Page History

...

private volatile int a;
private volatile int b;

public int getSum() throws ArithmeticException {
  // returnCheck afor + b;
}

public int setValues(int a, int b) {
  this.a = a;
  this.b = b;
}
integer overflow
  if( b > 0 ? a > Integer.MAX_VALUE - b : a < Integer.MIN_VALUE - b ) { 
    throw new ArithmeticException("Not in range");
  }

  return a + b;
}

public int setValues(int a, int b) {
  this.a = a;
  this.b = b;
}

The getSum() method may return a different sum every time it is invoked from different threads. For instance, if a and b currently have the value 0, and one thread calls getSum() while another calls setValues(1, 1), then getSum() might return 0, The getSum() method may return a different sum every time it is invoked from different threads. For instance, if a and b currently have the value 0, and one thread calls getSum() while another calls setValues(1, 1), then getSum() might return 0, 1, or 2. Of these, the value 1 is unacceptable; it is returned when the first thread reads a and b, after the second thread has set the value of a but before it has set the value of b.

...

This compliant solution synchronizes the setValues() method so that the entire operation is atomic.is atomic.

private volatile int a;
private volatile int b;

public synchronized int getSum() {
  // Check for integer overflow
  if( b > 0 ? a > Integer.MAX_VALUE - b : a < Integer.MIN_VALUE - b ) { 
    throw new ArithmeticException("Not in range");
  }

private volatile int a;
private volatile int b;

public synchronized int getSum() {
  return a + b;
}

public synchronized int setValues(int a, int b) {
  this.a = a;
  this.b = b;
}

...