A common error in J2EE applications is a hung thread. A hung thread can result from a simple software defect (such as an infinite loop) or a more complex cause (for example, a resource deadlock). System resources, such as CPU time, might be consumed by this hung transaction when threads run unbounded code paths, such as when the code is running in an infinite loop. Alternately, a system can become unresponsive even though all resources are idle, as in a deadlock scenario. Unless an end user or a monitoring tool reports the problem, the system may remain in this degraded state indefinitely.
The hang detection option for WebSphere Application Server is turned on by default. You can configure a hang detection policy to accommodate your applications and environment so that potential hangs can be reported, providing earlier detection of failing servers. When a hung thread is detected, WebSphere Application Server notifies you so that you can troubleshoot the problem.
Using the hang detection policy, you can specify a time that is too long for a unit of work to complete. The thread monitor checks all managed threads in the system (for example, Web container threads and object request broker (ORB) threads) . Unmanaged threads, which are threads created by applications, are not monitored. For more information read Hung threads in J2EE applications .
The thread hang detection option is enabled by default. To adjust the hang detection policy values, or to disable hang detection completely:
Name: com.ibm.websphere.threadmonitor.interval Value: The frequency (in seconds) at which managed threads in the selected
application server will be interrogated.
Default: 180 seconds (three minutes).
Name: com.ibm.websphere.threadmonitor.threshold Value: The length of time (in seconds) in which a thread can be active
before it is considered hung. Any thread that is detected as
active for longer than this length of time is reported as hung.
Default: The default value is 600 seconds (ten minutes).
Name: com.ibm.websphere.threadmonitor.false.alarm.threshold
Value: The number of times (T) that false alarms can occur
before automatically increasing the threshold. It is possible that a
thread that is reported as hung eventually completes its work,
resulting in a false alarm. A large number of these events indicates
that the threshhold value is too small. The hang detection facility can
automatically respond to this situation: For every T false alarms, the
threshold T is increased by a factor of 1.5. Set the value to
zero (or less) to disable the automatic adjustment. (Link to
Detecting hung threads in J2EE applications for information on false alarms)
Default: 100
To disable the hang detection option, set the com.ibm.websphere.threadmonitor.interval property to less than or equal to zero.
Searchable topic ID: ttrb_confighangdet