API/SPI Combination + Contract Details and Examples

api/.gitignore

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+/bin

api/src/examples/java/org/reactivestreams/example/multicast/MulticastExample.java

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+package org.reactivestreams.example.multicast;
+
+import org.reactivestreams.Publisher;
+
+public class MulticastExample {
+
+    /**
+     * Each subscribe will join an existing stream.
+     * 
+     * @param args
+     * @throws InterruptedException
+     */
+    public static void main(String... args) throws InterruptedException {
+        Publisher<Stock> dataStream = new StockPricePublisher();
+
+        dataStream.subscribe(new StockPriceSubscriber(5, 500)); // 500ms on each event, infinite
+        dataStream.subscribe(new StockPriceSubscriber(10, 2000)); // 2000ms on each event, infinite
+        Thread.sleep(5000);
+        dataStream.subscribe(new StockPriceSubscriber(10, 111, 20)); // 111ms on each event, take 20
+        Thread.sleep(5000);
+        dataStream.subscribe(new StockPriceSubscriber(10, 222, 20));// 222ms on each event, take 20
+    }
+}

api/src/examples/java/org/reactivestreams/example/multicast/NeverEndingStockStream.java

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+package org.reactivestreams.example.multicast;
+
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicLong;
+
+/**
+ * Simulate a network connection that is firing data at you.
+ * <p>
+ * Purposefully not using the `Subscriber` and `Publisher` types to not confuse things with `StockPricePublisher`
+ */
+public class NeverEndingStockStream {
+
+    private static final NeverEndingStockStream INSTANCE = new NeverEndingStockStream();
+
+    private NeverEndingStockStream() {
+    }
+
+    // using array because it is far faster than list/set for iteration 
+    // which is where most of the time in the tight loop will go (... well, beside object allocation)
+    private volatile Handler[] handlers = new Handler[0];
+
+    public static synchronized void addHandler(Handler handler) {
+        if (INSTANCE.handlers.length == 0) {
+            INSTANCE.handlers = new Handler[] { handler };
+        } else {
+            Handler[] newHandlers = new Handler[INSTANCE.handlers.length + 1];
+            System.arraycopy(INSTANCE.handlers, 0, newHandlers, 0, INSTANCE.handlers.length);
+            newHandlers[newHandlers.length - 1] = handler;
+            INSTANCE.handlers = newHandlers;
+        }
+        INSTANCE.startIfNeeded();
+    }
+
+    public static synchronized void removeHandler(Handler handler) {
+        // too lazy to do the array handling
+        HashSet<Handler> set = new HashSet<>(Arrays.asList(INSTANCE.handlers));
+        set.remove(handler);
+        INSTANCE.handlers = set.toArray(new Handler[set.size()]);
+    }
+
+    public static interface Handler {
+        public void handle(Stock event);
+    }
+
+    private final AtomicBoolean running = new AtomicBoolean(false);
+    private final AtomicLong stockIndex = new AtomicLong();
+
+    private void startIfNeeded() {
+        if (running.compareAndSet(false, true)) {
+            new Thread(new Runnable() {
+
+                @Override
+                public void run() {
+                    while (handlers.length > 0) {
+                        long l = stockIndex.incrementAndGet();
+                        Stock s = new Stock(l);
+                        for (Handler h : handlers) {
+                            h.handle(s);
+                        }
+                        try {
+                            // just so it is someone sane how fast this is moving
+                            Thread.sleep(1);
+                        } catch (InterruptedException e) {
+                        }
+                    }
+                    running.set(false);
+                }
+
+            }).start();
+        }
+    }
+
+}

api/src/examples/java/org/reactivestreams/example/multicast/Stock.java

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+package org.reactivestreams.example.multicast;
+
+public class Stock {
+
+    private final long l;
+
+    public Stock(long l) {
+        this.l = l;
+    }
+
+    public long getPrice() {
+        return l;
+    }
+
+}

api/src/examples/java/org/reactivestreams/example/multicast/StockPricePublisher.java

