Hung threads in J2EE applications


 

+

Search Tips   |   Advanced Search

 

When WebSphere detects that a thread has been active longer than the time defined by the thread monitor threshold, the appserver takes the following actions:

  1. Logs a warning indicating the name of the hung thread and how long it has been active.

    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.

  2. Issues a JMX notification, enabling 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 e-mail.

    JMX notification events are defined in...

    com.ibm.websphere.management.NotificationConstants

    The following events are available...

    • TYPE_THREAD_MONITOR_THREAD_HUNG

      Triggered by the detection of a potentially hung thread.

    • TYPE_THREAD_MONITOR_THREAD_CLEAR

      Triggered if a thread previously reported as hung completes its work.

  3. Triggers changes in the PMI data counters.

 

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 that 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.

We can prevent WAS from automatically adjusting the hang time threshold.


 

Related tasks

Configure the hang detection policy

 

Related

Example: Adjusting the thread monitor to affect server hang detection