return delegate().offerFirst(e);
  }

  @CanIgnoreReturnValue // TODO(cpovirk): Consider removing this?
  @Override
  public boolean offerLast(@ParametricNullness E e) {
    return delegate().offerLast(e);
  }

  @Override
  @CheckForNull
  public E peekFirst() {
    return delegate().peekFirst();
  }

  @Override
  @CheckForNull
  public E peekLast() {

    return delegate().offerFirst(e, timeout, unit);
  }

  @Override
  public boolean offerLast(E e, long timeout, TimeUnit unit) throws InterruptedException {
    return delegate().offerLast(e, timeout, unit);
  }

  @Override
  public E takeFirst() throws InterruptedException {
    return delegate().takeFirst();
  }

  @Override

    public boolean offerFirst(E e) {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.offerFirst(e);
    }

    @Override
    public boolean offerLast(E e) {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.offerLast(e);
    }

    @Override
    public E removeFirst() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.removeFirst();
    }

    return delegate().offerFirst(e, timeout, unit);
  }

  @Override
  public boolean offerLast(E e, long timeout, TimeUnit unit) throws InterruptedException {
    return delegate().offerLast(e, timeout, unit);
  }

  @Override
  public E takeFirst() throws InterruptedException {
    return delegate().takeFirst();
  }

  @Override

    return delegate().offerFirst(e, timeout, unit);
  }

  @Override
  public boolean offerLast(E e, long timeout, TimeUnit unit) throws InterruptedException {
    return delegate().offerLast(e, timeout, unit);
  }

  @Override
  public E takeFirst() throws InterruptedException {
    return delegate().takeFirst();
  }

  @Override

    public boolean offerFirst(E e) {
      synchronized (mutex) {
        return delegate().offerFirst(e);
      }
    }

    @Override
    public boolean offerLast(E e) {
      synchronized (mutex) {
        return delegate().offerLast(e);
      }
    }

    @Override
    public E removeFirst() {
      synchronized (mutex) {
        return delegate().removeFirst();
      }
    }

    public boolean offerFirst(E e) {
      synchronized (mutex) {
        return delegate().offerFirst(e);
      }
    }

    @Override
    public boolean offerLast(E e) {
      synchronized (mutex) {
        return delegate().offerLast(e);
      }
    }

    @Override
    public E removeFirst() {
      synchronized (mutex) {
        return delegate().removeFirst();
      }
    }