ArrayList 上的 java.util.ConcurrentModificationException [英] java.util.ConcurrentModificationException on ArrayList

问题描述

我有一个 Server 类和一个里面的 Timer 应该清除死客户端(崩溃的客户端).我按照下面的示例在 Timer 迭代用户时锁定集合，但我仍然收到此异常(在连接的客户端崩溃后).

I have a Server class and a Timer inside it which is supposed to clear dead clients (clients who crashed). I followed the example below by locking the collection when the Timer iterates over the users but I still get this exception (after I crash a connected client).

http://www.javaperformancetuning.com/articles/fastfail2.shtml

List<User> users;
List<User> connectedUsers;
ConcurrentMap<User, IClient> clients;

...

users = Collections.synchronizedList(new ArrayList<User>());
connectedUsers = new ArrayList<User>();
clients = new ConcurrentHashMap<User, IClient>();
timer = new Timer();
timer.schedule(new ClearDeadClients(), 5000, 5000);

...

class ClearDeadClients extends TimerTask {
    public void run() {
        synchronized (users) {
            Iterator<User> it = users.iterator();
            while (it.hasNext()) {
                User user = it.next(); // Throws exception
                if (!connectedUsers.contains(user)) {
                    users.remove(user);
                    clients.remove(user);
                }
            }
        }       

        connectedUsers.clear();
    }
}

推荐答案

您需要从迭代器中删除而不是从集合中删除.它看起来像这样:

You need to remove from the iterator not the collection. It would look like this instead:

Iterator<User> it = users.iterator();
while (it.hasNext()) {
    User user = it.next(); 
    if (!connectedUsers.contains(user)) {
         it.remove();
         clients.remove(user);
     }
}

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