@Override
              public void onCompletion(Void result, Exception exception) {
                metricsCollector.updateTimePassedSoFar(SystemTime.getInstance().milliseconds() - startTimeInMs);
                logger.trace("Deletion completed for {}", blobIdStr);
                countDownLatch.countDown();
                if (exception != null) {
                  logger.error("Deletion of {} failed with ", blobIdStr, exception);
                }
              }
Thread used for deleting blobs from ambry
ambry-tools/src/main/java/com/github/ambry/tools/admin/ConcurrencyTestTool.java