code: public boolean isSharable() {
          /**
           * Cache the result of {@link Sharable} annotation detection to workaround a condition. We use a
           * {@link ThreadLocal} and {@link WeakHashMap} to eliminate the volatile write/reads. Using different
           * {@link WeakHashMap} instances per {@link Thread} is good enough for us and the number of
           * {@link Thread}s are quite limited anyway.
           *
           * See <a href="https://github.com/netty/netty/issues/2289">#2289</a>.
           */
          Class<?> clazz = getClass();
          Map<Class<?>, Boolean> cache = InternalThreadLocalMap.get().handlerSharableCache();
          Boolean sharable = cache.get(clazz);
          if (sharable == null) {
              sharable = clazz.isAnnotationPresent(Sharable.class);
              cache.put(clazz, sharable);
          }
          return sharable;
      }
docs: Return {@code true} if the implementation is {@link Sharable} and so can be added
  to different {@link ChannelPipeline}s.