Adventures with Reactive Streams

In today's world, more and more people are creating software that is expected to run at large scale. Large scale and cost-effectiveness often lead programmers to asynchronous programming models for handling vertical scalability concerns. Creating an asynchronous application on the JVM is nontrivial and often leads to disparate abstractions. Reactive Streams is one such abstraction that is widely accepted on the JVM today. This presentation is a deep dive into what it takes to implement the Reactive Streams specifications. It delves into various trade-offs that library developers have to consider while implementing Reactive Streams and which aspects of practical applications make such trade-offs easier.

Transcript

1. Adventures with
   Reactive Streams
   @NiteshKant
   Nitesh Kant @jovoordeckers
   Jo Voordeckers
   

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2. Image source: https://interestingengineering.com/12-of-the-worlds-most-fascinating-dams
   

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3. Image source: https://en.wikipedia.org/wiki/Oroville_Dam_crisis
   

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4. @NiteshKant
   Nitesh Kant @jovoordeckers
   Jo Voordeckers
   

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5. Find my friends
   GET /friends?id=3 HTTP/1.1
   

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6. Find my friends
   GET /friends?id=3 HTTP/1.1 getFriendsCsv()
   HTTP/1.1 200 OK
   Nitesh, Kant, SF
   Jo, Voordeckers, SF
   …
   

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7. Find my friends
   GET /friends?id=3 HTTP/1.1 getFriendsCsv()
   transformToJson()
   HTTP/1.1 200 OK
   Nitesh, Kant, SF
   Jo, Voordeckers, SF
   …
   HTTP/1.1 200 OK
   {First: Nitesh, Last: Kant, Location: SF}
   {First: Jo, Last: Voordeckers, Location: SF}
   …
   

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8. Find my friends
   GET /friends?id=3 HTTP/1.1 getFriendsCsv()
   transformToJson()
   HTTP/1.1 200 OK
   {First: Nitesh, Last: Kant, Location: SF}
   {First: Jo, Last: Voordeckers, Location: SF}
   …
   response.send()
   HTTP/1.1 200 OK
   Nitesh, Kant, SF
   Jo, Voordeckers, SF
   …
   HTTP/1.1 200 OK
   {First: Nitesh, Last: Kant, Location: SF}
   {First: Jo, Last: Voordeckers, Location: SF}
   …
   

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9. HTTP/1.1 200 OK
   {First: Nitesh, Last: Kant, Location: SF}
   {First: Jo, Last: Voordeckers, Location: SF}
   …
   response.send()
   Find my friends
   getFriendsCsv()
   HTTP/1.1 200 OK
   Nitesh, Kant, SF
   Jo, Voordeckers, SF
   … 011101100
   101110011
   101100101
   110011100
   101110111
   011001101
   011101100
   101110011
   101100101
   110011100
   101110111
   011001101
   011101100
   101110011
   101100101
   110011100
   101110111
   011001101
   011101100
   101110011
   101100101
   110011100
   101110111
   011001101
   011101100
   101110011
   101100101
   110011100
   101110111
   011001101
   

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10. Find my friends
    GET /friends?id=3 HTTP/1.1
    getFriendsCsv()
    HTTP/1.1 200 OK
    Nitesh, Kant, SF
    Jo, Voordeckers, SF
    …
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    response.send()
    

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11. Find my friends
    GET /friends?id=3 HTTP/1.1
    getFriendsCsv()
    response.send()
    HTTP/1.1 200 OK
    Nitesh, Kant, SF
    Jo, Voordeckers, SF
    …
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    response.send()
    

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12. Find my friends
    GET /friends?id=3 HTTP/1.1
    getFriendsCsv()
    response.send()
    HTTP/1.1 200 OK
    Nitesh, Kant, SF
    Jo, Voordeckers, SF
    …
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    response.send()
    

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13. Find my friends
    GET /friends?id=3 HTTP/1.1
    getFriendsCsv()
    response.send()
    HTTP/1.1 200 OK
    Nitesh, Kant, SF
    Jo, Voordeckers, SF
    …
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    response.send()
    

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14. Find my friends
    GET /friends?id=3 HTTP/1.1
    getFriendsCsv()
    response.send()
    HTTP/1.1 200 OK
    Nitesh, Kant, SF
    Jo, Voordeckers, SF
    …
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101 011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    response.send()
    

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15. Find my friends
    GET /friends?id=3 HTTP/1.1
    getFriendsCsv()
    HTTP/1.1 200 OK
    Nitesh, Kant, SF
    Jo, Voordeckers, SF
    …
    Producer
    Consumer
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    response.send()
    

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16. HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    Find my friends
    GET /friends?id=3 HTTP/1.1
    getFriendsCsv()
    response.send()
    HTTP/1.1 200 OK
    Nitesh, Kant, SF
    Jo, Voordeckers, SF
    …
    Producer
    Consumer Control
    
    response.send()
    

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17. I am interested in consuming data!
    Control
    
    

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18. I am interested in consuming data!
    Give me 10 items!
    Control
    
    

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19. I am interested in consuming data!
    Give me 10 items!
    I am not interested any more.
    Control
    
    

