"concurrency level was already set to %s",
        this.concurrencyLevel);
    checkArgument(concurrencyLevel > 0);
    this.concurrencyLevel = concurrencyLevel;
    return this;
  }

  int getConcurrencyLevel() {
    return (concurrencyLevel == UNSET_INT) ? DEFAULT_CONCURRENCY_LEVEL : concurrencyLevel;
  }

  /**
   * Specifies that each key (not value) stored in the map should be wrapped in a {@link