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Ben Christensen Edge Engineering at Netflix @benjchristensen http://techblog.netflix.com/ Philly ETE - April 2015 Applying Reactive Programming with RxJava

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async + callbacks

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service composition + error handling developer productivity

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async + callbacks

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Future Future>

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Future Future>

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→ getListOfListOfMovies → forEachList → forEachMovie → getBookmark → getRating → getMetadata → getSimilars → etc

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Future Future> Future>>

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Observable Future Future> Future>>

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Everything is a Stream

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List getOrders(int customerId) List getProducts(Order order) ShippingStatus getShippingStatus(Order o, Product p) getOrders → getProducts → getShippingStatus

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List getOrders(int customerId) List getProducts(Order order) ShippingStatus getShippingStatus(Order o, Product p) getOrders → getProducts → getShippingStatus Blocking APIs

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getOrders → getProducts → getShippingStatus

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IPC via Apache HTTP Memcached Cassandra Tomcat and Servlets

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IPC via Apache HTTP Memcached Cassandra Tomcat and Servlets All Blocking

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Many things could not realistically change

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We could change our service layer

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Async Facade

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Async Facade Blocking Code Servlet Sync/Async Bridge

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Observable getOrders(int customerId) Observable getProducts(Order order) Observable getShippingStatus(Order o, Product p) getOrdersAsync → getProductsAsync → getShippingStatusAsync getOrders → getProducts → getShippingStatus

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Observable getOrders(int customerId) Observable getProducts(Order order) Observable getShippingStatus(Order o, Product p) getOrdersAsync → getProductsAsync → getShippingStatusAsync Observable APIs getOrders → getProducts → getShippingStatus

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getOrdersAsync(1) .limit(1) .flatMap(o -> { return getProductsAsync(o) .flatMap(p -> { return getShippingStatusAsync(o, p); }); }) .forEach(s -> System.out.println(Thread.currentThread() + " [Async] Shipping Status: " + s));

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getOrdersAsync(1) .limit(1) .flatMap(o -> { return getProductsAsync(o) .flatMap(p -> { return getShippingStatusAsync(o, p); }); }) .forEach(s -> System.out.println(Thread.currentThread() + " [Async] Shipping Status: " + s)); an async Observable

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getOrdersAsync(1) .limit(1) .flatMap(o -> { return getProductsAsync(o) .flatMap(p -> { return getShippingStatusAsync(o, p); }); }) .forEach(s -> System.out.println(Thread.currentThread() + " [Async] Shipping Status: " + s)); an async Observable stream

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getOrdersAsync(1) .limit(1) .flatMap(o -> { return getProductsAsync(o) .flatMap(p -> { return getShippingStatusAsync(o, p); }); }) .forEach(s -> System.out.println(Thread.currentThread() + " [Async] Shipping Status: " + s)); another async Observable stream

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getOrdersAsync(1) .limit(1) .flatMap(o -> { return getProductsAsync(o) .flatMap(p -> { return getShippingStatusAsync(o, p); }); }) .forEach(s -> System.out.println(Thread.currentThread() + " [Async] Shipping Status: " + s));

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Observable getShippingStatusAsync(Order o, Product p) ShippingStatus getShippingStatus(Order o, Product p)

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Observable getShippingStatusAsync(Order o, Product p) return Observable.defer(() -> { return Observable.just(getShippingStatus(o, p)); }).subscribeOn(Schedulers.io());

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Observable getShippingStatusAsync(Order o, Product p) return Observable.defer(() -> { return Observable.just(getShippingStatus(o, p)); }).subscribeOn(Schedulers.io());

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Observable getShippingStatusAsync(Order o, Product p) return Observable.defer(() -> { return Observable.just(getShippingStatus(o, p)); }).subscribeOn(Schedulers.io());

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Observable getShippingStatusAsync(Order o, Product p) return Observable.defer(() -> { return Observable.just(getShippingStatus(o, p)); }).subscribeOn(Schedulers.io());

