Thursday, January 10, 2008

interrupt() -- 2 real threads, 1 Thread object

myThread.interrupt() methods involves 2 real threads. As another post mentions, each real thread has a rather poor handle on it in the form of a Thread object. In this case, one such object is involved -- the target thread object. So the real and fake thread thingies involved are

A) the real sender thread (thread23) -- the call stack containing the method (sendInterruptMsg()) that sends the interrupt() message
C) the target thread object -- myThread object.
B) the real target thread -- the thread accessible by myThread object, potentially executing some blocking method.

void sendInterruptMsg(){ // runs in thread23
myThread.interrupt()
}

Note, in this case, the thread object is not a poor handle on the real thread, but a solid handle on the real thread. There are very few such useful instance methods in a thread object though, that's why i say thread objects are a poor handle on the real threads.

Next thing to learn is the exception thrown as a result of the interrupt.

Q: Which real thread (stack) will generate and receive the exception?
A: (B), not C, since the thread object is NOT a call stack and can't deal with exceptions.

Q: which method will throw it?
A: the interrupted method. Note all other exceptions are triggered by actions by the call stack itself -- synchronous. But InterruptedException is triggered by a lightning strike -- asynchronous.

Q: what methods can be interrupted this way?
A: blocking methods. Any method that can be interrupted must declare "throws InterruptedException". Actually there are very few such methods, so they are important -- static Thread.sleep, myObject.wait()...

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