What is the “volatile” keyword used for?

Question

I read some articles about the volatile keyword but I could not figure out its correct usage. Could you please tell me what it should be used for in C# and in

Answer 1

In Java, "volatile" is used to tell the JVM that the variable may be used by multiple threads at the same time, so certain common optimizations cannot be applied.

Notably the situation where the two threads accessing the same variable are running on separate CPU's in the same machine. It is very common for CPU's to cache aggressively the data it holds because memory access is very much slower than cache access. This means that if the data is updated in CPU1 it must immediately go through all caches and to main memory instead of when the cache decides to clear itself, so that CPU2 can see the updated value (again by disregarding all caches on the way).