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20. Java Message Service
    https://docs.oracle.com/javaee/5/tutorial/doc/bncdx.html
    // Synchronous
    Message m = consumer.receive();
    Message m = consumer.receive(1000); // time out 1000ms
    // Asynchronous
    MessageListener myListener = new MyListener(); // void onMessage(Message message)
    consumer.setMessageListener(myListener);
    request(1)
    

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21. Java Message Service
    https://docs.oracle.com/javaee/5/tutorial/doc/bncdx.html
    // Synchronous
    Message m = consumer.receive();
    Message m = consumer.receive(1000); // time out 1000ms
    // Asynchronous
    MessageListener myListener = new MyListener(); // void onMessage(Message message)
    consumer.setMessageListener(myListener);
    flow control depends on broker
    

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22. Apache Kafka
    https://kafka.apache.org/10/javadoc/?org/apache/kafka/clients/consumer/KafkaConsumer.html
    KafkaConsumer consumer = new KafkaConsumer<>(props);
    consumer.subscribe(Arrays.asList("foo", "bar"));
    while (true) {
    ConsumerRecords records = consumer.poll(100); // time out
    for (ConsumerRecord record : records) {
    // iterate over batch
    }
    consumer.commitSync();
    }
    // Flow control
    public void pause(java.util.Collection partitions)
    public void resume(java.util.Collection partitions)
    request(n)
    

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23. Apache Kafka
    https://kafka.apache.org/10/javadoc/?org/apache/kafka/clients/consumer/KafkaConsumer.html
    KafkaConsumer consumer = new KafkaConsumer<>(props);
    consumer.subscribe(Arrays.asList("foo", "bar"));
    while (true) {
    ConsumerRecords records = consumer.poll(100); // time out
    for (ConsumerRecord record : records) {
    // iterate over batch
    }
    consumer.commitSync();
    }
    // Flow control
    public void pause(java.util.Collection partitions)
    public void resume(java.util.Collection partitions)
    additional flow control
    by topic/partition
    

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24. Apache Kafka
    JMS
    // Synchronous
    Message m = consumer.receive();
    Message m = consumer.receive(1000);
    // Asynchronous
    // void onMessage(Message message)
    MessageListener myListener = new MyListener();
    consumer.setMessageListener(myListener);
    KafkaConsumer consumer = new KafkaConsumer<>(props);
    consumer.subscribe(Arrays.asList("foo", "bar"));
    while (true) {
    ConsumerRecords records = consumer.poll(100);
    for (ConsumerRecord record : records) {
    // iterate over batch
    }
    consumer.commitSync();
    }
    // Flow control
    public void pause(java.util.Collection partitions)
    public void resume(java.util.Collection partitions)
    

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25. Apache Kafka
    JMS
    // Synchronous
    Message m = consumer.receive();
    Message m = consumer.receive(1000);
    // Asynchronous
    // void onMessage(Message message)
    MessageListener myListener = new MyListener();
    consumer.setMessageListener(myListener);
    KafkaConsumer consumer = new KafkaConsumer<>(props);
    consumer.subscribe(Arrays.asList("foo", "bar"));
    while (true) {
    ConsumerRecords records = consumer.poll(100);
    for (ConsumerRecord record : records) {
    // iterate over batch
    }
    consumer.commitSync();
    }
    // Flow control
    public void pause(java.util.Collection partitions)
    public void resume(java.util.Collection partitions)
    how do we bridge
    these APIs?
    
    

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26. Service A Service B
    

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27. Service A Service B
    cache
    ?
    

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28. Service A Service B
    cache
    Service C
    ?
    

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29. Service A Service B
    cache
    Service C
    DB
    ?
    

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30. Service A Service B
    cache
    Service C
    DB
    ?
    define contract
    for interoperability
    

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31. Service A Service B
    cache
    Service C
    DB
    write adapters for
    all the things \o/
    ?
    

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32. Service A Service B
    cache
    Service C
    DB
    write adapters for
    all the things \o/
    ?
    ✓ cancelation
    ✓ buffering
    

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33. https://github.com/reactive-streams/reactive-streams-jvm
    

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34. https://github.com/reactive-streams/reactive-streams-jvm
    

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35. Reactive Streams
    public interface Publisher {
    public void subscribe(Subscriber super T> s);
    }
    

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36. Reactive Streams
    public interface Publisher {
    public void subscribe(Subscriber super T> s);
    }
    I am interested in consuming data!
    

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37. Reactive Streams
    public interface Subscriber {
    public void onSubscribe(Subscription s);
    public void onNext(T t);
    public void onError(Throwable t);
    public void onComplete();
    }
    

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38. Reactive Streams
    public interface Subscriber {
    public void onSubscribe(Subscription s);
    public void onNext(T t);
    public void onError(Throwable t);
    public void onComplete();
    }
    Control exchange
    

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39. Reactive Streams
    public interface Subscription {
    public void request(long n);
    public void cancel();
    }
    
    

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40. Reactive Streams
    public interface Subscription {
    public void request(long n);
    public void cancel();
    }
    Give me “n” items!
    
    

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41. Reactive Streams
    public interface Subscription {
    public void request(long n);
    public void cancel();
    }
    I am not interested any more.
    
