在触发应用程序事件时创建bean时，如何避免Spring中的死锁？

Question

A deadlock occurs in my application while one thread performs a query on a mongo db, causing an application event to be fired, while another thread attempts to create a bean with an AutowireCapableBeanFactory .

This happens in the constructor of a @Service and prevents the startup of the entire application as the service is created on startup.

Pseudocode:

@Service
public class MyService {

    @Autowired
    public MyService(AutowireCapableBeanFactory factory, TaskScheduler scheduler) {
        MyFirstCommand command1 = factory.getBean(MyFirstCommand.class);
        scheduler.schedule(command1, new Date());

        MySecondCommand command2 = factory.getBean(MySecondCommand.class);
        scheduler.schedule(command2, new Date());
    }
}

public class MyFirstCommand extends Runnable {

    @Autowired MongoOperations mongo;

    @Override
    public void run() {
       mongo.findById("some-id", MyData.class); 
    }
}

Note that i have some AbstractMongoEventListener s registered as @Component s.

The deadlock occurs while one thread in MyFirstCommand.run() performs mongo.findById() . The other thread is in the constructor of MyService performing factory.getBean(MySecondCommand.class):

Found one Java-level deadlock:
=============================
"pool-1-thread-1":
  waiting to lock monitor 0x00007fd05d5bf5d8 (object 0x00000000816d0970, a java.util.concurrent.ConcurrentHashMap),
  which is held by "main"
"main":
  waiting for ownable synchronizer 0x0000000081ed8468, (a java.util.concurrent.locks.ReentrantReadWriteLock$NonfairSync),
  which is held by "pool-1-thread-1"


Java stack information for the threads listed above:
===================================================
"pool-1-thread-1":
at org.springframework.context.event.AbstractApplicationEventMulticaster.getApplicationListeners(AbstractApplicationEventMulticaster.java:179)
- waiting to lock <0x00000000816d0970> (a java.util.concurrent.ConcurrentHashMap)
at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:127)
at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:381)
at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:335)
at org.springframework.data.mapping.context.AbstractMappingContext.addPersistentEntity(AbstractMappingContext.java:326)
at org.springframework.data.mapping.context.AbstractMappingContext.getPersistentEntity(AbstractMappingContext.java:179)
at org.springframework.data.mapping.context.AbstractMappingContext.getPersistentEntity(AbstractMappingContext.java:139)
at org.springframework.data.mapping.context.AbstractMappingContext.getPersistentEntity(AbstractMappingContext.java:66)
at org.springframework.data.mongodb.core.MongoTemplate.determineCollectionName(MongoTemplate.java:1976)
at org.springframework.data.mongodb.core.MongoTemplate.findById(MongoTemplate.java:607)


"main":
at sun.misc.Unsafe.park(Native Method)
- parking to wait for  <0x0000000081ed8468> (a java.util.concurrent.locks.ReentrantReadWriteLock$NonfairSync)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireShared(AbstractQueuedSynchronizer.java:967)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireShared(AbstractQueuedSynchronizer.java:1283)
at java.util.concurrent.locks.ReentrantReadWriteLock$ReadLock.lock(ReentrantReadWriteLock.java:727)
at org.springframework.data.mapping.context.AbstractMappingContext.getPersistentEntity(AbstractMappingContext.java:160)
at org.springframework.data.mapping.context.AbstractMappingContext.getPersistentEntity(AbstractMappingContext.java:139)
at org.springframework.data.mapping.context.AbstractMappingContext.getPersistentEntity(AbstractMappingContext.java:66)
at org.springframework.data.mongodb.repository.support.MongoRepositoryFactory.getEntityInformation(MongoRepositoryFactory.java:118)
at org.springframework.data.mongodb.repository.support.MongoRepositoryFactory.getTargetRepository(MongoRepositoryFactory.java:92)
at org.springframework.data.repository.core.support.RepositoryFactorySupport.getRepository(RepositoryFactorySupport.java:185)
at org.springframework.data.repository.core.support.RepositoryFactoryBeanSupport.initAndReturn(RepositoryFactoryBeanSupport.java:251)
at org.springframework.data.repository.core.support.RepositoryFactoryBeanSupport.afterPropertiesSet(RepositoryFactoryBeanSupport.java:237)
at org.springframework.data.mongodb.repository.support.MongoRepositoryFactoryBean.afterPropertiesSet(MongoRepositoryFactoryBean.java:108)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1637)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1574)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:545)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482) 

How come Spring isn't thread safe here? What can i do to avoid this deadlock?

Answer 1

This deadlock occurs due to a bug in Spring. I have created an issue in their JIRA: DATACMNS-901 .

As a workaround i am now creating all runnable beans before scheduling them:

@Autowired
public MyService(AutowireCapableBeanFactory factory, TaskScheduler scheduler) {
    MyFirstCommand command1 = factory.getBean(MyFirstCommand.class);
    MySecondCommand command2 = factory.getBean(MySecondCommand.class);

    scheduler.schedule(command2, new Date());
    scheduler.schedule(command1, new Date());
}