user executorcompletionservice

HRegion.java

 CompletionService<HStore> completionService =
        new ExecutorCompletionService<HStore>(storeOpenerThreadPool);

      // initialize each store in parallel
      for (final HColumnDescriptor family : htableDescriptor.getFamilies()) {
        status.setStatus("Instantiating store for column family " + family);
        completionService.submit(new Callable<HStore>() {
          @Override
          public HStore call() throws IOException {
            return instantiateHStore(family);
          }
        });
      }