防止spymemcached

Question

我试图用spymemcached 2.6与更新同步冲突，我发现以下两种方式来使用它：使用CASMutation定义CASMutator这是相当实施侵入性的方式

• 它，让看到一个例子：使用cas方法

  ​​

或通过

cas(String key, long casId, Object value) 

后都做：

gets(String key, Transcoder<T> tc) 

第二个是真的比较简单，我明白为什么我会用CASMutation ... 我会很高兴，以获取有关使用该couchbase的一些反馈客户。

Answer 1

CASMutator/CASMutation捕捉最佳实践和工作流程，以便为您完成正确的事情。

你的反例看起来更简单，因为你不说的话，你会真正做与方法。您上面发布的示例显示了一个正在从Memcached中取出的List，添加了一个新项目，有条件地从中删除一些项目，然后将其重新放回。您发布的文本中至少有一半仍需要编写。

如果您不是请使用 CASMutator，您最终将重新发明它，这并非如此简单。这就是它为你今天做的：

public T cas(final String key, final T initial, int initialExp, 
     final CASMutation<T> m) throws Exception { 
    T rv=initial; 

    boolean done=false; 
    for(int i=0; !done && i<max; i++) { 
     CASValue<T> casval=client.gets(key, transcoder); 
     T current=null; 
     // If there were a CAS value, check to see if it's compatible. 
     if(casval != null) { 
      T tmp = casval.getValue(); 
      current=tmp; 
     } 
     // If we have anything mutate and CAS, else add. 
     if(current != null) { 
      // Declaring this impossible since the only way current can 
      // be non-null is if casval was set. 
      assert casval != null : "casval was null with a current value"; 

      rv=m.getNewValue(current); 
      // There are three possibilities here: 
      // 1) It worked and we're done. 
      // 2) It collided and we need to reload and try again. 
      // 3) It disappeared between our fetch and our cas. 
      // We're ignoring #3 because it's *extremely* unlikely and the 
      // behavior will be fine in this code -- we'll do another gets 
      // and follow it up with either an add or another cas depending 
      // on whether it exists the next time. 
      if(client.cas(key, casval.getCas(), rv, transcoder) 
        == CASResponse.OK) { 
       done=true; 
      } 
     } else { 
      // No value found, try an add. 
      if(initial == null) { 
       done = true; 
       rv = null; 
      } else if(client.add(key, initialExp, initial, transcoder).get()) { 
       done=true; 
       rv=initial; 
      } 
     } 
    } 
    if(!done) { 
     throw new RuntimeException("Couldn't get a CAS in " + max 
      + " attempts"); 
    } 

    return rv; 
}