android/guava/src/com/google/common/util/concurrent/AtomicLongMap.java
public long sum() {
    long sum = 0L;
    for (AtomicLong value : map.values()) {
      sum = sum + value.get();
    }
    return sum;
  }
public long sum() {
    long sum = 0L;
    for (AtomicLong value : map.values()) {
      sum = sum + value.get();
    }
    return sum;
  }
Returns the sum of all values in this map.

<p>This method is not atomic: the sum may or may not include other concurrent operations.