    

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42. under-specification
    Image source: https://newrepublic.com/article/118416/what-dhaka-bangladesh-traffic-capital-world-can-teach-us
    

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43. under-specification
    risk of chaos between actors
    of the interaction rules
    Image source: https://newrepublic.com/article/118416/what-dhaka-bangladesh-traffic-capital-world-can-teach-us
    

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44. under-specification
    risk of chaos between actors
    target least common denominator
    of the interaction rules
    Image source: https://newrepublic.com/article/118416/what-dhaka-bangladesh-traffic-capital-world-can-teach-us
    

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45. under-specification
    risk of chaos between actors
    target least common denominator
    systemic inefficiency
    of the interaction rules
    Image source: https://newrepublic.com/article/118416/what-dhaka-bangladesh-traffic-capital-world-can-teach-us
    

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46. subscribe()
    Publisher Subscriber
    

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47. onSubscribe()
    subscribe()
    Publisher Subscription
    onSubscribe()
    Subscriber
    

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48. request()
    onSubscribe()
    subscribe()
    Publisher Subscription
    onSubscribe()
    Subscriber
    

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49. onNext()
    onComplete()
    onError()
    onSubscribe()
    subscribe()
    Publisher Subscription
    onNext()
    onComplete()
    onError()
    onSubscribe()
    Subscriber
    request()
    

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50. sequence
    onSubscribe() onComplete()
    subscribe()
    request()
    onSubscribe()
    subscribe() onError()
    request()
    onSubscribe()
    subscribe() onNext() onError()
    request()
    onSubscribe()
    subscribe() onNext() onNext() onComplete()
    request()
    request() cancel()
    onSubscribe()
    subscribe()
    request() cancel() onNext() onComplete()
    onSubscribe()
    subscribe()
    

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51. lifecycle management
    onNext()
    X
    subscribe()
    cancel()
    request()
    subscribe() onSubscribe() onNext() request()
    X
    onNext()
    onSubscribe()
    onNext()
    request()
    onComplete()
    X
    onError()
    subscribe() X
    

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52. How difficult could it
    be to implement?
    
    

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53. Single item,
    asynchronously produced
    and delivered
    

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54. Single item, asynchronously produced and delivered (Attempt #1)
    class SingleValue implements Publisher {
    private T value;
    private boolean subscriberReady;
    private Subscriber super T> subscriber;
    @Override
    public void subscribe(Subscriber super T> s) {
    subscriber = s;
    s.onSubscribe(new Subscription() {
    @Override
    public void request(long n) {
    if (value != null) {
    s.onNext(value);
    } else {
    subscriberReady = true;
    }
    }
    @Override
    public void cancel() {
    subscriberReady = false;
    }
    });
    }
    public void emit(T value) {
    if (subscriber != null && subscriberReady) {
    subscriber.onNext(value);
    } else {
    this.value = value;
    }
    }
    }
    * This is a hot/eager source, i.e. the work has started before a Subscriber arrives
    

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55. Single item, asynchronously produced and delivered (Attempt #1)
    class SingleValue implements Publisher {
    private T value;
    private boolean subscriberReady;
    private Subscriber super T> subscriber;
    @Override
    public void subscribe(Subscriber super T> s) {
    subscriber = s;
    s.onSubscribe(new Subscription() {
    @Override
    public void request(long n) {
    if (value != null) {
    s.onNext(value);
    } else {
    subscriberReady = true;
    }
    }
    @Override
    public void cancel() {
    subscriberReady = false;
    }
    });
    }
    public void emit(T value) {
    if (subscriber != null && subscriberReady) {
    subscriber.onNext(value);
    } else {
    this.value = value;
    }
    }
    }
    * This is a hot/eager source, i.e. the work has started before a Subscriber arrives
    emit()
    subscribe()
    request()
    cancel()
    

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56. Single item, asynchronously produced and delivered (Attempt #1)
    * This is a hot/eager source, i.e. the work has started before a Subscriber arrives
    Asynchrony
    emit() subscribe() request() cancel()
    class SingleValue implements Publisher {
    private T value;
    private boolean subscriberReady;
    private Subscriber super T> subscriber;
    @Override
    public void subscribe(Subscriber super T> s) {
    subscriber = s;
    s.onSubscribe(new Subscription() {
    @Override
    public void request(long n) {
    if (value != null) {
    s.onNext(value);
    } else {
    subscriberReady = true;
    }
    }
    @Override
    public void cancel() {
    subscriberReady = false;
    }
    });
    }
    public void emit(T value) {
    if (subscriber != null && subscriberReady) {
    subscriber.onNext(value);
    } else {
    this.value = value;
    }
    }
    }
    

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57. Single item, asynchronously produced and delivered (Attempt #1)
    * This is a hot/eager source, i.e. the work has started before a Subscriber arrives
    Asynchrony
    emit()
    subscribe() request() cancel()
    class SingleValue implements Publisher {
    private T value;
    private boolean subscriberReady;
    private Subscriber super T> subscriber;
    @Override
    public void subscribe(Subscriber super T> s) {
    subscriber = s;
    s.onSubscribe(new Subscription() {
    @Override
    public void request(long n) {
    if (value != null) {
    s.onNext(value);
    } else {
    subscriberReady = true;
    }
    }
    @Override
    public void cancel() {
    subscriberReady = false;
    }
    });
    }
    public void emit(T value) {
    if (subscriber != null && subscriberReady) {
    subscriber.onNext(value);
    } else {
    this.value = value;
    }
    }
    }
    

