Volatile in its current implementation is not broken despite popular blog posts claiming such a thing. It is however badly specified and the idea of using a modifier on a field to specify memory ordering is not that great (compare volatile in Java/C# to C++’s atomic specification that had enough time to learn from the … Read more
The statement “the value can be changed by means outside of this code” basically means that another program or hardware can update that variable. This is totally possible. One way of thinking of this is by relating this concept to a file that is shared among multiple programs. A file can be opened, written, and … Read more
This is sort of a side note explanation on some of the details of volatile. Writing this here because it is too much for an comment. I want to give some examples which show how volatile affects visibility, and how that changed in jdk 1.5. Given the following example code: public class MyClass { private … Read more
I know how to stop it from happening I just don’t know why it causes it (yet). And it would appear you have indeed found a bug either in the .Net BCL or, more likely, in the JIT. I just commented out all the lines in the MyButton_Click_Aux method and then started bringing them back … Read more
Whether it is optimized out depends entirely on compilers and what they choose to optimize away. The C++98/03 memory model does not recognize the possibility that x could change between the setting of it and the retrieval of the value. The C++11 memory model does recognize that x could be changed. However, it doesn’t care. … Read more
Is the compiler free to cache the value of the atomic variable and unroll the loop? The compiler cannot cache the value of an atomic variable. However, since you are using std::memory_order_relaxed, that means the compiler is free to reorder loads and stores from/to this atomic variable with regards to other loads and stores. Also … Read more
register volatile int T=10; volatile qualifier means that the compiler cannot apply optimizations or reorder access to T, While register is a hint to the compiler that T will be heavily used. If address of T is taken, the hint is simply ignored by the compiler. Note that register is deprecated but still used. Practical … Read more
Yes, volatile is required, and the right declaration is: volatile unsigned char *my_data; This declares my_data to be a pointer to volatile unsigned char. To make the pointer itself volatile, you’d need this instead: unsigned char *volatile my_data; And of course, both the pointer and the pointed-to data may be volatile: volatile unsigned char *volatile … Read more
The atomic objects make use of Compare and Swap mechanism to make them atomic – i.e. it is possible to guarantee that the value was as specified and is now at the new value. The code you posted continually tries to set the current value to one more than it was before. Remember that another … Read more
c They will not be reordered. C17 6.5.2.3(3) says: A postfix expression followed by the . operator and an identifier designates a member of a structure or union object. The value is that of the named member, 97) and is an lvalue if the first expression is an lvalue. If the first expression has qualified … Read more