I think we should remove getHardwareConcurrency and use a sane default.

A hint for preview_concurrency_all and preview_concurrency_new at https://docs.nextcloud.com/server/latest/admin_manual/installation/server_tuning.html would be nice.

Every time a generator instance is loaded, we fetch /proc/cpuinfo to use the number of processor as default value. I think this is unnecessary.

We don't support FreeBSD. But TrueNAS which is based on FreeBSD. On FreeBSD /proc/cpuinfo is not available. We need a different way to retrieve the processors: https://github.com/nextcloud/serverinfo/blob/1146b21d13073c5e8799eb707096d12b5f682026/lib/OperatingSystems/FreeBSD.php#L81

My recommendation is to keep it simple.

This whole section of code getHardwareConcurrency() is semi-irrelevant anyhow since there are defaults defined and the admin can also define the best (preferred) parameters via preview_concurrency_* already. This is just fallback code and shouldn't be getting executed every time.

The overall generator CPU balancing feature is sound, but the code elsewhere within it could use some refactoring.

The only reason the open_basedir trigger in this issue can't easily be headed off by the admin simply configuring the preview_concurrency_* settings is because of the order of operations the fallback is implemented in.

I also wouldn't bother with trying to process the contents of the open_basedir if it's found. I'd just fall back to the sane defaults (which the admin can still override if they wish as currently coded). Plus even after parsing open_basedir the processing of /proc could still fail for other reasons (like different OSes as @kesselb noted).

That said, K.I.S.S. - and rather than submitting a competing PR - here's the quick and dirty path I suggest until a more extensive refactor can happen:

joshtrichards@30c5f24

I agree that simplication is (almost) ALWAYS the way to go, but this PR is only about open_basedir error suppression, nothing more. Feel free to submit a proper PR to simplify the whole thing or complete the actual checks for all OSes.

Could this work?:

public static function getHardwareConcurrency(): int {
static $width;
if (!isset($width)) {
if (function_exists('nproc')) {
// 'nproc' function is available, use it to determine the hardware concurrency
$width = (int) nproc();
} elseif (strtoupper(substr(PHP_OS, 0, 3)) === 'LIN') {
// Use 'sysctl' to query the number of CPU cores on Linux
$result = shell_exec('sysctl -n hw.ncpu');
if ($result !== null) {
$width = (int) trim($result);
} else {
$width = 0; // Handle the case when 'sysctl' is not available or fails.
}
} else {
// Handle other platforms or cases
$width = 0;
}
}
return $width;
}

This first checks if the nproc function is available. If it is, it uses nproc to determine the hardware concurrency. If nproc is not available and the operating system is Linux, it uses the sysctl approach to query the number of CPU cores. If neither method is available or if the code is running on a platform other than Linux, it sets the hardware concurrency to 0.

Just my ¢2

/backport to stable27