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58. Single item, asynchronously produced and delivered (Attempt #1)
    * This is a hot/eager source, i.e. the work has started before a Subscriber arrives
    Asynchrony
    emit()
    subscribe() request() cancel()
    class SingleValue implements Publisher {
    private T value;
    private boolean subscriberReady;
    private Subscriber super T> subscriber;
    @Override
    public void subscribe(Subscriber super T> s) {
    subscriber = s;
    s.onSubscribe(new Subscription() {
    @Override
    public void request(long n) {
    if (value != null) {
    s.onNext(value);
    } else {
    subscriberReady = true;
    }
    }
    @Override
    public void cancel() {
    subscriberReady = false;
    }
    });
    }
    public void emit(T value) {
    if (subscriber != null && subscriberReady) {
    subscriber.onNext(value);
    } else {
    this.value = value;
    }
    }
    }
    

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59. class SingleValue implements Publisher {
    private T value;
    private boolean subscriberReady;
    private Subscriber super T> subscriber;
    @Override
    public void subscribe(Subscriber super T> s) {
    subscriber = s;
    s.onSubscribe(new Subscription() {
    @Override
    public void request(long n) {
    if (value != null) {
    s.onNext(value);
    } else {
    subscriberReady = true;
    }
    }
    @Override
    public void cancel() {
    subscriberReady = false;
    }
    });
    }
    public void emit(T value) {
    if (subscriber != null && subscriberReady) {
    subscriber.onNext(value);
    } else {
    this.value = value;
    }
    }
    }
    Single item, asynchronously produced and delivered (Attempt #1)
    * This is a hot/eager source, i.e. the work has started before a Subscriber arrives
    Asynchrony
    emit()
    subscribe() request() cancel()
    

    View Slide

60. Single item, asynchronously produced and delivered (Attempt #1)
    * This is a hot/eager source, i.e. the work has started before a Subscriber arrives
    Concurrency
    emit()
    subscribe() request() cancel()
    class SingleValue implements Publisher {
    private T value;
    private boolean subscriberReady;
    private Subscriber super T> subscriber;
    @Override
    public void subscribe(Subscriber super T> s) {
    subscriber = s;
    s.onSubscribe(new Subscription() {
    @Override
    public void request(long n) {
    if (value != null) {
    s.onNext(value);
    } else {
    subscriberReady = true;
    }
    }
    @Override
    public void cancel() {
    subscriberReady = false;
    }
    });
    }
    public void emit(T value) {
    if (subscriber != null && subscriberReady) {
    subscriber.onNext(value);
    } else {
    this.value = value;
    }
    }
    }
    

    View Slide

61. Single item, asynchronously produced and delivered (Attempt #1)
    * This is a hot/eager source, i.e. the work has started before a Subscriber arrives
    Concurrency
    emit()
    subscribe() request() cancel()
    class SingleValue implements Publisher {
    private T value;
    private boolean subscriberReady;
    private Subscriber super T> subscriber;
    @Override
    public void subscribe(Subscriber super T> s) {
    subscriber = s;
    s.onSubscribe(new Subscription() {
    @Override
    public void request(long n) {
    if (value != null) {
    s.onNext(value);
    } else {
    subscriberReady = true;
    }
    }
    @Override
    public void cancel() {
    subscriberReady = false;
    }
    });
    }
    public void emit(T value) {
    if (subscriber != null && subscriberReady) {
    subscriber.onNext(value);
    } else {
    this.value = value;
    }
    }
    }
    

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62. Single item, asynchronously produced and delivered (Attempt #1)
    * This is a hot/eager source, i.e. the work has started before a Subscriber arrives
    Concurrency
    emit()
    subscribe() request() cancel()
    class SingleValue implements Publisher {
    private T value;
    private boolean subscriberReady;
    private Subscriber super T> subscriber;
    @Override
    public void subscribe(Subscriber super T> s) {
    subscriber = s;
    s.onSubscribe(new Subscription() {
    @Override
    public void request(long n) {
    if (value != null) {
    s.onNext(value);
    } else {
    subscriberReady = true;
    }
    }
    @Override
    public void cancel() {
    subscriberReady = false;
    }
    });
    }
    public void emit(T value) {
    if (subscriber != null && subscriberReady) {
    subscriber.onNext(value);
    } else {
    this.value = value;
    }
    }
    }
    

    View Slide

63. Single item, asynchronously produced and delivered (Attempt #1)
    * This is a hot/eager source, i.e. the work has started before a Subscriber arrives
    Concurrency
    emit()
    subscribe() request() cancel()
    X
    class SingleValue implements Publisher {
    private T value;
    private boolean subscriberReady;
    private Subscriber super T> subscriber;
    @Override
    public void subscribe(Subscriber super T> s) {
    subscriber = s;
    s.onSubscribe(new Subscription() {
    @Override
    public void request(long n) {
    if (value != null) {
    s.onNext(value);
    } else {
    subscriberReady = true;
    }
    }
    @Override
    public void cancel() {
    subscriberReady = false;
    }
    });
    }
    public void emit(T value) {
    if (subscriber != null && subscriberReady) {
    subscriber.onNext(value);
    } else {
    this.value = value;
    }
    }
    }
    

