private static boolean isUnsupported(String key, SessionProtocol protocol) {
        final CacheEntry e;
        final long stamp = lock.readLock();
        try {
            e = cache.get(key);
        } finally {
            lock.unlockRead(stamp);
        }

        if (e == null) {
            // Can't tell if it's unsupported
            return false;
        }

        return e.isUnsupported(protocol);
    }
Returns {@code true} if the specified {@code remoteAddress} is known to have no support for
the specified {@link SessionProtocol}.
core/src/main/java/com/linecorp/armeria/client/SessionProtocolNegotiationCache.java