1948601 - Enable more types for the use with Atomic<T>

Status: NEW

(Core :: MFBT, enhancement)

Description

[Jens Stutte [:jstutte]]

Currently we can only use booleans, integral types and enums (all only of size 4 or 8) with Atomic<T>. The underlying std::atomic has less strict requirements.

I assume we could just use the same minimal set of functions as for enums, something like:

 /**
- * Atomic<T> implementation for enum types.
+ * Atomic<T> implementation for other types.
  *
  * The atomic store and load operations and the atomic swap method is provided.
  */
 template <typename T, MemoryOrdering Order>
-class Atomic<T, Order, std::enable_if_t<std::is_enum_v<T>>>
+class Atomic<
+    T, Order,
+    std::enable_if_t<
+        !std::is_integral_v<T> && !std::is_same_v<T, bool> &&
+        !std::is_pointer_v<T> &&
+        // See https://en.cppreference.com/w/cpp/atomic/atomic for constraints.
+        std::is_trivially_copyable_v<T> && std::is_copy_constructible_v<T> &&
+        std::is_move_constructible_v<T> && std::is_copy_assignable_v<T> &&
+        std::is_move_assignable_v<T> &&
+        std::is_same_v<T, typename std::remove_cv<T>::type>>>
     : public detail::AtomicBase<T, Order> {
   typedef typename detail::AtomicBase<T, Order> Base;
 
  public:
   constexpr Atomic() : Base() {}
   explicit constexpr Atomic(T aInit) : Base(aInit) {}
 
   operator T() const { return T(Base::Intrinsics::load(Base::mValue)); }

to enable its use for more types. There might be also a question about the allowed size of types, but that could be a bit more tricky to understand.

Comment 1

[Jens Stutte [:jstutte]]

This came up in bug 1920451 when trying to use Atomic<std::chrono::time_point<...>>.

Bug 732043 long list of comments (from 12 years ago) might give some background on the rationales for the current restrictions.