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+package org.reactivestreams.example.multicast;
+
+import java.util.concurrent.atomic.AtomicInteger;
+
+import org.reactivestreams.Subscription;
+import org.reactivestreams.Subscriber;
+import org.reactivestreams.Publisher;
+import org.reactivestreams.example.multicast.NeverEndingStockStream.Handler;
+
+/**
+ * Publisher of stock prices from a never ending stream.
+ * <p>
+ * It will share a single underlying stream with as many subscribers as it receives.
+ * <p>
+ * If the subscriber can not keep up, it will drop (different strategies could be implemented, configurable, etc).
+ */
+public class StockPricePublisher implements Publisher<Stock> {
+
+    @Override
+    public void subscribe(final Subscriber<Stock> s) {
+        s.onSubscribe(new Subscription() {
+
+            AtomicInteger capacity = new AtomicInteger();
+            EventHandler handler = new EventHandler(s, capacity);
+
+            @Override
+            public void request(int n) {
+                if (capacity.getAndAdd(n) == 0) {
+                    // was at 0, so start up consumption again
+                    startConsuming();
+                }
+            }
+
+            @Override
+            public void cancel() {
+                System.out.println("StockPricePublisher => Cancel Subscription");
+                NeverEndingStockStream.removeHandler(handler);
+            }
+
+            public void startConsuming() {
+                NeverEndingStockStream.addHandler(handler);
+            }
+
+        });
+
+    }
+
+    private static final class EventHandler implements Handler {
+        private final Subscriber<Stock> s;
+        private final AtomicInteger capacity;
+
+        private EventHandler(Subscriber<Stock> s, AtomicInteger capacity) {
+            this.s = s;
+            this.capacity = capacity;
+        }
+
+        @Override
+        public void handle(Stock event) {
+            int c = capacity.get();
+            if (c == 0) {
+                // shortcut instead of doing decrement/increment loops while no capacity
+                return;
+            }
+            if (capacity.getAndDecrement() > 0) {
+                s.onNext(event);
+            } else {
+                // we just decremented below 0 so increment back one
+                capacity.incrementAndGet();
+            }
+        }
+    }
+
+}

api/src/examples/java/org/reactivestreams/example/multicast/StockPriceSubscriber.java

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+package org.reactivestreams.example.multicast;
+
+import java.util.concurrent.ArrayBlockingQueue;
+
+import org.reactivestreams.Subscription;
+import org.reactivestreams.Subscriber;
+
+public class StockPriceSubscriber implements Subscriber<Stock> {
+
+    private final ArrayBlockingQueue<Stock> buffer;
+    private final int delayPerStock;
+    private volatile boolean terminated = false;
+    private final int take;
+
+    public StockPriceSubscriber(int bufferSize, int delayPerStock, int take) {
+        this.buffer = new ArrayBlockingQueue<>(bufferSize);
+        this.delayPerStock = delayPerStock;
+        this.take = take;
+    }
+
+    public StockPriceSubscriber(int bufferSize, int delayPerStock) {
+        this(bufferSize, delayPerStock, -1);
+    }
+
+    @Override
+    public void onSubscribe(Subscription s) {
+        System.out.println("StockPriceSubscriber.onSubscribe => request " + buffer.remainingCapacity());
+        s.request(buffer.remainingCapacity());
+        startAsyncWork(s);
+    }
+
+    @Override
+    public void onNext(Stock t) {
+        buffer.add(t);
+    }
+
+    @Override
+    public void onError(Throwable t) {
+        terminated = true;
+        throw new RuntimeException(t);
+    }
+
+    @Override
+    public void onComplete() {
+        terminated = true;
+    }
+
+    private void startAsyncWork(final Subscription s) {
+        System.out.println("StockPriceSubscriber => Start new worker thread");
+        /* don't write real code like this! just for quick demo */
+        new Thread(new Runnable() {
+            public void run() {
+                int received = 0;
+
+                while (!terminated) {
+                    Stock v = buffer.poll();
+                    try {
+                        Thread.sleep(delayPerStock);
+                    } catch (Exception e) {
+                        e.printStackTrace();
+                    }
+                    if (buffer.size() < 3) {
+                        s.request(buffer.remainingCapacity());
+                    }
+                    if (v != null) {
+                        received++;
+                        System.out.println("StockPriceSubscriber[" + delayPerStock + "] => " + v.getPrice());
+                        if (take > 0 && received >= take) {
+                            s.cancel();
+                            terminated = true;
+                        }
+                    }
+                }
+            }
+        }).start();
+    }
+
+}

