线程池中的Guice DAO提供程序 - 查询变为'在转换中空闲' [英] Guice DAO Provider in thread pool - queries become 'idle in transation'

问题描述

我使用Java 8，Hibernate 5.1.0.Final和Guice 4.1.0。

  @Inject 
私人提供者< ExampleDAO> exampleDAOProvider; 
 
 public void test（）{
 
 ExecutorService threadPool = Executors.newFixedThreadPool（10）; 
 
 for（int i = 0; i <100; i ++）
 threadPool.execute（new Runnable（）{
 
 @Override 
 public void run（）{
 logger.info（exampleDAOProvider.find（1l））; 
 
} 
}）; 
 
 threadPool.shutdown（）; 
 
 $ b  

每个 test（）方法执行会在 pg_stat_activity 中产生10个（线程池大小）行。它们很简单 select * from 具有空闲事务状态并且永不消失的查询。所以我达到 hibernate.c3p0.max_size 限制，我的应用程序停止使用数据库。

数据库模块：

  public class ExampleModule extends PrivateModule {
 
 @Override 
 public void configure（）{
 
 install（new JpaPersistModule（example-persistence-unit）。properties（jpaProperties（）））; 
 
 bind（ExampleDAO.class）.to（ExampleDAOImpl.class）; 
 
公开（ExampleDAO.class）; 
 
 Key< PersistFilter> key = Key.get（PersistFilter.class，ExamplePersistenceUnit.class）; 
 bind（key）.to（PersistFilter.class）; 
揭露（关键）; 
 
 
  

我试过 @注入提供程序< ExampleDAO> exampleDAOProvider 放入任务类代码中，但它不会改变任何内容。如果我 @Inject exampleDAO ，那么我会遇到并发问题（ ConcurrentModificationException ），因为它使用相同的 EntityManager 。

如果我使用 @Inject Provider< ExampleDAO>没有多线程的exampleDAOProvider 或者直接 @Inject ExampleDAO exampleDAO ，它运行良好，连接被释放。

为什么会发生？如何获得多线程代码中发布的连接？

解决方案

我已经用 @注释了几乎所有的DAO方法Transactional ，这似乎解决了我的问题。处理完成后，交易将被提交并释放连接。没有标记为 @Transactional 方法，这些方法查询应在稍后保存在同一个 EntityManager 或<$ c中的实体$ c> Session 以避免使用 merge（）。请注意， @Transactional 仅适用于公共方法， synchronized 不适用于 @ Transactional 。

GenericDAOImpl使用 @Inject Provider< EntityManager> 代替



$ b $保护提供者< EntityManager> entityManagerProvider;

private EntityManager getEntityManager（）{
return entityManagerProvider.get（）;
}


相关讨论： Guice Persist是否提供事务范围或应用程序管理的EntityManager？

---

UDPATE 1

另一件事要检查：

• 如果您使用Hibernate 5.1.0.Final，那么persistence.xml应该包含：
  

< property name =hibernate.connection.provider_classvalue =org.hibernate.c3p0.internal.C3P0ConnectionProvider/>

而不是：

< property name =connection.provider_classvalue =org.hibernate.connection.C3P0ConnectionProvider/>

UDPATE 2

如果您使用

< property name =hibernate.enable_lazy_load_no_transvalue =tru e/>

延迟加载时可能导致连接泄漏。相关讨论：

• org.hibernate.LazyInitializationException - 无法初始化代理 - 没有会话 / li>
  

I use Java 8, Hibernate 5.1.0.Final and Guice 4.1.0.

@Inject
private Provider<ExampleDAO> exampleDAOProvider;

public void test(){

    ExecutorService threadPool = Executors.newFixedThreadPool(10);

    for (int i = 0; i < 100; i++)
        threadPool.execute(new Runnable() {

            @Override
            public void run() {
                logger.info(exampleDAOProvider.find(1l));

            }
        });

    threadPool.shutdown();

}

Every test() method execution will produce 10 (thread pool size) rows more in pg_stat_activity. They are simple select * from queries which have idle in transaction state and never disappear. So I reach hibernate.c3p0.max_size limit and my application stops working with database.

Database module:

public class ExampleModule extends PrivateModule {

    @Override
    public void configure() {

        install(new JpaPersistModule("example-persistence-unit").properties(jpaProperties()));

        bind(ExampleDAO.class).to(ExampleDAOImpl.class);

        expose(ExampleDAO.class);

        Key<PersistFilter> key = Key.get(PersistFilter.class, ExamplePersistenceUnit.class);
        bind(key).to(PersistFilter.class);
        expose(key);
    }
}

I have tried to @Inject Provider<ExampleDAO> exampleDAOProvider into the task class code but it does not change anything. If I @Inject exampleDAO, then I face concurrency issues (ConcurrentModificationException) because it uses the same EntityManager.

If I use @Inject Provider<ExampleDAO> exampleDAOProvider or direct @Inject ExampleDAO exampleDAO without multithreading, it works well and connections get released.

Why does it happen? How to get connections released in the multithreaded code?

解决方案

I have annotated almost every DAO method with @Transactional and this seems to solve my problem. After processing, transactions are committed and connections released. Didn't mark as @Transactional methods which query entities which should be persisted later in the same EntityManager or Session to avoid using merge(). Please note that @Transactional works only for public methods and synchronized doesn't work with @Transactional.

GenericDAOImpl use @Inject Provider<EntityManager> instead of @Inject EntityManager:

@Inject
protected Provider<EntityManager> entityManagerProvider;

private EntityManager getEntityManager() {
    return entityManagerProvider.get();
}

Related discussion: Does Guice Persist provide transaction scoped or application managed EntityManager?

---

UDPATE 1

Another things to check:

• If you're using Hibernate 5.1.0.Final, then persistence.xml should contain:

<property name="hibernate.connection.provider_class" value="org.hibernate.c3p0.internal.C3P0ConnectionProvider" />

Instead of:

<property name="connection.provider_class" value="org.hibernate.connection.C3P0ConnectionProvider" />

UDPATE 2

If you're using

<property name="hibernate.enable_lazy_load_no_trans" value="true" />

it may cause connection leaks when lazy loading. Related discussions:

• org.hibernate.LazyInitializationException - could not initialize proxy - no Session
• Solve Hibernate Lazy-Init issue with hibernate.enable_lazy_load_no_trans

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