protected static void deleteFiles() {
    for (int i = 0; i < 4; i++) {
      File[] files = dirs[i].listFiles();
      if (files != null) {
        for (final File file : files) {
          file.delete();
        }
      }
    }
  }
cleans all the directory of all the files present in them
geode-core/src/integrationTest/java/org/apache/geode/internal/cache/diskPerf/MultiThreadedOplogPerJUnitPerformanceTest.java