How to stop a thread in java 5 for a real-time system??

Question

Hi,
In Java 5, thread.stop is deprecated. We need to modify some variable to indicate that the target thread should stop running. "The target thread should check this variable regularly........"
We are currently developing a simple real-time operating system using the basic features of java. It is running on top of SunSPOT (JAVA5). My question is I need to stop a thread in a scheduler loop of a real-time operating system. We cannot check it regularly. Otherwise it is not a real-time operating system.Is there anyway else to do this?
Thanks,
Qing

Answer 1

That's rather hard to answer. You say you are writing in Java, but you're writing an OS. BUt what's executing the Java - you need a VM of some form. Is that a real-time or non-real-time VM? How it does things ultimately controls how effectively you can do what you are trying to do.
The simple answer is that Thread.stop() is deprecated and that it will not stop a thread in all situations anyway - eg trying to acquire a monitor lock. But all Thread.stop does is make an exception pending on the thread, and as the thread executes it polls to see if there is an exception pending. When this happens depends on the VM: it might be after every bytecode; it might be when the thread transitions states (eg thread-in-java, thread-in-vm, thread-in-native) - it all depends. But it is polling - just the same as checking that variable - it's just implicit in the VM rather than explicitly in your code.**
The RTSJ adds a new form of asynchronous termination requests through the AsynchronouslyInterruptedException (AIE). But it only affects code that explicitly declares that it expects AIE to occur, and there are also deferred sections where the AIE will remain pending. Writing code that can handle AIE is very difficult because the normal Java rules are "bent" and finally blocks do not get executed inside AIE-enabled code.
So as I said this is very hard to answer, it really depends what exactly you are running on and what you are trying to achieve.
** Note: some people used bytecode rewriting tools to add this kind of polling as a post-processing step. Perhaps that is something you might be able to do too.
David Holmes