Network Deployment (Distributed operating systems), v8.0 > Troubleshoot and support > Configure the hang detection policy
Hung threads in Java Platform, Enterprise Edition applications
WAS monitors thread activity and performs diagnostic actions if one has become inactive. When WebSphere detects that a thread has been active longer than the time defined by the thread monitor threshold, the application server takes the following actions:
- Logs a warning in the WAS log that indicates the name of the thread that is hung and how long it has already been active. The following message is written to the log:
WSVR0605W: Thread threadname has been active for hangtime and may be hung. There are totalthreads threads in total in the server that may be hung.
where: threadname is the name that appears in a JVM thread dump, hangtime gives an approximation of how long the thread has been active and totalthreads gives an overall assessment of the system threads.
- Issues a Java Management Extensions (JMX) notification. This notification enables third-party tools to catch the event and take appropriate action, such as triggering a JVM thread dump of the server, or issuing an electronic page or email. The following JMX notification events are defined in the com.ibm.websphere.management.NotificationConstants class:
- TYPE_THREAD_MONITOR_THREAD_HUNG This event is triggered by the detection of a (potentially) hung thread.
- TYPE_THREAD_MONITOR_THREAD_CLEAR This event is triggered if a thread that was previously reported as hung completes its work. Consult the section on false alarms for more information.
- Triggers changes in the PMI data counters. These PMI data counters are used by various tools, such as the Tivoli Performance Viewer, to provide a performance analysis.
- Triggers changes in the PMI data counters. These PMI data counters are used by various tools, such as the Tivoli Performance Viewer, to provide a performance analysis.
False Alarms
If the work actually completes, a second set of messages, notifications and PMI events is produced to identify the false alarm. The following message is written to the log:
WSVR0606W: Thread threadname was previously reported to be hung but has completed. It was active for approximately hangtime. There are totalthreads threads in total in the server that still may be hung.
where threadname is the name that appears in a JVM thread dump, hangtime gives an approximation of how long the thread has been active and totalthreads gives an overall assessment of the system threads.
Automatic adjustment of the hang time threshold
If the thread monitor determines too many false alarms are issued (determined by the number of pairs of hang and clear messages), it can automatically adjust the threshold. When this adjustment occurs, the following message is written to the log:
WSVR0607W: Too many thread hangs have been falsely reported. The hang threshold is now being set to thresholdtime.
where thresholdtime is the time (in seconds) in which a thread can be active before it is considered hung. You can prevent WAS from automatically adjusting the hang time threshold. See Configure the hang detection policy
Configure the hang detection policy
Monitor performance with Tivoli Performance Viewer
Example: Adjusting the thread monitor to affect server hang detection