PH45977: Duplicate execution of scheduleAtFixedRate

APAR status

• Closed as program error.

Error description

• scheduleAtFixedRate task that takes very little time to run can
  encounter a timing window where a duplicate execution occurs
  immediately after.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:  All users of IBM WebSphere Application      *
  *                  Server ManagedScheduledExecutorService      *
  ****************************************************************
  * PROBLEM DESCRIPTION: A ManagedScheduledExecutorService       *
  *                      scheduleAtFixedRate task that takes     *
  *                      very little time to run might           *
  *                      intermittently run again immediately    *
  *                      after.                                  *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  The task is somehow starting (and completing) before its
  scheduled time and so the computation of the next scheduled
  execution ends up being the same as the previously scheduled
  execution, causing the task to run a second time in the very
  near future, in violation of the fixed rate. Possibly there
  might have been a slight change to system time that causes
  this.
  

Problem conclusion

• The computation of fixed-rate was rewritten to first try
  adding on the fixed-rate amount to the previously scheduled
  execution time, which it uses if that time is in the future.
  Otherwise it falls back to computing a next time based on how
  many fixed-rate executions were missed.
  
  The fix for this APAR is targeted for inclusion in fix pack
  9.0.5.13. 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