Fix GH-12778: Windows IIS FastCGI Spin-Up Performance Slowdown

The issue isn't limited to Windows only, I can also see the slowdown on
my Linux machine. The cause of the slowdown is 26e4244. In that
commit a locale reset routine was implemented that gets called on
startup.
The fix from that commit is only necessary when using readline
functionality, there are three places that is used:
  - phpdbg
  - with readline_cli
  - readline() php function
So we make sure we only reset the locale when one of these is used,
preventing the overhead on normal website-serving use-cases.

Author: nielsdos

UPGRADING.INTERNALS

@@ -63,3 +63,11 @@ PHP 8.4 INTERNALS UPGRADE NOTES
 ========================
 5. SAPI changes
 ========================
+
+* The LC_CTYPE locale is no longer overridden at module startup to C.UTF-8.
+  This was originally introduced to fix an issue with UTF-8 characters when
+  libedit was used for providing the readline functionality. The new fix now
+  delays the locale reset until the readline functionality is actually used.
+  SAPIs relying on this behaviour must manually call zend_reset_lc_ctype_locale().
+  This change is done to fix a performance regression.
+  See https://github.com/php/php-src/pull/12784.

ext/readline/readline.c

@@ -115,6 +115,15 @@ PHP_MINFO_FUNCTION(readline)
 
 /* }}} */
 
+static void php_readline_fix_locale() {
+	/* Yes, this variable is process-wide, but so is the locale setting. */
+	static bool locale_fixed = false;
+	if (!locale_fixed) {
+		locale_fixed = true;
+		zend_reset_lc_ctype_locale();
+	}
+}
+
 /* {{{ Reads a line */
 PHP_FUNCTION(readline)
 {
@@ -126,6 +135,8 @@ PHP_FUNCTION(readline)
 		RETURN_THROWS();
 	}
 
+	php_readline_fix_locale();
+
 	result = readline(prompt);
 
 	if (! result) {

ext/readline/readline_cli.c

@@ -634,6 +634,8 @@ static int readline_shell_run(void) /* {{{ */
 #endif
 	read_history(history_file);
 
+	zend_reset_lc_ctype_locale();
+
 	EG(exit_status) = 0;
 	while ((line = readline(ZSTR_VAL(prompt))) != NULL) {
 		if (strcmp(line, "exit") == 0 || strcmp(line, "quit") == 0) {

main/main.c

@@ -2104,7 +2104,6 @@ zend_result php_module_startup(sapi_module_struct *sf, zend_module_entry *additi
 	zuf.getenv_function = sapi_getenv;
 	zuf.resolve_path_function = php_resolve_path_for_zend;
 	zend_startup(&zuf);
-	zend_reset_lc_ctype_locale();
 	zend_update_current_locale();
 
 	zend_observer_startup();

sapi/phpdbg/phpdbg.c

@@ -1356,6 +1356,8 @@ int main(int argc, char **argv) /* {{{ */
 	PHPDBG_G(flags) = flags;
 
 	if (phpdbg->startup(phpdbg) == SUCCESS) {
+		zend_reset_lc_ctype_locale();
+
 		zend_mm_heap *mm_heap;
 #ifdef _WIN32
 	EXCEPTION_POINTERS *xp;