    View Slide

64. Single item, asynchronously produced and delivered (Attempt #1)
    * This is a hot/eager source, i.e. the work has started before a Subscriber arrives
    Concurrency
    emit()
    subscribe() request() cancel()
    https://github.com/reactive-streams/reactive-streams-jvm#1.3
    class SingleValue implements Publisher {
    private T value;
    private boolean subscriberReady;
    private Subscriber super T> subscriber;
    @Override
    public void subscribe(Subscriber super T> s) {
    subscriber = s;
    s.onSubscribe(new Subscription() {
    @Override
    public void request(long n) {
    if (value != null) {
    s.onNext(value);
    s.onComplete();
    } else {
    subscriberReady = true;
    }
    }
    @Override
    public void cancel() {
    subscriberReady = false;
    }
    });
    }
    public void emit(T value) {
    if (subscriber != null && subscriberReady) {
    subscriber.onNext(value);
    } else {
    this.value = value;
    }
    }
    }
    

    View Slide

65. Single item, asynchronously produced and delivered (Attempt #1)
    * This is a hot/eager source, i.e. the work has started before a Subscriber arrives
    Concurrency
    emit()
    subscribe() request() cancel()
    https://github.com/reactive-streams/reactive-streams-jvm#2.7
    class SingleValue implements Publisher {
    private T value;
    private boolean subscriberReady;
    private Subscriber super T> subscriber;
    @Override
    public void subscribe(Subscriber super T> s) {
    subscriber = s;
    s.onSubscribe(new Subscription() {
    @Override
    public void request(long n) {
    if (value != null) {
    s.onNext(value);
    s.onComplete();
    } else {
    subscriberReady = true;
    }
    }
    @Override
    public void cancel() {
    subscriberReady = false;
    }
    });
    }
    public void emit(T value) {
    if (subscriber != null && subscriberReady) {
    subscriber.onNext(value);
    } else {
    this.value = value;
    }
    }
    }
    

    View Slide

66. Single item, asynchronously produced and delivered (Attempt #2)
    * This is a hot/eager source, i.e. the work has started before a Subscriber arrives
    Concurrency
    emit()
    subscribe() request() cancel()
    class SingleValue implements Publisher {
    private T value;
    private boolean subscriberReady;
    private Subscriber super T> subscriber;
    @Override
    public void subscribe(Subscriber super T> s) {
    subscriber = s;
    s.onSubscribe(new Subscription() {
    @Override
    public void request(long n) {
    if (value != null) {
    s.onNext(value);
    s.onComplete();
    } else {
    subscriberReady = true;
    }
    }
    @Override
    public void cancel() {
    subscriberReady = false;
    }
    });
    }
    public void emit(T value) {
    if (subscriber != null && subscriberReady) {
    subscriber.onNext(value);
    } else {
    this.value = value;
    }
    }
    }
    

    View Slide

67. Single item, asynchronously produced and delivered (Attempt #2)
    * This is a hot/eager source, i.e. the work has started before a Subscriber arrives
    Concurrency
    emit()
    subscribe() request() cancel()
    class SingleValue implements Publisher {
    private T value;
    private boolean subscriberReady;
    private Subscriber super T> subscriber;
    @Override
    public synchronized void subscribe(Subscriber super T> s) {
    subscriber = s;
    s.onSubscribe(new Subscription() {
    @Override
    public void request(long n) {
    if (value != null) {
    s.onNext(value);
    s.onComplete();
    } else {
    subscriberReady = true;
    }
    }
    @Override
    public void cancel() {
    subscriberReady = false;
    }
    });
    }
    public synchronized void emit(T value) {
    if (subscriber != null && subscriberReady) {
    subscriber.onNext(value);
    } else {
    this.value = value;
    }
    }
    }
    

    View Slide

68. Cost of synchronized?
    Image source: https://www.shutterstock.com/image-photo/iceberg-above-underwater-view-taken-greenland-1127373485
    

    View Slide

69. s.onNext(value);
    public synchronized void emit(T value)
    ¯\_(ツ)_/¯
    

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70. Single item, asynchronously produced and delivered (Attempt #3)
    * This is a hot/eager source, i.e. the work has started before a Subscriber arrives
    https://github.com/reactive-streams/reactive-streams-jvm#3.4
    

    View Slide

71. class SingleValue implements Publisher {
    private static final int IDLE = 0;
    private static final int REQUESTED = 1;
    private static final int EMITTED = 2;
    private T value;
    private Subscriber super T> subscriber;
    private final AtomicInteger state = new AtomicInteger(IDLE);
    @Override
    public void subscribe(Subscriber super T> s) {
    subscriber = s;
    s.onSubscribe(new Subscription() {
    @Override
    public void request(long n) {
    int old = state.getAndSet(REQUESTED);
    if (old == EMITTED) {
    s.onNext(value);
    s.onComplete();
    }
    }
    @Override
    public void cancel() {
    }
    });
    }
    public void emit(T value) {
    this.value = value;
    if (state.getAndSet(EMITTED) == REQUESTED) {
    subscriber.onNext(value);
    subscriber.onComplete();
    }
    }
    }
    Single item, asynchronously produced and delivered (Attempt #4)
    * This is a hot/eager source, i.e. the work has started before a Subscriber arrives
    State Machine
    IDLE
    EMITTED
    REQUESTED
    

