@Override
  public void decTaskCounters(Collection<byte[]> regions, ServerName sn) {
    regions.forEach(regBytes -> {
      AtomicInteger regionCnt = taskCounterPerRegion.get(regBytes);
      regionCnt.decrementAndGet();
    });

    taskCounterPerServer.get(sn).decrementAndGet();
    tasksInProgress.decrementAndGet();
    synchronized (tasksInProgress) {
      tasksInProgress.notifyAll();
    }
  }
The number of task simultaneously executed on a single region server.
hbase-client/src/main/java/org/apache/hadoop/hbase/client/SimpleRequestController.java