PH36416: EJB SINGLETONBEAN POSSIBLE DEADLOCK DURING LIFECYCLE METHODS

APAR status

• Closed as program error.

Error description

• A Singleton Bean's @PostConstruct or @PreDestroy method can
  hit a deadlock.
  
  Scenario:
  The Singleton calls another managed object (like another
  session bean or asynchronous bean) OR the Singleton has a
  lifecycle interceptor. The other managed object calls the
  Singleton (either through an asynchronous method that is
  invoked at the right time ,so a timing problem, or through the
  method the Singleton called on it during it's lifecycle event)
  We deadlock because the Singleton is locked from the lifecycle
  event, but now the other managed object is waiting to acquire
  a lock on the Singleton at the same time as the Singleton
  lifecycle event is trying to obtain a lock on the other
  managed object.
  
  Workaround:
  Rewrite the other method of the interceptor or managed object
  to not aquire a write lock.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:  All users of IBM WebSphere Application      *
  *                  Server                                      *
  ****************************************************************
  * PROBLEM DESCRIPTION: Users can experience a deadlock while   *
  *                      an EJB Singleton bean is either         *
  *                      initializing or being destroyed.        *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  Users can experience a deadlock while
  an EJB Singleton bean is either
  initializing or being destroyed.
  This can cause a thread to either hang during server shutdown
  if the deadlock is during the destroy of the Singleton or
  cause a hung thread during application use if the deadlock is
  in the creation of the bean. A customer can experience both.
  

Problem conclusion

• For @PreDestroy we are no longer locking the Singleton bean,
  depending on when the destroy resolves, the other managed
  object might get an error stating the bean has been
  stopped/destroyed.
  
  For @PostConstruct the EJBContainer must lock the creation of
  SingletonBeans to ensure only one gets created. Instead of
  deadlocking forever we now have a timeout value of attempting
  to obtain a lock. This value is 2 minutes by default but
  configurable by @AccessTimeout value either on the class or
  the @PostConstruct method. A thread that times out trying to
  access the Singleton will get a
  javax.ejb.ConcurrentAccessTimeoutException
  
  The fix for this APAR is targeted for inclusion in fix pack
  9.0.5.10 and 8.5.5.21 for Websphere Application Server and
  21.0.0.7 for Liberty. For more information, see 'Recommended
  Updates for WebSphere Application Server':
  https://www.ibm.com/support/pages/node/715553
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

Fix information

• Fixed component name

  WEBS APP SERV N

• Fixed component ID

  5724H8800

Applicable component levels

• R850 PSY

     UP

• R900 PSY

     UP