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POMultiple monitor synchronization using java thread
 

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    <p>I am writing a tiny application (something a bit bigger than "HelloWorld"). The task is to create a single producer and several consumers. The producer generates integeres and puts them in a dynamic stack (which is my monitor object), and consumers try to get those integers from stack. I do know how to create 1 producer + 1 consumer using a flag and a while with wait() inside. But how to do the same with multiple consumers. </p> <p>Please have a look at my code: </p> <pre><code>public interface StackQueueIF { void push(int value); int pop(); } public class DynamicStack implements StackQueueIF{ private volatile int stck[]; private volatile int tos; boolean valueSet = false; public DynamicStack(int size) { stck = new int[size]; tos = -1; } @Override public synchronized void push(int item) { while(valueSet){ try { wait(); } catch (InterruptedException e) { e.printStackTrace(); } } if (tos == stck.length-1) { System.out.println("---------STACK HAS BEEN DOUBLED--------"); int temp[] = new int[stck.length * 2]; for (int i = 0; i &lt; stck.length; i++) temp[i] = stck[i]; stck = temp; stck[++tos] = item; }else stck[++tos] = item; valueSet = true; notifyAll(); } @Override public synchronized int pop() { while(!valueSet){ try { wait(); } catch (InterruptedException e) { e.printStackTrace(); } } valueSet = false; notifyAll(); return stck[tos--]; } } class Producer implements Runnable{ StackQueueIF queue; String producerName; private static int counter = 0; public Producer(StackQueueIF queue, String name) { this.queue = queue; this.producerName = name; new Thread(this,producerName).start(); } @Override public void run() { while(true){ System.out.println(this.producerName + " puts " + (++counter) + " into stack"); this.queue.push(counter); try { Thread.sleep(500); } catch (InterruptedException e) { System.err.println(producerName + " interrupted"); e.printStackTrace(); } } } } class Consumer implements Runnable{ StackQueueIF queue; String consumerName; public Consumer(StackQueueIF queue, String consumerName) { this.queue = queue; this.consumerName = consumerName; new Thread(this, this.consumerName).start(); } @Override public void run() { while(true){ System.out.println(this.consumerName + " gets " + queue.pop() + " from stack"); try { Thread.sleep(500); } catch (InterruptedException e) { System.err.println(consumerName + "interrupted"); e.printStackTrace(); } } } } public class QueueTester { public static void main(String[] args) { StackQueueIF queue = new DynamicStack(10); new Producer(queue,"Producer №1"); new Consumer(queue,"Consumer №1"); new Consumer(queue,"Consumer №2"); } } </code></pre>
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    1. USgabriel angelos
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    1. COIf you run this code, you'll see that only Consumer #1 gets values from the stack while Consumer #2 gets nothing at all. That's the problem. They should both have a chance to get something from the stack or wait if it is empty.
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      1. USgabriel angelos
    2. CO+1 For using № ;)
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      1. USPeter Lawrey
 

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