[concurrency-interest] non-volatile vs volatile reads

Bobrowski, Maciej Maciej.Bobrowski at morganstanley.com
Thu Jun 29 09:43:23 EDT 2017


Let's consider the class:

Foo{

   int x = 0;
   volatile int y = 0;

  void write(int newVal) {
     x = newVal;
     y = newVal;
  }
}

Let's assume one writer calls write(1) , potentially multiple times.

I understand that result of calling just foo.x is not defined under JMM (it could be 0, it could be 1). However:

foo.y // this returns 1
foo.x

According to the full-fence characteristics of volatile read, foo.x is guaranteed to be 1. How is this achieved? Let's assume x is on a different cache-line or is stored in local registers?


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