api/src/examples/java/org/reactivestreams/example/unicast/InfiniteIncrementNumberPublisher.java

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+package org.reactivestreams.example.unicast;
+
+import java.util.concurrent.atomic.AtomicInteger;
+
+import org.reactivestreams.Subscription;
+import org.reactivestreams.Subscriber;
+import org.reactivestreams.Publisher;
+
+class InfiniteIncrementNumberPublisher implements Publisher<Integer> {
+
+    @Override
+    public void subscribe(final Subscriber<Integer> s) {
+
+        final AtomicInteger i = new AtomicInteger();
+
+        Subscription subscription = new Subscription() {
+
+            AtomicInteger capacity = new AtomicInteger();
+
+            @Override
+            public void request(int n) {
+                System.out.println("signalAdditionalDemand => " + n);
+                if (capacity.getAndAdd(n) == 0) {
+                    // start sending again if it wasn't already running
+                    send();
+                }
+            }
+
+            private void send() {
+                System.out.println("send => " + capacity.get());
+                // this would normally use an eventloop, actor, whatever
+                new Thread(new Runnable() {
+
+                    public void run() {
+                        do {
+                            s.onNext(i.incrementAndGet());
+                        } while (capacity.decrementAndGet() > 0);
+                    }
+                }).start();
+            }
+
+            @Override
+            public void cancel() {
+                capacity.set(-1);
+            }
+
+        };
+
+        s.onSubscribe(subscription);
+
+    }
+}

api/src/examples/java/org/reactivestreams/example/unicast/NumberSubscriberThatHopsThreads.java

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+package org.reactivestreams.example.unicast;
+
+import java.util.concurrent.ArrayBlockingQueue;
+
+import org.reactivestreams.Subscription;
+import org.reactivestreams.Subscriber;
+
+class NumberSubscriberThatHopsThreads implements Subscriber<Integer> {
+
+    final int BUFFER_SIZE = 10;
+    private final ArrayBlockingQueue<Integer> buffer = new ArrayBlockingQueue<>(BUFFER_SIZE);
+    private volatile boolean terminated = false;
+    private final String token;
+
+    NumberSubscriberThatHopsThreads(String token) {
+        this.token = token;
+    }
+
+    @Override
+    public void onSubscribe(Subscription s) {
+        System.out.println("onSubscribe => request " + BUFFER_SIZE);
+        s.request(BUFFER_SIZE);
+        startAsyncWork(s);
+    }
+
+    @Override
+    public void onNext(Integer t) {
+        buffer.add(t);
+    }
+
+    @Override
+    public void onError(Throwable t) {
+        terminated = true;
+        throw new RuntimeException(t);
+    }
+
+    @Override
+    public void onComplete() {
+        terminated = true;
+    }
+
+    private void startAsyncWork(final Subscription s) {
+        System.out.println("**** Start new worker thread");
+        /* don't write real code like this! just for quick demo */
+        new Thread(new Runnable() {
+            public void run() {
+                while (!terminated) {
+                    Integer v = buffer.poll();
+                    try {
+                        Thread.sleep(100);
+                    } catch (Exception e) {
+                        e.printStackTrace();
+                    }
+                    if (buffer.size() < 3) {
+                        s.request(BUFFER_SIZE - buffer.size());
+                    }
+                    if (v != null) {
+                        System.out.println(token + " => Did stuff with v: " + v);
+                    }
+                }
+            }
+        }).start();
+    }
+}