EJB @Asynchronous检索实时插入行中JSF似乎是线程锁定 [英] EJB @Asynchronous to retrieve real time inserted row in JSF seems to be thread locked

问题描述

我想实现如下：

EJB3辛格尔顿

@Singleton
@Startup
public class SomeSingleton implements SomeSingletonLocal  {

    // Entity Manager injection
    private EntityManager _entity_manager;

    @Override
    @Asynchronous
    public void createScenario(){
        method1();
        method2();
        // ...
    }

    public void method1(){
        // Persist an Event in a Database.
    }

    public void method2(){
        // Persist an Event in a Database.
    }

}

托管Bean

@ManagedBean
@RequestScoped
public class SomeManagedBean{

    // Entity Manager injection
    private EntityManager _entity_manager;

    @EJB
    private SomeSingletonRemote _singleton;

    public void createScenario(){
        _singleton.createScenario();
    }

    public List<Event> getEventList(){
        // Retrieve events from database
    } 
}

JSF视图

<h:form>
    <p:commandButton value="Start Long Stuff" 
        actionListener="#{SomeManagedBean.createScenario}" />
    <h:outputText id="count" value="#{SomeManagedBean.getEventList.size()}" />
            <p:poll interval="1" update="count" />
</h:form>

登录

- > SomeManagedBean.getEventList（）结果
  ＆LT; -SomeManagedBean.getEventList（）//大小= 0

->SomeManagedBean.getEventList()
<-SomeManagedBean.getEventList() // Size = 0

//布顿点击搜索
   - > SomeManagedBean.createScenario（）结果
  ＆NBSP;＆NBSP;＆NBSP;＆NBSP;＆NBSP;＆NBSP; - > SomeSingleton.createScenario（）结果
  ＆LT; -SomeManagedBean.createScenario（）

// Buton clicked
->SomeManagedBean.createScenario()
      ->SomeSingleton.createScenario()
<-SomeManagedBean.createScenario()

- > SomeManagedBean.getEventList（）//将结束在SomeSingleton.createScenario结果的末尾
   - > SomeSingleton.method1（）结果
  ＆LT; -SomeSingleton.method1（）//坚持结果
   ...结果
   - > SomeSingleton.methodN（）结果
  ＆LT; -SomeSingleton.methodN（）//坚持

->SomeManagedBean.getEventList() // will end at the end of SomeSingleton.createScenario
->SomeSingleton.method1()
<-SomeSingleton.method1() // persist
...
->SomeSingleton.methodN()
<-SomeSingleton.methodN() // persist

＆LT; -SomeSingleton.createScenario（）

<-SomeSingleton.createScenario()

＆LT; -SomeManagedBean.getEventList（）//大小= N

<-SomeManagedBean.getEventList() // size = N

我预计至少有一个呼叫两个methodI（）调用之间getEventList（即每秒）。当它在SomeSingleton.createScenario（进入），我不知道为什么getEventList暂停。

I expected at least one call to getEventList between two methodI() call (ie. each second). When it enters in SomeSingleton.createScenario(), I dont know why getEventList is paused.

它看起来像有与实体管理器或内部createScenario事务的锁。那是一个重入的问题？

It looks like there is a lock with the entity manager or the transaction inside createScenario. Is that a reentrance problem ?

推荐答案

A @Singleton 确实是默认的读/写锁定。这不是严格相关的交易，但并发性。另请参见A.O。 的Java EE 7教程的主题。

A @Singleton is indeed by default read/write locked. This is not strictly related to transactions, but to concurrency. See also a.o. Java EE 7 tutorial on the subject.

要解决它的方法之一是设置<一个href=\"https://docs.oracle.com/javaee/7/api/javax/ejb/ConcurrencyManagement.html\"><$c$c>@ConcurrencyManagement到<一个href=\"https://docs.oracle.com/javaee/7/api/javax/ejb/ConcurrencyManagementType.html#BEAN\"><$c$c>BEAN.这样，你基本上告诉容器都不用担心并发和你承担自己的全部责任。

One way to solve it is to set the @ConcurrencyManagement to BEAN. This way you basically tell the container to not worry about concurrency at all and that you take all responsibility on your own.

@Singleton
@ConcurrencyManagement(ConcurrencyManagementType.BEAN)
public class SomeSingleton {}

另一种方法是明确设置 @Lock 以 读 。只有当一个方法的显式 @Lock（LockType.WRITE）上调用同一个实例，那么就会出现锁。

Another way is to explicitly set @Lock to READ on the class or the read-only methods so that they can concurrently be invoked. Only when a method with an explicit @Lock(LockType.WRITE) is invoked on the same instance, then the lock will occur.

@Singleton
@Lock(LockType.READ)
public class SomeSingleton {}

这篇关于EJB @Asynchronous检索实时插入行中JSF似乎是线程锁定的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！