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ZooKeeper食谱和Apache Curator(ZooKeeper Recipes and Apache Curator)

 我试图了解Apache ZooKeeper（“ZK”）解决哪些类型的问题，也许他们的Recipes页面是最好的开始。  
 首先，我做了以下假设 ：  
 
  ZooKeeper API（可用Java和C提供）公开了这7种简单的方法 ，然后您可以建立自己的使用模式，即“ZK Recipes”  
  然后，您可以自己使用这些ZK Recipes来解决分布式编程中的问题  
  或者，您可以使用Apache Curator附带的那些，而不是构建自己的ZK食谱  
  因此无论哪种方式，您都在使用ZK Recipes（再次，本地生成或由Curator提供）来解决分布式计算问题  
 
 我相信Apache Kafka就是一个例子，Kafka使用ZK创建分布式队列 （这是列出的ZK食谱之一）。 所以如果我的假设是正确的，ZK公开这些API方法，并且Apache Kafka的创建者或者直接使用ZK或者使用Curator来实现“队列”ZK配方。  
 如果我上面的任何假设都是错误的，请首先纠正我！ 假设我或多或少地走上正轨：  
 看看ZK食谱的清单，我看到以下（非穷举）：  
 
  障碍  
  锁  
  领袖选举  
 
 为了让我欣赏这些食谱和他们提供的解决方案，我首先需要感谢他们解决的问题！ 我理解基本Java并发的锁是什么，但是我只是没有看到“分布式Lock”何时是必需的用例。 对于领先的选举，我所能想到的 - 作为一个首先需要它的用例 - 就是如果您正在构建一个应用程序，并希望通过内置的主/从或主/辅助功能发货。 也许在这种情况下，你会使用ZK来实现你自己的“领导者选举”配方，或者也许只是使用Curator的领导者锁定开箱即用。 至于障碍，我没有看到这些与Locks有什么不同。 所以我问：  
 
  我的主/奴隶问题或主要/次要问题是ZK领导人选举食谱的准确用例吗？  
  什么是分布式锁的例子？ 它解决了什么问题？  
  同上障碍：锁和障碍有什么区别？  

I am trying to understand exactly what types of problems Apache ZooKeeper ("ZK") solves, and perhaps their Recipes page is the best place to start. 
First off, I am making the following assumptions: 
 
 The ZooKeeper API (available in both Java and C) exposes these 7 simple methods which then allow you to build up your own usage patterns, known as "ZK Recipes" 
 It is then up to you to use these ZK Recipes to solve problems in distributed programming yourself 
 Or, instead of building up your own ZK Recipes, you could just use the ones that ship with Apache Curator 
 So either way, you're using ZK Recipes (again, homegrown or provided by Curator) to solve distributed computing problems 
 
I believe Apache Kafka is an example of this, where Kafka uses ZK to create a distributed Queue (which is one of the listed ZK Recipes). So if my assumptions are correct, ZK exposes those API methods, and the creators of Apache Kafka either used ZK directly or used Curator to implement the "Queue" ZK Recipe. 
If any of my above assumptions are wrong, please begin by correcting me! Assuming I'm more or less on track: 
Looking at the list of ZK Recipes, I see the following (non-exhaustive): 
 
 Barriers 
 Locks 
 Leader Election 
 
In order for me to appreciate these recipes and the solutions they present, I first need to appreciate the problem that they solve! I understand what a lock is from basic Java concurrency, but I'm just not seeing the use case for when a "distributed Lock" would ever be necessary. For leading election, all I can think of - as a use case for needing it in the first place - would be if you were building an application that you wanted to ship with a built-in master/slave or primary/secondary capability. Perhaps in that case you would use ZK to implement your own "Leader Election" recipe, or perhaps just use Curator's Leader Latch out of the box. As for Barriers, I don't see how those are any different than Locks. So I ask: 
 
 Is my master/slave or primary/secondary problem an accurate use case for ZK's Leader Election recipe? 
 What would be an example of a distributed Lock? What problem(s) does it solve? 
 Ditto for Barriers: and what's the difference between Locks and Barriers? 

原文：https://stackoverflow.com/questions/30871254

更新时间：2024-05-09 20:05

最满意答案

 代码中的以下行  
MainWindow *mw = new MainWindow(this);
 
 创建一个新的主窗口并更新它的列表。 我认为这确实发生了，但窗口从未显示过，所以你看不到它。 您真正想要做的是更新现有主窗口的列表。  
 基本上有两种方法。 你可以获得一个指向现有主窗口的指针（可以提供给对话框的构造函数或它自己的方法），也可以使用Qt的Signals and Slots概念，这是我认为的方法。  
 
  首先，在对话框的标题中定义信号： 
...
signals:
    void user_registered();
...
 
  然后你在函数中发出信号 
//MainWindow *mw = new MainWindow(this);
//mw->list();
emit this->user_registered();
 
  确保list()方法在MainWindow标头中声明为SLOT  
  连接MainWindow构造函数中的信号以调用list()槽： 
...
QObject::connect(this->dialog_test, SIGNAL(user_registered()), this, SLOT(list()));
...
 
 
 使用这种方法，对话框根本不需要知道主窗口。 它基本上只是告诉任何对用户注册感兴趣的人，并且主窗口自身完整地对其进行操作。 

The following line in your code 
MainWindow *mw = new MainWindow(this);
 
creates a new main window and updates the list of it. I assume this actually happens, but the window is never shown so you do not see any of it. What you actually want to do is update the list of your existing main window. 
There are basically two ways of doing that. You can either obtain a pointer to the existing main window (which can be provided to the constructor of the dialog or a method of its own) or use the Signals and Slots concept of Qt which is the way to go in my opinion. 
 
 First of all, you define the signal in the header of the dialog:
 ...
signals:
    void user_registered();
...
 
 Then you emit the signal in your function
 //MainWindow *mw = new MainWindow(this);
//mw->list();
emit this->user_registered();
 
 Make sure the list() method is declared as a SLOT in the MainWindow header 
 Connect the signal in the MainWindow constructor to call the list() slot:
 ...
QObject::connect(this->dialog_test, SIGNAL(user_registered()), this, SLOT(list()));
...
 
 
With this approach, the dialog does not need to know the main window at all. It basically just tells anyone who is interested that a user registered and the main window acts on it completly by itself.

ZooKeeper食谱和Apache Curator(ZooKeeper Recipes and Apache Curator)

最满意答案

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