[libcxx-commits] [libcxx] [libc++] Speed up classic locale (PR #72112)

[Dmitry Vyukov via libcxx-commits]

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@@ -538,16 +543,31 @@ locale::__imp::use_facet(long id) const
 
 // locale
 
+std::atomic<locale::__imp*> locale::__imp::classic_;
+
 const locale&
 locale::__imp::make_classic()
 {
     // only one thread can get in here and it only gets in once
     alignas(locale) static std::byte buf[sizeof(locale)];
     locale* c = reinterpret_cast<locale*>(&buf);
     c->__locale_ = &make<__imp>(1u);
+    classic_.store(c->__locale_, std::memory_order_relaxed);
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dvyukov wrote:

Added a comment explaining why relaxed ordering is the right one.

https://github.com/llvm/llvm-project/pull/72112