HashMap迭代器ConcurrentModificationException

我得到ConcurrentModificationException，我不知道如何解決它。HashMap迭代器ConcurrentModificationException

我有一個Android多線程應用程序（與套接字通信），我存儲回調（接口）到一個哈希映射。

public class ApiManager { 

    private static ApiManager instance; 

    public synchronized ApiManager getInstance() { 
     if (instance == null) 
     instance = new ApiManager(); 

     return instance; 
    } 

    private final HashMap<String, Callback> callbacks = new HashMap<>; 

    // Setters and getters for storing callbacks 

    private @Nullable Callback getCallback(@NoNull String key) { 
     synchronized (callbacks) { 
     return callbacks.get(key); 
     } 
    } 

    private void addCallback(@NonNull String key, @NonNull Callback callback) { 
     synchronized (callbacks) { 
     callbacks.put(key, callback); 
     } 
    } 

    private void removeCallback(@NonNull String key) { 
     synchronized (callbacks) { 
      callbacks.remove(key); 
     } 
    } 

    // Request to retrieve the user's profile from server 
    public synchronized void getProfile(String key, Callback callback) { 
     // Save the callback 
     addCallback(key, callback); 

     // Do the asynchronous request 
     getSocket().emit("getProfile", new Ack() { 
     @Override 
     public void call(Object... args) { 
      // Deliver the response 
      Callback callback = getCallback(key); 
      if (callback != null) 
       callback.onResponse(args); 

      // Remove the callback 
      removeCallback(key);     
     } 
     }); 
    } 

    // Called when the socket disconnects 
    // ----> This is the method where I get the exception ! 
    private void onSocketDisconnect() { 

     /* 
     * Notify stored callbacks that the socket has disconnected 
     */ 

     synchronized (callbacks) { 
     Set<Map.Entry<String, Callback>> set = callbacks.entrySet(); 
     if (set.size() > 0) { 
      Iterator<Map.Entry<String, Callback>> iterator = set.iterator(); 
      while (iterator.hasNext()) { 
       // This is the line where the exception occurres 
       Map.Entry<String, Callback> entry = iterator.next(); 

       String key = entry.getKey(); 
       Callback callback = entry.getValue(); 

       if (callback != null) { 
        // Notify callback that there was a socket disconnect exception 
       callback.onResponse(Factory.buildResponseFailure(SOCKET_DISC)); 

        it.remove(); 
       } 
      } 
     } 
     } 
    } 
}

有時異常occurres：

Exception: java.util.ConcurrentModificationException 
at java.util.HashMap$HashIterator.nextEntry(HashMap.java:851) 
     at java.util.HashMap$EntryIterator.next(HashMap.java:891) 
     at java.util.HashMap$EntryIterator.next(HashMap.java:890)

這是我如何獲取用戶的個人資料：

ApiManager.getInstance().getProfile(KEY_PROFILE_REQ, new Callback() { 
    @Override 
    public void onResponse(Object... args) { 
     // Parsing the data 
    } 
});

正如你可以看到我訪問的HashMap的塊。 ApiManager類是一個單例。如果我在迭代它的同時鎖定對象，爲什麼會得到ConcurrentModificationException？其他線程如何獲得鎖定？我錯過了什麼嗎？

注意：在這個例子中有3個線程。 UI線程（我稱之爲getProfile()方法），第二個線程是套接字的內部線程（傳遞響應），另一個線程調用onSocketDisconnected()方法。

來源

2017-05-30 Zbarcea Christian

訪問數據後，在while（iterator.hasNext（））塊中調用iterator.remove。 –

https://examples.javacodegeeks.com/java-basics/exceptions/java-util-concurrentmodificationexception-how-to-handle-concurrent-modification-exception/ – Stallion

在迭代同一個集合時從集合中刪除一個項目可能會導致此問題。您是否嘗試過將要刪除的項目存儲在某處，然後在處理完最後一個元素後，set.removeAll（某處）？

來源

2017-05-30 11:05:49 smutsig

HashMap迭代器ConcurrentModificationException

回答

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