Fixes are available
16.0.0.3: WebSphere Application Server Liberty 16.0.0.3
16.0.0.4: WebSphere Application Server Liberty 16.0.0.4
17.0.0.1: WebSphere Application Server Liberty 17.0.0.1
17.0.0.2: WebSphere Application Server Liberty 17.0.0.2
17.0.0.3: WebSphere Application Server Liberty 17.0.0.3
17.0.0.4: WebSphere Application Server Liberty 17.0.0.4
18.0.0.1: WebSphere Application Server Liberty 18.0.0.1
18.0.0.2: WebSphere Application Server Liberty 18.0.0.2
18.0.0.3: WebSphere Application Server Liberty 18.0.0.3
18.0.0.4: WebSphere Application Server Liberty 18.0.0.4
19.0.0.1: WebSphere Application Server Liberty 19.0.0.1
19.0.0.2: WebSphere Application Server Liberty 19.0.0.2
19.0.0.3: WebSphere Application Server Liberty 19.0.0.3
19.0.0.4: WebSphere Application Server Liberty 19.0.0.4
19.0.0.5: WebSphere Application Server Liberty 19.0.0.5
19.0.0.6: WebSphere Application Server Liberty 19.0.0.6
19.0.0.7: WebSphere Application Server Liberty 19.0.0.7
19.0.0.8: WebSphere Application Server Liberty 19.0.0.8
19.0.0.9: WebSphere Application Server Liberty 19.0.0.9
19.0.0.10: WebSphere Application Server Liberty 19.0.0.10
19.0.0.11: WebSphere Application Server Liberty 19.0.0.11
19.0.0.12: WebSphere Application Server Liberty 19.0.0.12
20.0.0.1: WebSphere Application Server Liberty 20.0.0.1
20.0.0.2: WebSphere Application Server Liberty 20.0.0.2
20.0.0.3: WebSphere Application Server Liberty 20.0.0.3
20.0.0.4: WebSphere Application Server Liberty 20.0.0.4
20.0.0.5: WebSphere Application Server Liberty 20.0.0.5
20.0.0.6: WebSphere Application Server Liberty 20.0.0.6
20.0.0.7: WebSphere Application Server Liberty 20.0.0.7
20.0.0.8: WebSphere Application Server Liberty 20.0.0.8
20.0.0.9: WebSphere Application Server Liberty 20.0.0.9
20.0.0.10: WebSphere Application Server Liberty 20.0.0.10
20.0.0.11: WebSphere Application Server Liberty 20.0.0.11
20.0.0.12: WebSphere Application Server Liberty 20.0.0.12
21.0.0.3: WebSphere Application Server Liberty 21.0.0.3
21.0.0.4: WebSphere Application Server Liberty 21.0.0.4
21.0.0.5: WebSphere Application Server Liberty 21.0.0.5
21.0.0.6: WebSphere Application Server Liberty 21.0.0.6
21.0.0.7: WebSphere Application Server Liberty 21.0.0.7
21.0.0.8: WebSphere Application Server Liberty 21.0.0.8
21.0.0.9: WebSphere Application Server Liberty 21.0.0.9
21.0.0.1: WebSphere Application Server Liberty 21.0.0.1
21.0.0.2: WebSphere Application Server Liberty 21.0.0.2
21.0.0.10: WebSphere Application Server Liberty 21.0.0.10
21.0.0.11: WebSphere Application Server Liberty 21.0.0.11
21.0.0.12: WebSphere Application Server Liberty 21.0.0.12
22.0.0.1: WebSphere Application Server Liberty 22.0.0.1
22.0.0.2: WebSphere Application Server Liberty 22.0.0.2
22.0.0.3: WebSphere Application Server Liberty 22.0.0.3
22.0.0.4: WebSphere Application Server Liberty 22.0.0.4
APAR status
Closed as program error.
Error description
When checking to see if a thread is possibly hung in WebSphere Liberty, several conditions are checked, including if the number of threads is set to the max size of the pool, and when coreThreads and maxThreads are configured to be equal, this condition is always satisfied, triggering the CWWKE1200W messages. While there may be a small timing window that this condition won't occur, it may still result in the message due to other conditions for flagging hung threads.  
Local fix
Setting the attributes coreThreads and maxThreads to different values inside the <executor> tag in the server.xml works around the issue.
Problem summary
**************************************************************** * USERS AFFECTED: All users of IBM WebSphere Application * * Server Liberty * **************************************************************** * PROBLEM DESCRIPTION: CWWKE1200W Hung thread message is * * logged when the thread pool is idle. * **************************************************************** * RECOMMENDATION: * **************************************************************** In situations where the coreThreads and maxThreads setting on the executor element are the same (or very close), the server may log warning messages such as the following when the thread pool is not actually hung or deadlocked: [5/2/16 10:40:26:448 CDT] 00000019 com.ibm.ws.threading.internal.ThreadPoolController W CWWKE1200W: All threads in the Liberty default executor appear to be hung. Liberty automatically increased the number of threads from 25 to 25. However, all threads still appear to be hung. The logic that checks for hung thread conditions uses three conditions: 1) The thread pool size is at maximum. 2) That the number of completed tasks has not changed over time. 3) That the incoming buffer of tasks is not empty, indicating that there is work needing to be done. When the coreThreads and maxThreads are the same, the thread pool will be maximum once the pool has created a sufficient number of threads. At that point condition 1 is satisfied (and will remain satisfied until the server is stopped). If the server is idle, then the number of completed tasks will not change over time, satisfying condition 2. If a new task is put on the queue of an idle thread pool at such a time that the server checks it for hung threads, but before a thread in the pool could complete the task, then condition 3 would also be satisfied. This would lead to the warning message getting printed in the logs even though the thread pool is not hung at all.
Problem conclusion
The fix for this APAR prevents logging of the warning message when the thread pool is not hung. The fix for this APAR is currently targeted for inclusion in fix pack 16.0.0.3. Please refer to the Recommended Updates page for delivery information: http://www.ibm.com/support/docview.wss?rs=180&uid=swg27004980
Temporary fix
There are various ways to work around this problem: 1) Do not specify the coreThreads or maxThreads settings at all. In general, the thread pool does a good job of estimating workload and adjusting the thread pool settings accordingly. For more information, see: https://developer.ibm.com/wasdev/docs/was-liberty-threading-and- why-you-probably-dont-need-to-tune-it/ 2) Do not specify the same (or too closely similar) values for coreThreads and maxThreads. 3) Enable some tasks that keep the thread pool from going idle - such as file or configuration monitoring. This will prevent the warning message by ensuring the that the thread pool continually completes tasks (incrementing the task count). 4) Ignore the message and use other methods to determine whether the server's thread pool is really hung or deadlocked.
Comments
APAR Information
APAR number
PI62609
Reported component name
WAS LIBERTY COR
Reported component ID
5725L2900
Reported release
855
Status
CLOSED PER
PE
NoPE
HIPER
NoHIPER
Special Attention
NoSpecatt / Xsystem
Submitted date
2016-05-17
Closed date
2016-06-09
Last modified date
2016-06-09
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
WAS LIBERTY COR
Fixed component ID
5725L2900
Applicable component levels
R855 PSY
UP
Document Information
Modified date:
04 May 2022