code: public void forceClose() {
          // Move all elements from usedInstances to unusedInstances in a threadsafe way
          for (final T usedInstance : new ArrayList<>(usedInstances)) {
              if (usedInstances.remove(usedInstance)) {
                  unusedInstances.add(usedInstance);
              }
          }
          close();
      }
docs: Force-close this {@link Recycler}, by forcibly moving any instances that have been acquired but not yet
  recycled into the unused instances list, then calling {@link #close()} to close any {@link AutoCloseable}
  instances and discard all instances.