution time. IIRC, the difference between platforms with how
max_execution_time is counted doesn't seem to be documented last I =
checked.=