Java concurrentHashMap迭代
我使用的是一个线程,我们称之为MapChecker,它在ConcurrentHashMap的整个生命周期中都在循环 该映射由其他线程填充,并由MapChecker使用迭代器清除 该地图具有以下结构:Java concurrentHashMap迭代,java,concurrency,synchronized,concurrenthashmap,Java,Concurrency,Synchronized,Concurrenthashmap,我使用的是一个线程,我们称之为MapChecker,它在ConcurrentHashMap的整个生命周期中都在循环 该映射由其他线程填充,并由MapChecker使用迭代器清除 该地图具有以下结构: private volatile Map<MyObject, SynchronizedList<MyOtherObject>> map = new ConcurrentHashMap<>(); //SynchronizedList = Collections.sy
private volatile Map<MyObject, SynchronizedList<MyOtherObject>> map = new ConcurrentHashMap<>();
//SynchronizedList = Collections.syncrhonizedList.
MapChecker必须更新循环中每个键的值。通过从列表中删除元素或删除完整地图条目来进行更新
同步分两步进行:
在地图内添加数据时同步
检索MapChecker内同步的贴图的迭代器时。
这些锁位于mapitself synchronizedmap上
我不想总是在迭代器视图中保存最后更新的值,但我需要确保在下一次迭代中检索所有缺少的值,这一点很重要,因为我不想跳过任何元素。此外,正确更新SynchronizedList也很重要
我的问题是:
我是否可以通过使用这种体系结构确保插入/更新所有条目?有错过什么的风险吗?
如果MapChecker删除一个条目,而另一个线程正在更新该条目,会发生什么情况?ConcurrentHashMap应该会阻止这些操作,所以我希望不会有任何问题
这是MapChecker循环:
while (!isInterrupted()) {
executeClearingPhases();
Iterator<Map.Entry<PoolManager, List<PooledObject>>> it = null;
synchronized (idleInstancesMap) {
it = idleInstancesMap.entrySet().iterator();
}
while (it.hasNext()) {
Map.Entry<PoolManager, List<PooledObject>> entry = it.next();
PoolManager poolManager = entry.getKey();
boolean stop = false;
while (!stop) {
//this list is empty very often but it shouldn't, that's the problem I am facing. I need to assure updates visibility.
List<PooledObject> idlePooledObjects = entry.getValue();
if (idlePooledObjects.isEmpty()) {
stop = true;
} else {
PooledObject pooledObject = null;
try {
pooledObject = idlePooledObjects.get(0);
info(loggingId, " - REMOOOVINNGG: \"", pooledObject.getClientId(), "\".");
PoolingStatus destroyStatus = poolManager.destroyIfExpired(pooledObject);
switch (destroyStatus) {
case DESTROY:
info(loggingId, " - Removed pooled object \"", pooledObject.getClientId(), "\" from pool: \"", poolManager.getClientId(), "\".");
idlePooledObjects.remove(0);
break;
case IDLE:
stop = true;
break;
default:
idlePooledObjects.remove(0);
break;
}
} catch (@SuppressWarnings("unused") PoolDestroyedException e) {
warn(loggingId, " - WARNING: Pooled object \"", pooledObject.getClientId(), "\" skipped, pool: \"", poolManager.getClientId(), "\" has been destroyed.");
synchronized(idleInstancesMap) {
it.remove();
}
stop = true;
} catch (PoolManagementException e) {
error(e, loggingId, " - ERROR: Errors occurred during the operation.");
idlePooledObjects.remove(0);
}
}
}
}
Thread.yield();
}
这是任何其他线程多次调用的方法:
public void addPooledObject(PoolManager poolManager, PooledObject pooledObject) {
synchronized (idleInstancesMap) {
List<PooledObject> idleInstances = idleInstancesMap.get(poolManager);
if (idleInstances == null) {
idleInstances = Collections.synchronizedList(new LinkedList<PooledObject>());
idleInstancesMap.put(poolManager, idleInstances);
}
idleInstances.add(pooledObject);
}
}
谢谢
但我需要确保在下一次迭代中检索到所有缺少的值,这一点很重要,因为我不想跳过任何元素
首先,我认为基于您的解决方案,只要您继续执行MapChecker循环,我认为您将获得地图中的所有项目。我建议您在当前的MapChecker代码之外有一个额外的whiletrue循环
但是根据您的描述,我建议您应该使用队列而不是映射,显然,您的问题需要一个push/pop操作,也许BlockingQueue更适合这里。多亏PatrickChen的建议,我将PooledObject实例列表移到了每个已经拥有该列表的PoolManager中,因为它以完全同步的方式拥有该池及其内部状态 结果是:
//MapChecker lifecycle
public void run() {
try {
while (!isInterrupted()) {
executeClearingPhases();
ListIterator<PoolManager> it = null;
//This really helps. poolManagers is the list of PoolManager instances.
//It's unlikely that this list will have many elements (maybe not more than 20)
synchronized (poolManagers) {
Iterator<PoolManager> originalIt = poolManagers.iterator();
while (originalIt.hasNext()) {
if (originalIt.next().isDestroyed()) {
originalIt.remove();
}
}
//This iterator will contain the current view of the list.
//It will update on the next iteration.
it = new LinkedList<PoolManager>(poolManagers).listIterator();
}
while (it.hasNext()) {
PoolManager poolManager = it.next();
try {
//This method will lock on its internal synchronized pool in order to
//scan for expired objects.
poolManager.destroyExpired();
} catch (@SuppressWarnings("unused") PoolDestroyedException e) {
warn(loggingId, " - WARNING: Pool: \"", poolManager.getClientId(), "\" has been destroyed.");
it.remove();
}
}
Thread.yield();
}
throw new InterruptedException();
} catch (@SuppressWarnings("unused") InterruptedException e) {
started = false;
Thread.currentThread().interrupt();
debug(loggingId, " - Pool checker interrupted.");
}
}
//Method invoked by multiple threads
public void addPooledObject(PoolManager poolManager) {
synchronized (poolManagers) {
poolManagers.add(poolManager);
}
}
为什么地图本身是不稳定的?你不能让它成为最终的吗?你如何在地图上得到一个迭代器?在检索映射的迭代器时,映射未定义迭代器方法,ConcurrentHashMap.synchronized也未定义迭代器方法。你是说整个迭代都在关键部分?或者只是检索迭代器本身?您好@daniu,我正在映射的入口集上使用迭代器。问题是,您将变量映射声明为volatile表明您可能不理解此修饰符的作用。变量映射不应该改变,最好通过声明变量final来证明它没有改变。是的,但问题是我需要为每个PoolManager对象创建一个插入顺序列表。因此,使用队列不是一个选项,因为我可能必须在每个列表中添加新条目或新元素。所有PoolManager都会生成PooledObject,对吗?为什么不将PoolManager信息添加到PoolObject中,这样您就可以只保留一个队列,不需要映射。解决了!根据你的建议,我改变了我的数据结构,现在代码更干净、更有效。谢谢