public static EventLoopGroup warmUp(EventLoopGroup eventLoopGroup) {
        requireNonNull(eventLoopGroup, "eventLoopGroup");

        eventLoopGroup.forEach(executor -> executor.submit(NO_OP));

        return eventLoopGroup;
    }
Warms up all {@link EventLoop}s in the given {@code eventLoopGroup}
by making sure all event loop threads are active.
core/src/main/java/com/linecorp/armeria/common/util/EventLoopGroups.java