java - 迭代 HashMap 时出现 ConcurrentModificationException

Question

我在迭代 HashMap 时遇到 ConcurrentModificationException。

我该如何解决这个问题？

public void stopAllPlaying(int fadeDurationInMs)
{
    for(PlayThread thread : threadMap.values()) {
        if(thread != null) {
            thread.fadeOut(fadeDurationInMs);
        }
    }
    threadMap.clear();
}

更新:

不幸的是，使用lock似乎并没有解决这个问题。我已复制下面的错误消息

09-06 01:05:51.366: E/AndroidRuntime(1307): FATAL EXCEPTION: main
09-06 01:05:51.366: E/AndroidRuntime(1307): java.util.ConcurrentModificationException
09-06 01:05:51.366: E/AndroidRuntime(1307):     at java.util.HashMap$HashIterator.nextEntry(HashMap.java:796)
09-06 01:05:51.366: E/AndroidRuntime(1307):     at java.util.HashMap$ValueIterator.next(HashMap.java:828)
09-06 01:05:51.366: E/AndroidRuntime(1307):     at com.example.myapp.AudioTrackPlayer.stopAllPlaying(AudioTrackPlayer.java:141)
09-06 01:05:51.366: E/AndroidRuntime(1307):     at com.example.myapp.MyApp.stopAllSounds(MyApp.java:119)
09-06 01:05:51.366: E/AndroidRuntime(1307):     at com.example.myapp.MainActivity.stopPlayback(MainActivity.java:114)
09-06 01:05:51.366: E/AndroidRuntime(1307):     at com.example.myapp.MainActivity.onConfigurationChanged(MainActivity.java:451)
09-06 01:05:51.366: E/AndroidRuntime(1307):     at android.app.ActivityThread.performConfigurationChanged(ActivityThread.java:3397)
09-06 01:05:51.366: E/AndroidRuntime(1307):     at android.app.ActivityThread.handleConfigurationChanged(ActivityThread.java:3542)
09-06 01:05:51.366: E/AndroidRuntime(1307):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1121)
09-06 01:05:51.366: E/AndroidRuntime(1307):     at android.os.Handler.dispatchMessage(Handler.java:99)
09-06 01:05:51.366: E/AndroidRuntime(1307):     at android.os.Looper.loop(Looper.java:150)
09-06 01:05:51.366: E/AndroidRuntime(1307):     at android.app.ActivityThread.main(ActivityThread.java:4263)
09-06 01:05:51.366: E/AndroidRuntime(1307):     at java.lang.reflect.Method.invokeNative(Native Method)
09-06 01:05:51.366: E/AndroidRuntime(1307):     at java.lang.reflect.Method.invoke(Method.java:507)
09-06 01:05:51.366: E/AndroidRuntime(1307):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
09-06 01:05:51.366: E/AndroidRuntime(1307):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
09-06 01:05:51.366: E/AndroidRuntime(1307):     at dalvik.system.NativeStart.main(Native Method)

更新2:

我需要向修改 Hashmap 的所有实例添加锁!

Answer 1

private final Lock lock = new ReentrantLock();
public void stopAllPlaying(int fadeDurationInMs)
{
    lock.lock();
    try{
      for(PlayThread thread : threadMap.values()) {
          if(thread != null) {
              thread.fadeOut(fadeDurationInMs);
          }
      }
      threadMap.clear();
    }
    finally{
    lock.unlock();
    }
}

这应该可以完成工作。

您必须以相同的方式使用相同的 Lock 实例锁定 threadMap 的所有其他用法。

注意:这不是唯一进行同步的方法。

另请参阅http://developer.android.com/reference/java/util/concurrent/locks/Lock.html

您可能会发现这也很有帮助:http://docs.oracle.com/javase/tutorial/essential/concurrency/sync.html