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simple java question

Posted on 2014-01-05
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Last Modified: 2014-01-09
An example in "android developer's cookbook", p. 57, shows how to stop a thread with the following:
If(myThread != null) {
   Thread dummy = myThread;
   MyThread = null;
   dummy.interrupt();
}

My question is, why not just do this?
If(myThread != null) {
   myThread.interrupt();
   myThread = null;
}

Are these not equivalent?

Thanks,
Mike
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Question by:thready
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3 Comments
 
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dpearson earned 1000 total points
ID: 39757752
Clearly both pieces of code are virtually identical.

The only difference is that the first one appears to be trying to play some game with the garbage collector.  The way it's written suggests some internal knowledge of the collection algorithm that might allow it to collect the resources associated with the thread if there were no references to the thread object, except for local stack variables, at the time of the interrupt being called.

I don't know enough about how Android's collector works to know if that would actually work.

If it does then certainly that behavior should have been very carefully commented in the cookbook to explain why they were doing this dance.

Even if that dance does work on Android, I think the code you wrote below is still the correct choice almost always.  The other path is at best a tiny optimization and definitely confusing to see.  It should only be used if (a) it really works and (b) recovering those extra resources is critical to the overall app.

Doug
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LVL 14

Assisted Solution

by:CPColin
CPColin earned 1000 total points
ID: 39757759
The first style would not let the object referenced by the myThread variable be collected by the garbage collector, since the dummy variable still references it. It might be trying to prevent other threads from also calling interrupt(), but, without a synchronized block, that code does not actually guarantee anything.
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Author Closing Comment

by:thready
ID: 39769872
Thanks guys.  Things that make you go hmmmm.....  :o)
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