Application manager: Thread management

Question

hi
i've traced sun's javatv ri and i'm facing a problem about application management.
The XletManager of the RI creates an XletThread which runs
in a while loop:
while(shouldRun) {...}
After an xlet destroys, shouldRun is set to false thus this XletThread
terminates gracefully.
The XletManager has a request producer and consumer concept.
In the while loop the thread keep looking for requests. If there is none,
it waits. If there is one, it processes the request and then waits again.
For instance, if user selects a service which contains an AUTOSTART
xlet, a request is generated and the XletThread will execute the initXlet()
implemented by the xlet. After the XletThread returns from initXlet(),
it executes startXlet().
Usually the xlet creates its own thread (UserThread) and do its work by
the thread. Thus avoid blocking XletThread too long.
Sorry for the long description and here is the problem:
If the xlet has an infinite loop in initXlet() or startXlet()
and it traps the XletThread forever, how does XletManager
terminates XletThread?
The CVM-PBP does not provide Thread.stop(), and obviously
javatv ri's XletManager does not handle such situation.
How to solve this problem if the VM is CVM-PBP?
Hence, if the UserThread is also trapped in an infinite loop,
how does XletManager identify the UserThread and also terminates it?
I've read the book "Interactive TV standards" chap 4 but the author
only states "Identifying all threads belong to an Xlet is not easy. And
even all the threads are identified, it is still difficult to terminate
them." The author does not mention how to solve the problems.
Any reply is appreciated.

Answer 1

In the general case there are no good solutions to this problem. Among the possible bad solutions are;
- test all applications before transmission so this doesn't happen
- reboot the Java VM if any calls to initXlet or startXlet (or event listeners) take more than some defined period (e.g. 10 seconds)
- have multiple XletThreads so that if one Xlet blocks in an XletThread, the implementation can still start Xlets
- have one VM instance per Xlet and kill the VM instance when an Xlet hangs
The only good choice is a JVM supporting something like JSR-121 - the Application isolation API or something like the system described in this paper from Sun;
http://java.sun.com/j2me/docs/cdc_appmgmt_wp.pdf
Of course changing your JVM may not be an option.