Incorrect use of the release fence in Singleton::Ref

[Komfr]

Both the last released version 8.7 and the current master branch (2038ab1) have an incorrect order of the release fence and pointer store operations when creating the object.

The current current code is

T *newObject = m_objectFactory();
s_pObject.store(newObject, std::memory_order_relaxed);
std::atomic_thread_fence(std::memory_order_release);

however the correct sequence, which is also described in the article linked from the function documentation, should be

T *newObject = m_objectFactory();
std::atomic_thread_fence(std::memory_order_release);
s_pObject.store(newObject, std::memory_order_relaxed);

Otherwise there is no guarantee that the object content will be already fully stored in the memory when another thread might see the pointer and attempt to access it.

[noloader]

Thanks @Komfr,

This should be cleared at Commit a23f78d116c9.

We just released Crypto++ 8.8, so this change should get good testing coverage before the next release.