Is processor cache flushed during context switch in multicore?

Question

Recently, I discussed why there is a volatile mark at seq in Java Actors demo

@volatile private var seq = 0L
private def nextSeq: Long = {
  val next = seq
          


        

Answer 1

Whenever there is any sort of context switch the OS will save its state such that it can be restarted again on any core (assuming it has not been tied to a specific core using a processor affinity function).

Saving a state that for some reason or other is incomplete defeats the entire purpose of threading or processing, therefore the caches are flushed as part of the switch.

Volatile has nothing whatsover to do with context switching. It merely tells the compiler that the memory location is subject to change without notice and therefore must be accessed each time the source code dictates it i e the usual compiler behaviour of optimizing accesses to memory locations does not apply to the volatile-declared location.