private void flushFlusher(boolean async) throws InterruptedException {
    if (!isFlusherTerminated()) {
      FlushNotifier fn = new FlushNotifier();
      addAsyncItem(fn, true);
      if (isFlusherTerminated()) {
        rmAsyncItem(fn);
      } else {
        incForceFlush();
        if (!async) {
          fn.waitForFlush();
        }
      }
    }
  }
force a flush but do it async (don't wait for the flush to complete).
geode-core/src/main/java/org/apache/geode/internal/cache/DiskStoreImpl.java