@Override
  public void disallowOffHeapValues() {
    if (isOffHeapReference(newValue) || isOffHeapReference(oldValue)) {
      throw new IllegalStateException("This event already has off-heap values");
    }
    if (mayHaveOffHeapReferences()) {
      synchronized (offHeapLock) {
        offHeapOk = false;
      }
    } else {
      offHeapOk = false;
    }

  }
Make sure that this event will never own an off-heap value. Once this is called on an event it
does not need to have release called.
geode-core/src/main/java/org/apache/geode/internal/cache/EntryEventImpl.java