Method getAndAdd

output/java_guava/1.4.17/AtomicLongMap.java:169–199

Adds delta to the value currently associated with key, and returns the old value.

(K key, long delta)

   */

  @CanIgnoreReturnValue
  public long getAndAdd(K key, long delta) {
    outer:
    while (true) {
      AtomicLong atomic = map.get(key);
      if (atomic == null) {
        atomic = map.putIfAbsent(key, new AtomicLong(delta));
        if (atomic == null) {
          return 0L;
        }
        // atomic is now non-null; fall through
      }

      while (true) {
        long oldValue = atomic.get();
        if (oldValue == 0L) {
          // don't compareAndSet a zero
          if (map.replace(key, atomic, new AtomicLong(delta))) {
            return 0L;
          }
          // atomic replaced
          continue outer;
        }
        long newValue = oldValue + delta;
        if (atomic.compareAndSet(oldValue, newValue)) {
          return oldValue;
        }
        // value changed
      }
    }
  }

  /**
   * Associates {@code newValue} with {@code key} in this map, and returns the value previously