@Override
        public boolean canDestroy() {
            return currentEventChunk.getFirst() == null &&
                    (expiredEventChunk == null || expiredEventChunk.getFirst() == null) &&
                    resetEvent == null && flushed;
        }
Here an assumption is taken:
Parameter: timestamp: The time which the window determines as current time and will act upon,
the value of this parameter should be monotonically increasing.
from https://docs.wso2.com/display/CEP400/Inbuilt+Windows#InbuiltWindows-externalTime
modules/siddhi-core/src/main/java/io/siddhi/core/query/processor/stream/window/ExternalTimeBatchWindowProcessor.java