private static boolean isHealthy(PooledChannel pooledChannel) {
        final Channel ch = pooledChannel.get();
        return ch.isActive() && HttpSession.get(ch).isAcquirable();
    }
Attempts to acquire a {@link Channel} which is matched by the specified condition immediately.

@return {@code null} is there's no match left in the pool and thus a new connection has to be
        requested via {@link #acquireLater(SessionProtocol, SerializationFormat,
        PoolKey, ClientConnectionTimingsBuilder)}.
core/src/main/java/com/linecorp/armeria/client/HttpChannelPool.java