volatile vs. mutable in C++

Question

I have a question about the difference between volatile and mutable. I noticed that both of the two means that it could be changed. What else? Are they the same thing? What\

Answer 1

I would like to add that volatile is also very useful when dealing with multithreading applications, i.e, you have your main thread (where main() lives) and you spawn a worker thread that will keep spinning while a variable "app_running" is true. main() controls whether "app_running" is true or false, so if you do not add the volatile attribute to the declaration of "app_running", if the compiler optimizes access to "app_running" in the code ran by the secondary thread, main() might change "app_running" to false but the secondary thread will keep running because the value has been cached. I have seen the same behavior using gcc on Linux and VisualC++. A "volatile" attribute put in "app_running" declaration solved the problem. So, this is scenario where no hardware interrupts or kernel is invoved in changing the value of such variables.