// since get returned null, try a putIfAbsent; that fails due to a simulated race
    when(backingMap.putIfAbsent(eq(KEY), isA(AtomicInteger.class))).thenReturn(existingZero);
    // since the putIfAbsent returned a zero, we'll try to replace...
    when(backingMap.replace(eq(KEY), eq(existingZero), isA(AtomicInteger.class))).thenReturn(false);
    // ...and then putIfAbsent. Simulate failure on both

    while (true) {
      AtomicInteger existingCounter = safeGet(countMap, element);
      if (existingCounter == null) {
        existingCounter = countMap.putIfAbsent(element, new AtomicInteger(occurrences));
        if (existingCounter == null) {
          return 0;
        }
        // existingCounter != null: fall through to operate against the existing AtomicInteger
      }

            if (!Modifier.isStatic(method.getModifiers()) && method.getParameterCount() == 1) {
                Type[] paramTypes = method.getGenericParameterTypes();
                methodMap.putIfAbsent(method.getName(), new MethodInfo(method, paramTypes[0]));
            }
        }

        return methodMap;
    }

    /**
     * Check if method is compatible with value type.
     */

        QueueHolder queueHolder = sessionCache.get(sessionId);
        if (queueHolder == null) {
            queueHolder = new QueueHolder();
            final QueueHolder prevQueueHolder = sessionCache.putIfAbsent(sessionId, queueHolder);
            return prevQueueHolder == null ? queueHolder : prevQueueHolder;
        }
        return queueHolder;
    }

    /**

    assertThrows(UnsupportedOperationException.class, () -> unmod.replaceAll((k, v) -> v));
    assertThrows(UnsupportedOperationException.class, () -> unmod.putIfAbsent(3, "three"));
    assertThrows(UnsupportedOperationException.class, () -> unmod.replace(3, "three", "four"));
    assertThrows(UnsupportedOperationException.class, () -> unmod.replace(3, "four"));
    assertThrows(

    @Override
    public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
      throw new UnsupportedOperationException();
    }

    @Override
    public @Nullable V putIfAbsent(K key, V value) {
      throw new UnsupportedOperationException();
    }

    @Override
    public boolean remove(@Nullable Object key, @Nullable Object value) {