    View Slide

72. Single item, asynchronously produced and delivered (Attempt #4)
    * This is a hot/eager source, i.e. the work has started before a Subscriber arrives
    State Machine
    IDLE
    class SingleValue implements Publisher {
    private static final int IDLE = 0;
    private static final int REQUESTED = 1;
    private static final int EMITTED = 2;
    private T value;
    private Subscriber super T> subscriber;
    private final AtomicInteger state = new AtomicInteger(IDLE);
    @Override
    public void subscribe(Subscriber super T> s) {
    subscriber = s;
    s.onSubscribe(new Subscription() {
    @Override
    public void request(long n) {
    int old = state.getAndSet(REQUESTED);
    if (old == EMITTED) {
    s.onNext(value);
    s.onComplete();
    }
    }
    @Override
    public void cancel() {
    }
    });
    }
    public void emit(T value) {
    this.value = value;
    if (state.getAndSet(EMITTED) == REQUESTED) {
    subscriber.onNext(value);
    subscriber.onComplete();
    }
    }
    }
    EMITTED
    REQUESTED
    

    View Slide

73. Single item, asynchronously produced and delivered (Attempt #5)
    * This is a hot/eager source, i.e. the work has started before a Subscriber arrives
    State Machine
    IDLE
    class SingleValue implements Publisher {
    private static final int IDLE = 0;
    private static final int REQUESTED = 1;
    private static final int EMITTED = 2;
    private static final int CANCELLED = 3;
    private T value;
    private Subscriber super T> subscriber;
    private final AtomicInteger state = new AtomicInteger(IDLE);
    @Override
    public void subscribe(Subscriber super T> s) {
    subscriber = s;
    s.onSubscribe(new Subscription() {
    @Override
    public void request(long n) {
    int old = state.getAndSet(REQUESTED);
    if (old == EMITTED) {
    s.onNext(value);
    s.onComplete();
    }
    }
    @Override
    public void cancel() {
    state.set(CANCELLED);
    }
    });
    }
    public void emit(T value) {
    this.value = value;
    if (state.getAndSet(EMITTED) == REQUESTED) {
    subscriber.onNext(value);
    subscriber.onComplete();
    }
    }
    }
    EMITTED
    REQUESTED
    CANCELLED
    

    View Slide

74. class SingleValue implements Publisher {
    private static final int IDLE = 0;
    private static final int REQUESTED = 1;
    private static final int EMITTED = 2;
    private static final int CANCELLED = 3;
    private T value;
    private Subscriber super T> subscriber;
    private final AtomicInteger state = new AtomicInteger(IDLE);
    @Override
    public void subscribe(Subscriber super T> s) {
    subscriber = s;
    s.onSubscribe(new Subscription() {
    @Override
    public void request(long n) {
    int old = state.getAndSet(REQUESTED);
    if (old == EMITTED) {
    s.onNext(value);
    s.onComplete();
    }
    }
    @Override
    public void cancel() {
    state.set(CANCELLED);
    }
    });
    }
    public void emit(T value) {
    this.value = value;
    if (state.getAndSet(EMITTED) == REQUESTED) {
    subscriber.onNext(value);
    subscriber.onComplete();
    }
    }
    }
    Single item, asynchronously produced and delivered (Attempt #5)
    * This is a hot/eager source, i.e. the work has started before a Subscriber arrives
    State Machine
    IDLE
    EMITTED
    REQUESTED
    CANCELLED
    

    View Slide

75. Single item, asynchronously produced and delivered (Attempt #5)
    * This is a hot/eager source, i.e. the work has started before a Subscriber arrives
    subscription.cancel();
    subscription.request(1)
    
    class SingleValue implements Publisher {
    private static final int IDLE = 0;
    private static final int REQUESTED = 1;
    private static final int EMITTED = 2;
    private static final int CANCELLED = 3;
    private T value;
    private Subscriber super T> subscriber;
    private final AtomicInteger state = new AtomicInteger(IDLE);
    @Override
    public void subscribe(Subscriber super T> s) {
    subscriber = s;
    s.onSubscribe(new Subscription() {
    @Override
    public void request(long n) {
    int old = state.getAndSet(REQUESTED);
    if (old == EMITTED) {
    s.onNext(value);
    s.onComplete();
    }
    }
    @Override
    public void cancel() {
    state.set(CANCELLED);
    }
    });
    }
    public void emit(T value) {
    this.value = value;
    if (state.getAndSet(EMITTED) == REQUESTED) {
    subscriber.onNext(value);
    subscriber.onComplete();
    }
    }
    }
    

    View Slide

76. Single item, asynchronously produced and delivered (Attempt #6)
    * This is a hot/eager source, i.e. the work has started before a Subscriber arrives
    State Machine
    IDLE
    class SingleValue implements Publisher {
    private static final int IDLE = 0;
    private static final int REQUESTED = 1;
    private static final int EMITTED = 2;
    private T value;
    private Subscriber super T> subscriber;
    private final AtomicInteger state = new AtomicInteger(IDLE);
    @Override
    public void subscribe(Subscriber super T> s) {
    subscriber = s;
    s.onSubscribe(new Subscription() {
    @Override
    public void request(long n) {
    int old = state.getAndSet(REQUESTED);
    if (old == EMITTED) {
    s.onNext(value);
    s.onComplete();
    }
    }
    @Override
    public void cancel() {
    }
    });
    }
    public void emit(T value) {
    this.value = value;
    if (state.getAndSet(EMITTED) == REQUESTED) {
    subscriber.onNext(value);
    subscriber.onComplete();
    }
    }
    }
    EMITTED
    REQUESTED
    https://github.com/reactive-streams/reactive-streams-jvm#3.6
    

