public Guard newGuard(BooleanSupplier isSatisfied) {
    checkNotNull(isSatisfied, "isSatisfied");
    return new Guard(this) {
      @Override
      public boolean isSatisfied() {
        return isSatisfied.getAsBoolean();
      }
    };
  }

  /** Enters this monitor. Blocks indefinitely. */
  public void enter() {
    lock.lock();
  }

  /**
   * Enters this monitor. Blocks at most the given time.