Re: Can you use "synchronized" for data members

On Wed, 9 Nov 2011, markspace wrote:


Yes. Although it isn't *quite* the same thing.

By which i mean that:

class Smeagol {
  private volatile int x;
  public int getX() {
  return x;
  }
  public void setX(int x) {
  this.x = x;
  }
}

And:

class Deagol {
  private int x;
  public synchronized int getX() {
  return x;
  }
  public synchronized void setX(int x) {
  this.x = x;
  }
}

Have slightly different semantics. If thread A calls getX, and then thread
B calls setX, then with Deagol, there is a happens-before relationship
between the two calls. With Smeagol, there is not. Whereas if A calls setX
and then B calls getX, both Smeagol and Deagol will generate a
happens-before relationship.

Or so i believe. I hope someone will correct me if i'm wrong.

The good news is that in most cases, the weaker guarantees provided by
Smeagol's volatile are actually just what you want (because you don't care
that a write to a variable happens after a read), and the JVM can generate
a more streamlined sequence of instructions for it.

tom

--
Eight-bit is forever