Make WebLocalizedString() thread-safe

https://bugs.webkit.org/show_bug.cgi?id=230954

Reviewed by Alexey Proskuryakov.

Make WebLocalizedString() thread-safe. It takes minimal effort to make it thread-safe given
that the NSBundle API is thread-safe [1] and clients keep calling it on the background thread.

[1] https://developer.apple.com/documentation/foundation/nslocalizedstringwithdefaultvalue
"As of OS X 10.11 and iOS 9, NSBundle is thread-safe. As such, you can safely call
 NSLocalizedStringWithDefaultValue from any execution context."

* Misc/WebLocalizableStrings.mm:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@283225 268f45cc-cd09-0410-ab3c-d52691b4dbfc

Author: [email protected]

Source/WebKitLegacy/mac/ChangeLog

@@ -1,3 +1,19 @@
+2021-09-29  Chris Dumez  <[email protected]>
+
+        Make WebLocalizedString() thread-safe
+        https://bugs.webkit.org/show_bug.cgi?id=230954
+
+        Reviewed by Alexey Proskuryakov.
+
+        Make WebLocalizedString() thread-safe. It takes minimal effort to make it thread-safe given
+        that the NSBundle API is thread-safe [1] and clients keep calling it on the background thread.
+
+        [1] https://developer.apple.com/documentation/foundation/nslocalizedstringwithdefaultvalue
+        "As of OS X 10.11 and iOS 9, NSBundle is thread-safe. As such, you can safely call
+         NSLocalizedStringWithDefaultValue from any execution context."
+
+        * Misc/WebLocalizableStrings.mm:
+
 2021-09-28  Chris Dumez  <[email protected]>
 
         Move Cross-Origin-Opener-Policy handling to the NetworkProcess

Source/WebKitLegacy/mac/Misc/WebLocalizableStrings.mm

@@ -37,17 +37,13 @@
 
 NSString *WebLocalizedString(WebLocalizableStringsBundle *stringsBundle, const char *key)
 {
-    // This function is not thread-safe due at least to its unguarded use of the mainBundle static variable
-    // and its use of [NSBundle localizedStringForKey:::], which is not guaranteed to be thread-safe. If
-    // we decide we need to use this on background threads, we'll need to add locking here and make sure
-    // it doesn't affect performance.
-#if !PLATFORM(IOS_FAMILY)
-    ASSERT(isMainThread());
-#endif
-
     NSBundle *bundle;
     if (stringsBundle == NULL) {
-        static NeverDestroyed<RetainPtr<NSBundle>> mainBundle = [NSBundle mainBundle];
+        static LazyNeverDestroyed<RetainPtr<NSBundle>> mainBundle;
+        static std::once_flag flag;
+        std::call_once(flag, [] () {
+            mainBundle.construct([NSBundle mainBundle]);
+        });
         ASSERT(mainBundle.get());
         bundle = mainBundle.get().get();
     } else {