    View Slide

77. Single item, asynchronously produced and delivered (Attempt #6)
    * This is a hot/eager source, i.e. the work has started before a Subscriber arrives
    class SingleValue implements Publisher {
    private static final int IDLE = 0;
    private static final int REQUESTED = 1;
    private static final int EMITTED = 2;
    private static final int CANCELLED = 3;
    private T value;
    private Subscriber super T> subscriber;
    private final AtomicInteger state = new AtomicInteger(IDLE);
    @Override
    public void subscribe(Subscriber super T> s) {
    s.onSubscribe(new Subscription() {
    @Override
    public void request(long n) {
    int old = state.getAndUpdate(val -> val == CANCELLED ? CANCELLED : REQUESTED);
    if (old == EMITTED) {
    s.onNext(value);
    s.onComplete();
    }
    }
    @Override
    public void cancel() {
    state.set(CANCELLED);
    }
    });
    subscriber = s;
    }
    public void emit(T value) {
    this.value = value;
    int old = state.getAndUpdate(val -> val == CANCELLED ? CANCELLED : EMITTED);
    if (old == REQUESTED) {
    subscriber.onNext(value);
    subscriber.onComplete();
    }
    }
    }
    

    View Slide

78. class SingleValue implements Publisher {
    private static final int IDLE = 0;
    private static final int REQUESTED = 1;
    private static final int EMITTED = 2;
    private static final int CANCELLED = 3;
    private T value;
    private Subscriber super T> subscriber;
    private final AtomicInteger state = new AtomicInteger(IDLE);
    @Override
    public void subscribe(Subscriber super T> s) {
    s.onSubscribe(new Subscription() {
    @Override
    public void request(long n) {
    int old = state.getAndUpdate(val -> val == CANCELLED ? CANCELLED : REQUESTED);
    if (old == EMITTED) {
    s.onNext(value);
    s.onComplete();
    }
    }
    @Override
    public void cancel() {
    state.set(CANCELLED);
    }
    });
    subscriber = s;
    }
    public void emit(T value) {
    this.value = value;
    int old = state.getAndUpdate(val -> val == CANCELLED ? CANCELLED : EMITTED);
    if (old == REQUESTED) {
    subscriber.onNext(value);
    subscriber.onComplete();
    }
    }
    }
    Single item, asynchronously produced and delivered (Attempt #6)
    * This is a hot/eager source, i.e. the work has started before a Subscriber arrives
    

    View Slide

79. Single item, asynchronously produced and delivered (Attempt #6)
    * This is a hot/eager source, i.e. the work has started before a Subscriber arrives
    class SingleValue implements Publisher {
    private static final int IDLE = 0;
    private static final int REQUESTED = 1;
    private static final int EMITTED = 2;
    private static final int TERMINATED = 3;
    private T value;
    private Subscriber super T> subscriber;
    private final AtomicInteger state = new AtomicInteger(IDLE);
    @Override
    public void subscribe(Subscriber super T> s) {
    s.onSubscribe(new Subscription() {
    @Override
    public void request(long n) {
    if (n <= 0 && state.getAndSet(TERMINATED) != TERMINATED) {
    s.onError(new IllegalArgumentException("Non positive request signals are illegal."));
    return;
    }
    int old = state.getAndUpdate(val -> val == TERMINATED ? TERMINATED : REQUESTED);
    if (old == EMITTED) {
    state.set(TERMINATED);
    s.onNext(value);
    s.onComplete();
    }
    }
    @Override
    public void cancel() {
    state.set(TERMINATED);
    }
    });
    subscriber = s;
    }
    public void emit(T value) {
    this.value = value;
    int old = state.getAndUpdate(val -> val == TERMINATED ? TERMINATED : EMITTED);
    if (old == REQUESTED) {
    state.set(TERMINATED);
    subscriber.onNext(value);
    subscriber.onComplete();
    }
    }
    }
    Want to see how multiple item emission
    will look like?
    
    

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80. Let’s get real …
    ✋
    

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81. response.send()
    Find my friends
    GET /friends?id=3 HTTP/1.1
    getFriendsCsv()
    response.send()
    HTTP/1.1 200 OK
    Nitesh, Kant, SF
    Jo, Voordeckers, SF
    …
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101 011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    011101100
    101110011
    101100101
    110011100
    101110111
    011001101
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    

    View Slide

82. Find my friends
    GET /friends?id=3 HTTP/1.1 getFriendsCsv()
    transformToJson()
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    response.send()
    HTTP/1.1 200 OK
    Nitesh, Kant, SF
    Jo, Voordeckers, SF
    …
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    

    View Slide

83. Find my friends
    GET /friends?id=3 HTTP/1.1 getFriendsCsv()
    transformToJson()
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    response.send()
    HTTP/1.1 200 OK
    Nitesh, Kant, SF
    Jo, Voordeckers, SF
    …
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    Socket
    Socket
    Subscriber
    Publisher
    

