non-volatile vs volatile reads

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non-volatile vs volatile reads

Bobrowski, Maciej

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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