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Multiple ChoiceIntermediate 45s

Double-Checked Locking with Atomics

To make double-checked locking correct in C++11+, the shared pointer must be:
Options
  1. 1A plain T* qualified volatile, which stops the compiler caching it
  2. 2A static local pointer written with no synchronization at all
  3. 3Protected by a recursive_mutex that both checks acquire on entry
  4. 4std::atomic<T*> with acquire/release (or std::call_once/once_flag)
dclpatomicssingleton

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