Scott Meyers - Effective Modern C++

You'll find a nice treatment in Anthony Williams' C++ Concurrency in Action (Manning Publications, 2012), section 9.2.

Item 39explains that the kind of communications channel associated with a future can be employed for other purposes. For this Item, however, we'll consider only its use as a mechanism for a callee to convey its result to a caller.

A reasonable place to begin researching the matter is my 24 December 2013 blog post at The View From Aristeia, "ThreadRAII + Thread Suspension = Trouble?"

This is true only for std::atomics using sequential consistency , which is both the default and the only consistency model for std::atomicobjects that use the syntax shown in this book. C++11 also supports consistency models with more flexible code-reordering rules. Such weak (aka relaxed ) models make it possible to create software that runs faster on some hardware architectures, but the use of such models yields software that is much more difficult to get right, to understand, and to maintain. Subtle errors in code using relaxed atomics is not uncommon, even for experts, so you should stick to sequential consistency if at all possible.

y's type is auto-deduced, so it uses the rules described in Item 2. Those rules dictate that for the declaration of non-reference non-pointer types (which is the case for y), constand volatilequalifiers are dropped. y's type is therefore simply int. This means that redundant reads of and writes to ycan be eliminated. In the example, compilers must perform both the initialization of and the assignment to y, because xis volatile, so the second read of xmight yield a different value from the first one.

In this Item, to “copy” a parameter generally means to use it as the source of a copy or move operation. Recall on page 2 that C++ has no terminology to distinguish a copy made by a copy operation from one made by a move operation.

Sentences like this are why it'd be nice to have terminology that distinguishes copies made via copy operations from copies made via move operations.