Netty Epoll的LT、ET模式使用场景，详见注释。

EpollChannelConfig.java

 /**
     * Set the {@link EpollMode} used. Default is
     * {@link EpollMode#EDGE_TRIGGERED}. If you want to use {@link #isAutoRead()} {@code false} or
     * {@link #getMaxMessagesPerRead()} and have an accurate behaviour you should use
     * {@link EpollMode#LEVEL_TRIGGERED}.
     *
     * <strong>Be aware this config setting can only be adjusted before the channel was registered.</strong>
     */
    public EpollChannelConfig setEpollMode(EpollMode mode) {
        if (mode == null) {
            throw new NullPointerException("mode");
        }
        try {
            switch (mode) {
            case EDGE_TRIGGERED:
                checkChannelNotRegistered();
                ((AbstractEpollChannel) channel).setFlag(Native.EPOLLET);
                break;
            case LEVEL_TRIGGERED:
                checkChannelNotRegistered();
                ((AbstractEpollChannel) channel).clearFlag(Native.EPOLLET);
                break;
            default:
                throw new Error();
            }
        } catch (IOException e) {
            throw new ChannelException(e);
        }
        return this;
    }

ServerCnx.java

    // pulsar ServerCnx
    public void startSendOperation() {
        if (++pendingSendRequest == MaxPendingSendRequests) {
            // When the quota of pending send requests is reached, stop reading from socket to cause backpressure on
            // client connection, possibly shared between multiple producers
            ctx.channel().config().setAutoRead(false);
        }
    }

    public void completedSendOperation(boolean isNonPersistentTopic) {
        if (--pendingSendRequest == ResumeReadsThreshold) {
            // Resume reading from socket
            ctx.channel().config().setAutoRead(true);
        }
        if (isNonPersistentTopic) {
            nonPersistentPendingMessages--;
        }
    }