Reading the (ISO 9899:2018) standard literally, then it is undefined behavior. C17 5.1.2.3/2 – definition of side effects: Accessing a volatile object, modifying an object, modifying a file, or calling a function that does any of those operations are all side effects C17 6.5/2 – sequencing of operands: If a side effect on a scalar … Read more
No, you will never get a NPE. This is because volatile also has the memory-effect of introducing a happens-before relationship. In other words, it will prevent reordering of a = one; b = two; The statements above, will not be re-ordered, and all threads will observe value one for a if b already has value … Read more
In your example, the two are the same. But the issues revolve around pointers. First off, volatile uint8_t *foo; tells the compiler the memory being pointed to is volatile. If you want to mark the pointer itself as volatile, you would need to do uint8_t * volatile foo; And that is where you get to … Read more
The volatile keyword is used to declare an array type of a function parameter. Here, double x[volatile] is equivalent to double * volatile x. The cppreference says : In a function declaration, the keyword volatile may appear inside the square brackets that are used to declare an array type of a function parameter. It qualifies … Read more
You should really check out this article: http://brooker.co.za/blog/2012/09/10/volatile.html. The blog article argues volatile reads can be a lot slower (also for x86) than non-volatile reads on x86. Test 1 is a parallel read and write to a non-volatile variable. There is no visibility mechanism and the results of the reads are potentially stale. Test 2 … Read more
You are not doing anything wrong. According to the documentation: A volatile field should not normally be passed using a ref or out parameter, since it will not be treated as volatile within the scope of the function. There are exceptions to this, such as when calling an interlocked API.
The volatile prevents memory writes from being re-ordered, making it impossible for other threads to read uninitialized fields of your singleton through the singleton’s pointer. Consider this situation: thread A discovers that uniqueInstance == null, locks, confirms that it’s still null, and calls singleton’s constructor. The constructor makes a write into member XYZ inside Singleton, … Read more
He’s implying that a processor-specific detail should not show up to a person using a framework that “abstracts” details like that away from the programmer. If you are using low-lock techniques like volatile fields, explicit memory barriers, and the like, then you are entirely in the world of processor-specific details. You need to understand at … Read more
Marking a member function volatile is like marking it const; it means that the receiver object is treated as though it were declared as a volatile T*. Consequentially, any reference to x or y will be treated as a volatile read in the member function. Moreover, a volatile object can only call volatile member functions. … Read more
Use const_cast. For example, volatile sample *pvs = new sample(); sample *ps = const_cast<sample*>(pvs); //casting away the volatile-ness That is, const_cast is used to cast away both const-ness as well as volatile-ness. Unfortunately, its name doesn’t contain the term “volatile”. Maybe, that is because the keyword const is more common in use than the keyword … Read more