i = 1 always happens-before v = 2 True. By JLS section 17.4.5, If x and y are actions of the same thread and x comes before y in program order, then hb(x, y). v = 2 happens-before vDst = v in JMM only if it’s actually happens before in time i = 1 happens-before …
Firmware developer here. This is a standard problem in embedded programming, and one that trips up many (even very experienced) developers. My assumption is that you are attempting to access a hardware register, and that register value can change over time (be it interrupt status, timer, GPIO indications, etc.). The volatile keyword is only part …
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 …
There’s a good talk by the C++ committee language evolution chair on why. Brief summary, the places that volatile is being removed from didn’t have any well defined meaning in the standard and just caused confusion. Motivating (Ambiguous) Examples Volatile bit Fields should be specified by your hardware manual and/or compiler. Is += a single/atomic …
Consider this code, int some_int = 100; while(some_int == 100) { //your code } When this program gets compiled, the compiler may optimize this code, if it finds that the program never ever makes any attempt to change the value of some_int, so it may be tempted to optimize the while loop by changing it …
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 …
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 …
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 …
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.
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 …