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Observable getShippingStatusAsync(Order o, Product p) return Observable.defer(() -> { return Observable.just(getShippingStatus(o, p)); }).subscribeOn(Schedulers.io());

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Observable getShippingStatusAsync(Order o, Product p) return Observable.defer(() -> { return Observable.just(getShippingStatus(o, p)); }).subscribeOn(Schedulers.io());

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List orders = getOrders(1); Observable orders = getOrdersAsync(1);

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List orders = getOrders(1); Observable orders = getOrdersAsync(1);

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List orders = getOrders(1); Observable orders = getOrdersAsync(1);

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return Observable.defer(() -> { return Observable.from(getOrders(customerId)); }).subscribeOn(Schedulers.io()); Observable orders = getOrdersAsync(1);

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return Observable.defer(() -> { return Observable.from(getOrders(customerId)); }).subscribeOn(Schedulers.io()); Observable orders = getOrdersAsync(1);

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Observable orders = getOrdersAsync(1); return Observable.defer(() -> { return Observable.from(getOrders(customerId)); }).subscribeOn(Schedulers.io());

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return Observable.defer(() -> { return Observable.from(getOrders(customerId)); }).subscribeOn(Schedulers.io()); Observable orders = getOrdersAsync(1);

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return Observable.defer(() -> { return Observable.from(getOrders(customerId)); }).subscribeOn(Schedulers.io()); Observable orders = getOrdersAsync(1);

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Wrapped with Threads using subscribeOn

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Wrapped with Threads JDBC?

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List orders = getOrders(1); try (Connection c = Database.getConnection()) { ResultSet rs = c.createStatement() .executeQuery("select * from orders"); ArrayList orders = new ArrayList<>(); while (rs.next()) { orders.add(new Order(rs.getInt(1))); } rs.close(); return orders; } catch (Exception e) { throw new RuntimeException(e); }

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List orders = getOrders(1); try (Connection c = Database.getConnection()) { ResultSet rs = c.createStatement() .executeQuery("select * from orders"); ArrayList orders = new ArrayList<>(); while (rs.next()) { orders.add(new Order(rs.getInt(1))); } rs.close(); return orders; } catch (Exception e) { throw new RuntimeException(e); }

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Observable orders = getOrdersAsync(1); return Observable. create(o -> { try (Connection c = Database.getConnection()) { ResultSet rs = c.createStatement() .executeQuery("select * from orders"); while (rs.next() && !o.isUnsubscribed()) { o.onNext(new Order(rs.getInt(1))); } rs.close(); o.onCompleted(); } catch (Exception e) { o.onError(e); } }).subscribeOn(Schedulers.io());

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Observable orders = getOrdersAsync(1); return Observable. create(o -> { try (Connection c = Database.getConnection()) { ResultSet rs = c.createStatement() .executeQuery("select * from orders"); while (rs.next() && !o.isUnsubscribed()) { o.onNext(new Order(rs.getInt(1))); } rs.close(); o.onCompleted(); } catch (Exception e) { o.onError(e); } }).subscribeOn(Schedulers.io());

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return Observable. create(o -> { try (Connection c = Database.getConnection()) { ResultSet rs = c.createStatement() .executeQuery("select * from orders"); while (rs.next() && !o.isUnsubscribed()) { o.onNext(new Order(rs.getInt(1))); } rs.close(); o.onCompleted(); } catch (Exception e) { o.onError(e); } }).subscribeOn(Schedulers.io()); Observable orders = getOrdersAsync(1);

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return Observable. create(o -> { try (Connection c = Database.getConnection()) { ResultSet rs = c.createStatement() .executeQuery("select * from orders"); while (rs.next() && !o.isUnsubscribed()) { o.onNext(new Order(rs.getInt(1))); } rs.close(); o.onCompleted(); } catch (Exception e) { o.onError(e); } }).subscribeOn(Schedulers.io()); Observable orders = getOrdersAsync(1);

