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POQuestions on Concurrency from Java Guide
 

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  1. POQuestions on Concurrency from Java Guide
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    <p>So I've been reading on concurrency and have some questions on the way (<a href="http://docs.oracle.com/javase/tutorial/essential/concurrency/index.html" rel="nofollow">guide I followed</a> - though I'm not sure if its the best source):</p> <ol> <li>Processes vs. Threads: Is the difference basically that a process is the program as a whole while a thread can be a (small) part of a program?</li> <li>I am not exactly sure why there is a interrupted() method and a InterruptedException. Why should the interrupted() method even be used? It just seems to me that Java just adds an extra layer of indirection.</li> <li>For synchronization (and specifically about the one in that link), how does adding the synchronize keyword even fix the problem? I mean, if Thread A gives back its incremented c and Thread B gives back the decremented c and store it to some other variable, I am not exactly sure how the problem is solved. I mean this may be answering my own question, but is it supposed to be assumed that after one of the threads return an answer, terminate? And if that is the case, why would adding synchronize make a difference?</li> <li>I read (from some random PDF) that if you have two Threads start() subsequently, you cannot guarantee that the first thread will occur before the second thread. How would you guarantee it, though?</li> <li>In synchronization statements, I am not completely sure whats the point of adding synchronized within the method. What is wrong with leaving it out? Is it because one expects both to mutate separately, but to be obtained together? Why not just have the two non-synchronized?</li> <li>Is <em>volatile</em> just a keyword for variables and is synonymous with synchronized?</li> <li>In the deadlock problem, how does synchronize even help the situation? What makes this situation different from starting two threads that change a variable?</li> <li>Moreover, where is the "wait"/lock for the other person to bowBack? I would have thought that bow() was blocked, not bowBack().</li> </ol> <p>I'll stop here because I think if I went any further without these questions answered, I will not be able to understand the later lessons.</p>
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    1. COYou said this: `I'll stop here because I think if I went any further without these questions answered, I will not be able to understand the later lessons.` Good point - but you need to carry it further because what you've posted here is too broad. Start at #1 and just #1. Don't move on to #2 until you understand #1. Take the time to make a sample program or two. If you have any questions with that specifically then ask a single question; instead of asking 8 of them at once.
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    2. COI can answer some of those: 1: yes, exactly. Think of threads as threads and programs as quilts. 2: Because sometimes you want to cut a thread off from some things, like sleeping. `interruped()` tells you if the thread has been interrupted. 3: Synchronization means only 1 thing can access the block at a time. Everything else has to wait. 4: You would guarantee it by waiting till the first thread has indicated it has started. 5:As I said before, the JVM can only have one thread inside each synchronized block. Use this for things that can't be simulatneously edited. That's all I know :D
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    3. CORead [Java Concurrency in Practice](http://jcip.net)
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