return delegate().offerLast(e);
  }

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

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

  @CanIgnoreReturnValue // TODO(cpovirk): Consider removing this?
  @Override
  @CheckForNull
  public E pollFirst() {
    return delegate().pollFirst();
  }

    public @Nullable E peekFirst() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.peekFirst();
    }

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

    @Override
    public boolean removeFirstOccurrence(Object o) {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.removeFirstOccurrence(o);

    assertEquals(4, (int) mmHeap.pollLast());
    assertEquals(3, (int) mmHeap.peekLast());
    assertEquals(3, (int) mmHeap.pollLast());
    assertEquals(1, (int) mmHeap.peek());
    assertEquals(2, (int) mmHeap.peekLast());
    assertEquals(2, (int) mmHeap.pollLast());
    assertEquals(1, (int) mmHeap.peek());
    assertEquals(1, (int) mmHeap.peekLast());
    assertEquals(1, (int) mmHeap.pollLast());
    assertNull(mmHeap.peek());

 * defined as the <i>least</i> element in the queue according to the queue's comparator. But unlike
 * a regular priority queue, the methods {@link #peekLast}, {@link #pollLast} and {@link
 * #removeLast} are also provided, to act on the <i>greatest</i> element in the queue instead.
 *
 * <p>A min-max priority queue can be configured with a maximum size. If so, each time the size of

    public @Nullable E peekFirst() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.peekFirst();
    }

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

    @Override
    public boolean removeFirstOccurrence(Object o) {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.removeFirstOccurrence(o);

    assertEquals(4, (int) mmHeap.pollLast());
    assertEquals(3, (int) mmHeap.peekLast());
    assertEquals(3, (int) mmHeap.pollLast());
    assertEquals(1, (int) mmHeap.peek());
    assertEquals(2, (int) mmHeap.peekLast());
    assertEquals(2, (int) mmHeap.pollLast());
    assertEquals(1, (int) mmHeap.peek());
    assertEquals(1, (int) mmHeap.peekLast());
    assertEquals(1, (int) mmHeap.pollLast());
    assertNull(mmHeap.peek());

    return delegate().offerLast(e);
  }

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

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

  @CanIgnoreReturnValue // TODO(cpovirk): Consider removing this?
  @Override
  @CheckForNull
  public E pollFirst() {
    return delegate().pollFirst();
  }

    public E peekFirst() {
      synchronized (mutex) {
        return delegate().peekFirst();
      }
    }

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

    @Override
    public boolean removeFirstOccurrence(@CheckForNull Object o) {
      synchronized (mutex) {