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return Observable. create(o -> { try (Connection c = Database.getConnection()) { ResultSet rs = c.createStatement() .executeQuery("select * from orders"); while (rs.next() && !o.isUnsubscribed()) { o.onNext(new Order(rs.getInt(1))); } rs.close(); o.onCompleted(); } catch (Exception e) { o.onError(e); } }).subscribeOn(Schedulers.io()); Observable orders = getOrdersAsync(1);

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return Observable. create(o -> { try (Connection c = Database.getConnection()) { ResultSet rs = c.createStatement() .executeQuery("select * from orders"); while (rs.next() && !o.isUnsubscribed()) { o.onNext(new Order(rs.getInt(1))); } rs.close(); o.onCompleted(); } catch (Exception e) { o.onError(e); } }).subscribeOn(Schedulers.io()); Observable orders = getOrdersAsync(1);

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or with “reactive pull” backpressure …

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return Observable.create(AbstractOnSubscribe. create(s -> { ResultSet rs = s.state(); try { if (rs.next()) { s.onNext(new Order(rs.getInt(1))); } else { s.onCompleted(); } } catch (SQLException e) { s.onError(e); } }, s -> { Connection c = Database.getConnection(); try { Statement stmt = c.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY, java.sql.ResultSet.CONCUR_READ_ONLY); stmt.setFetchSize(Integer.MIN_VALUE); return stmt.executeQuery("select * from orders"); } catch (SQLException e) { s.onError(e); return null; } }, rs -> rs.close() } // ignoring try/catch for slide brevity )).subscribeOn(Schedulers.io());

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return Observable.create(AbstractOnSubscribe. create(s -> { ResultSet rs = s.state(); try { if (rs.next()) { s.onNext(new Order(rs.getInt(1))); } else { s.onCompleted(); } } catch (SQLException e) { s.onError(e); } }, s -> { Connection c = Database.getConnection(); try { Statement stmt = c.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY, java.sql.ResultSet.CONCUR_READ_ONLY); stmt.setFetchSize(Integer.MIN_VALUE); return stmt.executeQuery("select * from orders"); } catch (SQLException e) { s.onError(e); return null; } }, rs -> rs.close() } // ignoring try/catch for slide brevity )).subscribeOn(Schedulers.io());

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return Observable.create(AbstractOnSubscribe. create(s -> { ResultSet rs = s.state(); try { if (rs.next()) { s.onNext(new Order(rs.getInt(1))); } else { s.onCompleted(); } } catch (SQLException e) { s.onError(e); } }, s -> { Connection c = Database.getConnection(); try { Statement stmt = c.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY, java.sql.ResultSet.CONCUR_READ_ONLY); stmt.setFetchSize(Integer.MIN_VALUE); return stmt.executeQuery("select * from orders"); } catch (SQLException e) { s.onError(e); return null; } }, rs -> rs.close() } // ignoring try/catch for slide brevity )).subscribeOn(Schedulers.io());

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return Observable.create(AbstractOnSubscribe. create(s -> { ResultSet rs = s.state(); try { if (rs.next()) { s.onNext(new Order(rs.getInt(1))); } else { s.onCompleted(); } } catch (SQLException e) { s.onError(e); } }, s -> { Connection c = Database.getConnection(); try { Statement stmt = c.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY, java.sql.ResultSet.CONCUR_READ_ONLY); stmt.setFetchSize(Integer.MIN_VALUE); return stmt.executeQuery("select * from orders"); } catch (SQLException e) { s.onError(e); return null; } }, rs -> rs.close() } // ignoring try/catch for slide brevity )).subscribeOn(Schedulers.io());

