@Override
    public void close() {
        if (!closed.getAndSet(true)) {
            synchronized (offsetReadFutures) {
                for (Future<Map<ByteBuffer, ByteBuffer>> offsetReadFuture : offsetReadFutures) {
                    try {
                        offsetReadFuture.cancel(true);
                    } catch (Throwable t) {
                        log.error("Failed to cancel offset read future", t);
                    }
                }
                offsetReadFutures.clear();
            }
        }
    }
Implementation of OffsetStorageReader. Unlike {@link OffsetStorageWriter} which is implemented
directly, the interface is only separate from this implementation because it needs to be
included in the public API package.
connect/runtime/src/main/java/org/apache/kafka/connect/storage/OffsetStorageReaderImpl.java