    View Slide

84. Find my friends
    GET /friends?id=3 HTTP/1.1 getFriendsCsv()
    transformToJson()
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    response.send()
    HTTP/1.1 200 OK
    Nitesh, Kant, SF
    Jo, Voordeckers, SF
    …
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    Socket
    Socket
    Subscriber
    Publisher
    Control
    
    

    View Slide

85. Find my friends
    GET /friends?id=3 HTTP/1.1 getFriendsCsv()
    transformToJson()
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    response.send()
    HTTP/1.1 200 OK
    Nitesh, Kant, SF
    Jo, Voordeckers, SF
    …
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    Socket
    Socket
    Subscriber
    Publisher
    subscription.request(1)
    

    View Slide

86. Find my friends
    GET /friends?id=3 HTTP/1.1 getFriendsCsv()
    transformToJson()
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    response.send()
    HTTP/1.1 200 OK
    Nitesh, Kant, SF
    Jo, Voordeckers, SF
    …
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    Socket
    Socket
    Subscriber
    Publisher
    subscription.request(1)
    Demand is required to compose
    through multiple components
    

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87. Find my friends
    GET /friends?id=3 HTTP/1.1 getFriendsCsv()
    transformToJson()
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    response.send()
    HTTP/1.1 200 OK
    Nitesh, Kant, SF
    Jo, Voordeckers, SF
    …
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    Socket
    Socket
    Subscriber
    Publisher
    subscription.cancel()
    Cancellation is required to compose
    through multiple components
    

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88. Find my friends
    GET /friends?id=3 HTTP/1.1 getFriendsCsv()
    transformToJson()
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    response.send()
    HTTP/1.1 200 OK
    Nitesh, Kant, SF
    Jo, Voordeckers, SF
    …
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    Socket
    Socket
    Subscriber
    Publisher
    Publisher client.get("friends?id=1")
    response.send(Publisher resp)
    

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89. Find my friends
    GET /friends?id=3 HTTP/1.1 getFriendsCsv()
    transformToJson()
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    response.send()
    HTTP/1.1 200 OK
    Nitesh, Kant, SF
    Jo, Voordeckers, SF
    …
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    Socket
    Socket
    Subscriber
    Publisher
    response.send(
    client.get("friends?id=1")
    );
    

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90. Find my friends
    GET /friends?id=3 HTTP/1.1 getFriendsCsv()
    transformToJson()
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    response.send()
    HTTP/1.1 200 OK
    Nitesh, Kant, SF
    Jo, Voordeckers, SF
    …
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    Socket
    Socket
    Subscriber
    Publisher
    List transformToJson(List csvs) {
    List friends;
    for (String csv : csvs) {
    friends.add(toJson(csv));
    }
    return friends;
    }
    

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91. Find my friends
    GET /friends?id=3 HTTP/1.1 getFriendsCsv()
    transformToJson()
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    response.send()
    HTTP/1.1 200 OK
    Nitesh, Kant, SF
    Jo, Voordeckers, SF
    …
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    Socket
    Socket
    Subscriber
    Publisher
    response.send(
    client.get("friends?id=1")
    );
    

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92. Find my friends
    GET /friends?id=3 HTTP/1.1 getFriendsCsv()
    transformToJson()
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    response.send()
    HTTP/1.1 200 OK
    Nitesh, Kant, SF
    Jo, Voordeckers, SF
    …
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    Socket
    Socket
    Subscriber
    Publisher
    response.send(
    client.get("friends?id=1")
    .map(csv -> toJson(csv))
    );
    

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93. Find my friends
    GET /friends?id=3 HTTP/1.1 getFriendsCsv()
    transformToJson()
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    response.send()
    HTTP/1.1 200 OK
    Nitesh, Kant, SF
    Jo, Voordeckers, SF
    …
    HTTP/1.1 200 OK
    {First: Nitesh, Last: Kant, Location: SF}
    {First: Jo, Last: Voordeckers, Location: SF}
    …
    Socket
    Socket
    Subscriber
    Publisher
    response.send(
    client.get("friends?id=1")
    .map(csv -> toJson(csv))
    );
    Function composition.
    

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94. Reactive Streams is
    not sufficient
    as an end-user API.
    
    

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95. Function Composition
    Lack of standards
    Project Reactor
    RxJava
    JDK Streams
    Akka Streams
    Kafka Streams
    

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96. Practically, most applications
    have blocking code.
    

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97. https://github.com/reactive-streams/reactive-streams-jvm#2.2
    

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98. https://github.com/reactive-streams/reactive-streams-jvm#2.2
    Embracing this reality is necessary…
    

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99. Not everything is a stream
    Publisher getUser(String id);
    

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100. Not everything is a stream
     Publisher getUser(String id);
     Publisher fireAndForget(String log);
     

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101. Not everything is a stream
     Publisher getUser(String id);
     
     Publisher fireAndForget(String log);
     Publisher request(HttpRequest request);
     

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102. Reactive Streams
     HTTP Kafka
     Cassandra
     RPC Redis
     ()
     Function Composition
     Not everything is a stream
     Blocking safety
     

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103. Image source: http://sciencemeetsfood.org/team-work/
     

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104. Thank You!
     @NiteshKant
     Nitesh Kant @jovoordeckers
     Jo Voordeckers
     +
     

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