} catch (ExecutionException expected) {
                  }
                  try {
                    peeker.getDone(nonInput);
                    fail("Peeker should not be able to peek into non-input ClosingFuture.");
                  } catch (IllegalArgumentException expected) {
                  }
                  capturedPeeker.set(peeker);
                  return closeable2;
                },

    Deque<NodeAndRemainingSuccessors<N>> stack = new ArrayDeque<>();
    stack.addLast(new NodeAndRemainingSuccessors<>(startNode));

    while (!stack.isEmpty()) {
      // To peek at the top two items, we need to temporarily remove one.
      NodeAndRemainingSuccessors<N> top = stack.removeLast();
      NodeAndRemainingSuccessors<N> prev = stack.peekLast();
      stack.addLast(top);

      drainRecencyQueue();

      ReferenceEntry<K, V> e;
      while ((e = writeQueue.peek()) != null && map.isExpired(e, now)) {
        if (!removeEntry(e, e.getHash(), RemovalCause.EXPIRED)) {
          throw new AssertionError();
        }
      }
      while ((e = accessQueue.peek()) != null && map.isExpired(e, now)) {
        if (!removeEntry(e, e.getHash(), RemovalCause.EXPIRED)) {

    assertTrue(queue.add("hi"));
    assertThat(queue.element()).isEqualTo("hi");
    assertThat(queue.peek()).isEqualTo("hi");
    assertEquals(1, queue.size());
    assertEquals(0, queue.remainingCapacity());

    assertTrue(queue.add("there"));
    assertThat(queue.element()).isEqualTo("there");
    assertThat(queue.peek()).isEqualTo("there");
    assertEquals(1, queue.size());
    assertEquals(0, queue.remainingCapacity());

		buf := NewBufferString(test.buffer)
		buf.Next(test.skip)
		bytes, err := buf.Peek(test.n)
		if string(bytes) != test.expected {
			t.Errorf("expected %q, got %q", test.expected, bytes)
		}
		if err != test.err {
			t.Errorf("expected error %v, got %v", test.err, err)
		}
		if buf.Len() != len(test.buffer)-test.skip {
			t.Errorf("bad length after peek: %d, want %d", buf.Len(), len(test.buffer)-test.skip)
		}
	}
}

      drainRecencyQueue();

      ReferenceEntry<K, V> e;
      while ((e = writeQueue.peek()) != null && map.isExpired(e, now)) {
        if (!removeEntry(e, e.getHash(), RemovalCause.EXPIRED)) {
          throw new AssertionError();
        }
      }
      while ((e = accessQueue.peek()) != null && map.isExpired(e, now)) {
        if (!removeEntry(e, e.getHash(), RemovalCause.EXPIRED)) {

            context.pushedUserProperties = new HashSet<>();
            protoSession.getUserProperties().entrySet().stream()
                    .filter(k -> !sys.contains(k.getKey()))
                    .peek(k -> context.pushedUserProperties.add(k.getKey()))
                    .forEach(k -> System.setProperty(k.getKey(), k.getValue()));
        } else {
            protoSession.getUserProperties().entrySet().stream()

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

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

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

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

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

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

    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());
    assertThat(mmHeap.peek()).isNull();
    assertThat(mmHeap.peekLast()).isNull();