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POJava Threads Synchronizing Problem
 

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    <p>I have the following 2 classes code that produce this result for instance:</p> <pre><code>Wainting for calculation to complete... Calculator thread says HELLO! T1 says that total is 10 Wainting for calculation to complete... Wainting for calculation to complete... </code></pre> <p>Now threads are waiting but nobody is going to notify them. How can I force the threads from T1 to T3 to run before the "Calculator thread" wake em up?</p> <pre><code>public class Calculator implements Runnable{ private int total; public int getTotal() { return total; } @Override public void run() { synchronized (this) { for (int i = 0; i &lt; 5; i++) { total += i; } System.out.println(Thread.currentThread().getName() + " says HELLO!"); notifyAll(); } } } import static java.lang.System.out; public class Reader implements Runnable{ private Calculator c; public Reader(Calculator calc) { c = calc; } public Calculator getCalculator() { return c; } public static void main(String[] args) { Calculator calc = new Calculator(); Reader read = new Reader(calc); Thread thread1 = new Thread(read); Thread thread2 = new Thread(read); Thread thread3 = new Thread(read); thread1.setName("T1"); thread2.setName("T2"); thread3.setName("T3"); thread1.start(); thread2.start(); thread3.start(); Thread calcThread = new Thread(read.getCalculator()); calcThread.setName("Calculator thread"); calcThread.start(); } } @Override public void run() { synchronized (c) { try { out.println("Wainting for calculation to complete..."); c.wait(); } catch (InterruptedException e) { e.printStackTrace(); } out.println(Thread.currentThread().getName() + " says that " + "total is " + c.getTotal()); } } } </code></pre>
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    1. COI can add Thread.sleep() after the thread3.start() but i consider that is not an appropriate solution.
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    2. COYou should never use wait/notify, but rather use the debugged utilities from java.util.concurrent and completely redesign your application accordingly. It's not clear what your real application is, so I can't really tell you what you should be using.
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    3. CO@toto : There is no reason why you shouldnt use wait/notify. They are simple and elagent primitives. java.util.concurrent classes are just wrappers over the same. I agree higher level constructs such as read and write locks, barriers and latches are offered by these classes.. but you should never really use an anvil when a simple hammer would suffice.
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