java - 可运行中的 ConcurrentModificationException

Question

我正在开发一个计时器管理器，它将允许多个倒计时器，但我似乎无法弄清楚如何避免此 ConcurrentModificationException。我看过其他人对类似问题的 react ，但仍然无法弄清楚。

mHandler = new Handler();

        mUpdateUI = new Runnable() {
            public void run() {

        Iterator<HashMap.Entry<String, TimerHolder>> it = mTimers.entrySet().iterator();
            while (it.hasNext()) {
   -----------> Map.Entry<String, TimerHolder> pairs = it.next();
                pairs.getValue().post();
            }

            Iterator<HashMap.Entry<String, TimerHolder>> iterator = mTimers.entrySet().iterator();
            while (iterator.hasNext()) {
                HashMap.Entry<String, TimerHolder> entry = iterator.next();
                if (!entry.getValue().isValid()) {
                   iterator.remove();
                }
            }                   


                mHandler.postDelayed(mUpdateUI, 1000); // 1 second
            }
        };
        mHandler.post(mUpdateUI);

<小时/>

06-02 12:37:23.746: E/AndroidRuntime(10669): FATAL EXCEPTION: main
06-02 12:37:23.746: E/AndroidRuntime(10669): java.util.ConcurrentModificationException
06-02 12:37:23.746: E/AndroidRuntime(10669):    at java.util.HashMap$HashIterator.nextEntry(HashMap.java:806)
06-02 12:37:23.746: E/AndroidRuntime(10669):    at java.util.HashMap$EntryIterator.next(HashMap.java:843)
06-02 12:37:23.746: E/AndroidRuntime(10669):    at java.util.HashMap$EntryIterator.next(HashMap.java:841)
06-02 12:37:23.746: E/AndroidRuntime(10669):    at com.watcher.timer.TimerManager$1.run(TimerManager.java:57)
06-02 12:37:23.746: E/AndroidRuntime(10669):    at android.os.Handler.handleCallback(Handler.java:730)
06-02 12:37:23.746: E/AndroidRuntime(10669):    at android.os.Handler.dispatchMessage(Handler.java:92)
06-02 12:37:23.746: E/AndroidRuntime(10669):    at android.os.Looper.loop(Looper.java:137)
06-02 12:37:23.746: E/AndroidRuntime(10669):    at android.app.ActivityThread.main(ActivityThread.java:5493)
06-02 12:37:23.746: E/AndroidRuntime(10669):    at java.lang.reflect.Method.invokeNative(Native Method)
06-02 12:37:23.746: E/AndroidRuntime(10669):    at java.lang.reflect.Method.invoke(Method.java:525)
06-02 12:37:23.746: E/AndroidRuntime(10669):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1209)
06-02 12:37:23.746: E/AndroidRuntime(10669):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1025)
06-02 12:37:23.746: E/AndroidRuntime(10669):    at dalvik.system.NativeStart.main(Native Method)

Answer 1

实际上您的问题与并发无关。您的 Runnable 始终从同一个线程 - Main 线程调用，因为您将其发布到 Handler。

ConcurrentModificationException 被抛出，因为您尝试在 for-each 循环内修改集合。这是快速失败行为，目的是保护非线程安全集合免受潜在的并发修改的影响。您需要显式使用 Iterator 并在迭代器对象上调用 remove 。您的“删除无效条目”部分应如下所示:

Iterator<HashMap.Entry<String, TimerHolder>> iterator = mTimers.entrySet().iterator();
while (iterator.hasNext()) {
    HashMap.Entry<String, TimerHolder> entry = iterator.next();
    if (!entry.getValue().isValid()) {
       iterator.remove();
    }
}