thread-safe and thread-local setlocale()

[henderkes]

It's documented at https://www.php.net/manual/en/function.setlocale.php that the setlocale php function is not thread locale (and actually, not thread safe, because the C setlocale function is MT-unsafe). This leads to very unexpected behaviour in FrankenPHP.

I would therefore like to propose changing setlocale to use POSIX uselocale instead.
Unfortunately, because querylocale is only available on BSD, this adds a lot of string caching logic to let users query for current locales, as I'm not aware of a different way. Perhaps you can give me some pointers to avoid this logic.

The logic for windows remains unchanged.

See: php/frankenphp#1941

Given the following PHP code to simulate different FrankenPHP requests:

<?php
use parallel\Runtime;

setlocale(LC_ALL,'C');
echo "main@start   : ".setlocale(LC_ALL,0)." | dp=".localeconv()['decimal_point']."\n";

$f = (new Runtime())->run(function () {
    setlocale(LC_ALL,'de_DE.UTF-8');
    echo "worker@set   : ".setlocale(LC_ALL,0)." | dp=".localeconv()['decimal_point']."\n";
});

echo "main@after   : ".setlocale(LC_ALL,0)." | dp=".localeconv()['decimal_point']."\n";

$f->value();

Currently:

[m@M bin]$ php -d "extension=/home/m/static-php-cli/buildroot/modules/parallel.so" localetest.php 
main@start   : C.UTF-8 | dp=.
worker@set   : de_DE.UTF-8 | dp=,
main@after   : de_DE.UTF-8 | dp=,

Expected, after proposed implementation:

[m@M bin]$ ./php -d "extension=/home/m/static-php-cli/buildroot/modules/parallel.so" localetest.php 
main@start   : C.UTF-8 | dp=.
worker@set   : de_DE.UTF-8 | dp=,
main@after   : C.UTF-8 | dp=.

[Girgias]

Frankly, I'd rather try to push people away from using setlocale() by recommending them to use ICU related functionality rather than relying on the OS locales behaving properly.

[Girgias]

Suggested change

	} else if (zend_string_equals_cstr(loc, ZSTR_VAL(ret_str), ZSTR_LEN(ret_str))) {
	} else if (zend_string_equals(loc, ret_str)) {

[henderkes]

I would also be fine with deprecating setlocale(), would avoid this string mess as well. I just don't believe there should be functions in a ZTS build that can crash the process.