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PO
 

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    <p>My approach to multi-threaded problems is to break up the code that the thread will run and then determine how many threads will run that code and if the access any variables that other threads could potentially use. </p> <p>In the example, there are 3 threads. The <code>main</code> thread calls <code>new Threads1().go();</code>, creates <code>r1</code>, and starts 2 more threads, <code>new Thread(r1).start();</code> and <code>new Thread(r1).start();</code>. Now that we know how many threads we can track what they are going to do.</p> <p>The <code>main</code> thread is going to die after it returns from <code>go()</code>.</p> <p>The other 2 threads are each going to enter the <code>run()</code> method of the <code>Runner</code> object, <code>r1</code>. Now what we also know is that each thread will execute <code>run()</code>. So lets look at what <code>run()</code> does. It has a <code>for</code> loop that prints output each time it executes the loop. Therefore the call to <code>run()</code> will print <code>4</code> times. So 2 threads each thread will print <code>4</code> times. Therefore the output cannot have any more than <code>8</code> numbers.</p> <p>Regarding what those digits will be is not really going to be possible since the <code>Runner</code> instance will be the same for each thread the <code>x</code> variable can change based on the other thread that is also calling <code>run()</code>. Therefore all you need to determine is, is the sequence of digits possible? The answer to that question is 'yes' for A and C. This is due to the fact that you have no idea when each thread will be preempted by the other and since during the loop there is a local copy being made, you could get some very unique orderings.</p> <p>As mentioned below by SB the, option B even though it has 8 outputs it is not possible. Try and come up with a thread sequence to create that output.</p>
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    1. POHow do you think through and predict the output of a threading question like this?
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    1. COhow is it yes for B?
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    2. COOh wow. That is a good call. My bad. I will correct that. Great catch.
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    3. COthe answer could be A, B, or even C depending on what priority each thread has and when each instruction is executed. My best guess would be to answer A as it is the only answer that display some repeating numbers interlaced, meaning that both thread are being executed in parallel. But any of the first 3 could be justified.
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      1. USYanick Rochon
 

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