Question

我正在查询GAE数据存储区以检索实体列表（使用带有sdk 1.8.3的dev gae）：

public List<OT> getAll() {
    PersistenceManager pm = PMF.get().getPersistenceManager();
    Query q = pm.newQuery();
    q.setClass(OT.class);
    try {
        return (List<OT>) q.execute();
    }
    finally {
        q.closeAll();
        pm.close();
    }
}

这总是在ConcurrentModificationException行投放pm.close()：

java.util.ConcurrentModificationException
    at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:819)
    at java.util.ArrayList$Itr.next(ArrayList.java:791)
    at com.google.appengine.datanucleus.DatastoreConnectionFactoryImpl$DatastoreManagedConnection.close(DatastoreConnectionFactoryImpl.java:146)
    at org.datanucleus.store.connection.ConnectionManagerImpl.closeAllConnections(ConnectionManagerImpl.java:181)
    at org.datanucleus.store.AbstractStoreManager$1.preClose(AbstractStoreManager.java:260)
    at org.datanucleus.ObjectManagerImpl.close(ObjectManagerImpl.java:1112)
    at org.datanucleus.api.jdo.JDOPersistenceManager.internalClose(JDOPersistenceManager.java:359)
    at org.datanucleus.api.jdo.JDOPersistenceManagerFactory.releasePersistenceManager(JDOPersistenceManagerFactory.java:1106)
    at org.datanucleus.api.jdo.JDOPersistenceManager.close(JDOPersistenceManager.java:343)

我使用以下依赖项：

    <dependency>
        <groupId>com.google.appengine.orm</groupId>
        <artifactId>datanucleus-appengine</artifactId>
        <version>2.0.1.1</version>
    </dependency>
    <dependency>
        <groupId>org.datanucleus</groupId>
        <artifactId>datanucleus-core</artifactId>
        <version>3.1.3</version>
    </dependency>
    <dependency>
        <groupId>org.datanucleus</groupId>
        <artifactId>datanucleus-api-jdo</artifactId>
        <version>3.1.3</version>
    </dependency>
    <dependency>
        <groupId>javax.jdo</groupId>
        <artifactId>jdo-api</artifactId>
        <version>[3.0, 4.0)</version>
    </dependency>
    <dependency>
        <groupId>org.datanucleus</groupId>
        <artifactId>datanucleus-rdbms</artifactId>
        <version>3.1.3</version>
        <scope>runtime</scope>
    </dependency>

以及DN增强器的以下版本：

    <dependency>
        <groupId>org.datanucleus</groupId>
        <artifactId>datanucleus-enhancer</artifactId>
        <version>3.1.1</version>
    </dependency>

我没有对集合中的任何对象或集合本身进行任何修改。事实上，即使收集是空的，也会发生错误...... 知道我可能做错了什么吗？

其他调试详情 我已经在pm.close（）语句中进入了调试模式，发现在迭代侦听器时，其中一个是从侦听器列表中删除自己：

447468239@qtp-1694835335-71@11277, prio=5, in group 'main', status: 'RUNNING'
  at org.datanucleus.store.connection.ConnectionManagerImpl$1.managedConnectionPostClose(ConnectionManagerImpl.java:247)
  at com.google.appengine.datanucleus.DatastoreConnectionFactoryImpl$DatastoreManagedConnection.close(DatastoreConnectionFactoryImpl.java:147)
  at org.datanucleus.store.connection.ConnectionManagerImpl.closeAllConnections(ConnectionManagerImpl.java:181)
  at org.datanucleus.store.AbstractStoreManager$1.preClose(AbstractStoreManager.java:260)
  at org.datanucleus.ObjectManagerImpl.close(ObjectManagerImpl.java:1112)
  at org.datanucleus.api.jdo.JDOPersistenceManager.internalClose(JDOPersistenceManager.java:359)
  at org.datanucleus.api.jdo.JDOPersistenceManagerFactory.releasePersistenceManager(JDOPersistenceManagerFactory.java:1106)
  at org.datanucleus.api.jdo.JDOPersistenceManager.close(JDOPersistenceManager.java:343)
  at net.mycrub.jacasse.persistence.dao.GenericDAO.getAll(GenericDAO.java:43)

ConnectionManagerImpl.java上的代码：247

                    // Remove this listener
                    mconn.removeListener(this);

这不是我自己添加的听众。它实际上是在Query.closeAll()语句中添加的DN侦听器。我应该保留这两个中的任何一个＆＃34;关闭＆＃34;陈述，它们是多余的吗？

Answer 1

你尝试过这样的事吗？

public List<OT> getAll()
{
  List<OT> liResult = null;

  PersistenceManager pm = PMF.get().getPersistenceManager();
  Query q = pm.newQuery();
  try
  {
    q.setClass(OT.class);
    liResult = (List<OT>)q.execute();
  }
  finally
  {
    try
    {
      q.closeAll();
    }
    finally
    {
      pm.close();
    }
  }

  return liResult;
}

Answer 2

DatastoreManagedConnection#close()方法只是

public void close() {
    for (ManagedConnectionResourceListener listener : listeners) {
        listener.managedConnectionPreClose();
    }
    // nothing to actually close
    for (ManagedConnectionResourceListener listener : listeners) {
        listener.managedConnectionPostClose();
    }
}

ConcurrentModificationException无法直接来自此处，因为此代码中的任何内容都不会修改listeners List。是否可以并行运行其他代码并在listeners中添加或删除，调用addListener或removeListener？

使用JDO从GAE数据存储区读取时出现ConcurrentModificationException

2 个答案: