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Date: Fri, 17 May 2024 15:47:03 +0200
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Subject: [PHP-DEV] Switching max_execution_time from CPU time to wall-clock time and from SIGPROF to SIGALRM
To: PHP internals <internals@lists.php.net>
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From: arnaud.lb@gmail.com (Arnaud Le Blanc)

Hi internals,

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].

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)

Apart from fixing the issue, this would introduce the following minor
breaking changes:

- 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.

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-c=
lock
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 ?

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=
 ?

[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

Best Regards,
Arnaud