IT40382: High CPU usage for IBM MQ amqzlaa0 process

APAR status

• Closed as program error.

Error description

• Operating system resource monitoring tools show that
  one or more amqzlaa0 processes have a continuously
  high CPU usage.
  
  A diagnostic trace of the affected process shows that a thread
  is constantly looping with the following error:
  
  --}! zcpReceiveOnPipe rc=zrcC_E_SHUTDOWN
  

Local fix

Problem summary

• ****************************************************************
  USERS AFFECTED:
  There is no specific environment where this problem is more
  likely to be seen.
  
  
  Platforms affected:
  MultiPlatform
  
  ****************************************************************
  PROBLEM DESCRIPTION:
  When a thread ends in the IBM MQ amqzlaa0 "agent" process then
  an attempt is made to reuse the thread as an optimization which
  avoids the expense of terminating and then creating a new
  thread.  A timing window was discovered where if an interprocess
  communication "shutdown" command was
  received while markign the thread for reuse, this could cause
  the thread to enter a hard loop.
  

Problem conclusion

• The code has been changed to add an artificial sleep in the
  event that a
  shutdown command is received.  This change prevents the thread
  from
  saturating the CPU in the event of a hard loop occurring.  A
  second change has
  been made to detect and break out of a hard loop in the affected
  section of code.
  
  ---------------------------------------------------------------
  The fix is targeted for delivery in the following PTFs:
  
  Version    Maintenance Level
  v9.2 LTS   9.2.0.20
  v9.3 LTS   9.3.0.10
  v9.x CD    9.3.4
  
  The latest available maintenance can be obtained from
  'WebSphere MQ Recommended Fixes'
  http://www-1.ibm.com/support/docview.wss?rs=171&uid=swg27006037
  
  If the maintenance level is not yet available information on
  its planned availability can be found in 'WebSphere MQ
  Planned Maintenance Release Dates'
  http://www-1.ibm.com/support/docview.wss?rs=171&uid=swg27006309
  ---------------------------------------------------------------
  

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

  MQ BASE V9.2

• Fixed component ID

  5724H7281

Applicable component levels