concurrency7ProducerConsumer

1package pkg7concurrency;2 3/*4 * concurrency7ProducerConsumer.java5 * ---------------------6 * The classic producer/consumer problem solved with a BlockingQueue, which7 * handles all the waiting/signaling for you (no manual wait/notify).8 *9 * BlockingQueue.put() blocks when full; take() blocks when empty.10 * A "poison pill" signals consumers to stop.11 */12import java.util.concurrent.*;13import java.util.concurrent.atomic.AtomicInteger;14 15public class concurrency7ProducerConsumer {16 17    private static final int POISON = -1;18 19    public static void main(String[] args) throws InterruptedException {20        BlockingQueue<Integer> queue = new ArrayBlockingQueue<>(10);  // bounded buffer21        AtomicInteger consumedSum = new AtomicInteger();22        int items = 20, consumers = 3;23 24        // Producer25        Thread producer = new Thread(() -> {26            try {27                for (int i = 1; i <= items; i++) queue.put(i);   // blocks if full28                for (int c = 0; c < consumers; c++) queue.put(POISON);  // stop signals29            } catch (InterruptedException ignored) {}30        }, "producer");31 32        // Consumers33        Thread[] cons = new Thread[consumers];34        for (int c = 0; c < consumers; c++) {35            cons[c] = new Thread(() -> {36                try {37                    while (true) {38                        int v = queue.take();                    // blocks if empty39                        if (v == POISON) return;40                        consumedSum.addAndGet(v);41                    }42                } catch (InterruptedException ignored) {}43            }, "consumer-" + c);44        }45 46        producer.start();47        for (Thread t : cons) t.start();48        producer.join();49        for (Thread t : cons) t.join();50 51        int expected = items * (items + 1) / 2;   // 1..20 sum = 21052        System.out.println("consumed sum = " + consumedSum.get() + " (expected " + expected + ")");53        System.out.println("match: " + (consumedSum.get() == expected));54    }55}