code: @Override
      public void close() {
          if (!this.closed.getAndSet(true)) {
              // Close all open containers and notify their handles - as this was an unrequested stop.
              ArrayList<ContainerWithHandle> toClose = new ArrayList<>(this.containers.values());
              for (ContainerWithHandle c : toClose) {
                  c.container.close();
              }
          }
      }
docs: region AutoCloseable Implementation