下面是getGroupChannelTable（）的实现，我想知道为什么不只是返回groupChannelTable：

https://github.com/apache/rocketmq/blob/master/broker/src/main/java/org/apache/rocketmq/broker/client/ProducerManager.java

private final HashMap<String /* group name */, HashMap<Channel, ClientChannelInfo>> groupChannelTable =
    new HashMap<String, HashMap<Channel, ClientChannelInfo>>();

public HashMap<String, HashMap<Channel, ClientChannelInfo>> getGroupChannelTable() {
    HashMap<String /* group name */, HashMap<Channel, ClientChannelInfo>> newGroupChannelTable =
        new HashMap<String, HashMap<Channel, ClientChannelInfo>>();
    try {
        if (this.groupChannelLock.tryLock(LOCK_TIMEOUT_MILLIS, TimeUnit.MILLISECONDS)) {
            try {
                newGroupChannelTable.putAll(groupChannelTable);
            } finally {
                groupChannelLock.unlock();
            }
        }
    } catch (InterruptedException e) {
        log.error("", e);
    }
    return newGroupChannelTable;
}
java rocketmq