@Override
    public void init(FileSystem fs, Path path, Configuration conf, boolean overwritable,
      long blocksize, StreamSlowMonitor monitor)
      throws IOException, CommonFSUtils.StreamLacksCapabilityException {
      Collection<String> operations = conf.getStringCollection(ALLOWED_OPERATIONS);
      if (operations.isEmpty() || operations.contains(AllowedOperations.all.name())) {
        doAppends = doSyncs = true;
      } else if (operations.contains(AllowedOperations.none.name())) {
        doAppends = doSyncs = false;
      } else {
        doAppends = operations.contains(AllowedOperations.append.name());
        doSyncs = operations.contains(AllowedOperations.sync.name());
      }
      LOG.info("IOTestWriter initialized with appends " + (doAppends ? "enabled" : "disabled")
        + " and syncs " + (doSyncs ? "enabled" : "disabled"));
      super.init(fs, path, conf, overwritable, blocksize, monitor);
    }
Presumes init will be called by a single thread prior to any access of other methods.
hbase-server/src/test/java/org/apache/hadoop/hbase/wal/IOTestProvider.java