private void waitAsyncFlushingDone() throws InterruptedException {
        // wait for previous flushings
        offer(new SinkBufferEntity(null, null, null));
        offer(new SinkBufferEntity(null, null, null));
        checkFlushException();
    }
async flush

@return false if met eof and flush thread will exit.
inlong-sort/sort-flink/sort-flink-v1.13/sort-connectors/starrocks/src/main/java/org/apache/inlong/sort/starrocks/manager/StarRocksSinkManager.java