Gtjkyu

Can two stores be reordered in such singleton implementation? In the following singleton 'get' function, can other threads see instance as not-null, but almost_done still false? (Say almost_done is initially false .) instance almost_done almost_done false Singleton *Singleton::Get() { auto tmp = instance.load(std::memory_order_relaxed); std::atomic_thread_fence(std::memory_order_acquire); if (tmp == nullptr) { std::lock_guard<std::mutex> guard(lock); tmp = instance.load(std::memory_order_relaxed); if (tmp == nullptr) { tmp = new Singleton(); almost_done.store(true, std::memory_order_relaxed); // 1 std::atomic_thread_fence(std::memory_order_release); instance.store(tmp, std::memory_order_relaxed); // 2 } } return tmp; } If they can, why? What's the rationale? I know nothing can "get out" of an acquire-release section, but can't 2 enter it and be reorder...

Atomicness for a global variable shared by threads Okay, trivial question. Problem is, every answer I find on here has 3/4 conflicting answers. I have a very simple problem. I have a global variable called ABORT_SIGNAL. As of now, this is declared volatile int ABORT_SIGNAL . I understand that this does not do what I wish... which is... volatile int ABORT_SIGNAL I have two threads which may write to ABORT_SIGNAL. It will start at 0, and go to 1 after a number of seconds. Every other thread will be reading this variable on a regular basis, checking to see if the value has been set to 1. Would the following achieve this .... #include <stdint.h> atomic_int ABORT_SIGNAL; ... // When updating the value ... atomic_store(&ABORT_SIGNAL, someValue); // When reading the value ... if (atomic_load_explicit(&ABORT_SIGNAL, memory_order_relaxed)) doSomething() Others have also suggested that I would need to do something like the following. After each write issue atomic_thread_fence(m...