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return Observable.create(AbstractOnSubscribe. create(s -> { ResultSet rs = s.state(); try { if (rs.next()) { s.onNext(new Order(rs.getInt(1))); } else { s.onCompleted(); } } catch (SQLException e) { s.onError(e); } }, s -> { Connection c = Database.getConnection(); try { Statement stmt = c.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY, java.sql.ResultSet.CONCUR_READ_ONLY); stmt.setFetchSize(Integer.MIN_VALUE); return stmt.executeQuery("select * from orders"); } catch (SQLException e) { s.onError(e); return null; } }, rs -> rs.close() } // ignoring try/catch for slide brevity )).subscribeOn(Schedulers.io());

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return Observable.create(AbstractOnSubscribe. create(s -> { ResultSet rs = s.state(); try { if (rs.next()) { s.onNext(new Order(rs.getInt(1))); } else { s.onCompleted(); } } catch (SQLException e) { s.onError(e); } }, s -> { Connection c = Database.getConnection(); try { Statement stmt = c.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY, java.sql.ResultSet.CONCUR_READ_ONLY); stmt.setFetchSize(Integer.MIN_VALUE); return stmt.executeQuery("select * from orders"); } catch (SQLException e) { s.onError(e); return null; } }, rs -> rs.close() } // ignoring try/catch for slide brevity )).subscribeOn(Schedulers.io());

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return Observable.create(AbstractOnSubscribe. create(s -> { ResultSet rs = s.state(); try { if (rs.next()) { s.onNext(new Order(rs.getInt(1))); } else { s.onCompleted(); } } catch (SQLException e) { s.onError(e); } }, s -> { Connection c = Database.getConnection(); try { Statement stmt = c.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY, java.sql.ResultSet.CONCUR_READ_ONLY); stmt.setFetchSize(Integer.MIN_VALUE); return stmt.executeQuery("select * from orders"); } catch (SQLException e) { s.onError(e); return null; } }, rs -> rs.close() } // ignoring try/catch for slide brevity )).subscribeOn(Schedulers.io());

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return Observable.create(AbstractOnSubscribe. create(s -> { ResultSet rs = s.state(); try { if (rs.next()) { s.onNext(new Order(rs.getInt(1))); } else { s.onCompleted(); } } catch (SQLException e) { s.onError(e); } }, s -> { Connection c = Database.getConnection(); try { Statement stmt = c.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY, java.sql.ResultSet.CONCUR_READ_ONLY); stmt.setFetchSize(Integer.MIN_VALUE); return stmt.executeQuery("select * from orders"); } catch (SQLException e) { s.onError(e); return null; } }, rs -> rs.close() } // ignoring try/catch for slide brevity )).subscribeOn(Schedulers.io());

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return Observable.create(AbstractOnSubscribe. create(s -> { ResultSet rs = s.state(); try { if (rs.next()) { s.onNext(new Order(rs.getInt(1))); } else { s.onCompleted(); } } catch (SQLException e) { s.onError(e); } }, s -> { Connection c = Database.getConnection(); try { Statement stmt = c.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY, java.sql.ResultSet.CONCUR_READ_ONLY); stmt.setFetchSize(Integer.MIN_VALUE); return stmt.executeQuery("select * from orders"); } catch (SQLException e) { s.onError(e); return null; } }, rs -> rs.close() } // ignoring try/catch for slide brevity )).subscribeOn(Schedulers.io());

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return Observable.create(AbstractOnSubscribe. create(s -> { ResultSet rs = s.state(); try { if (rs.next()) { s.onNext(new Order(rs.getInt(1))); } else { s.onCompleted(); } } catch (SQLException e) { s.onError(e); } }, s -> { Connection c = Database.getConnection(); try { Statement stmt = c.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY, java.sql.ResultSet.CONCUR_READ_ONLY); stmt.setFetchSize(Integer.MIN_VALUE); return stmt.executeQuery("select * from orders"); } catch (SQLException e) { s.onError(e); return null; } }, rs -> rs.close() } // ignoring try/catch for slide brevity )).subscribeOn(Schedulers.io());

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return Observable.create(AbstractOnSubscribe. create(s -> { ResultSet rs = s.state(); try { if (rs.next()) { s.onNext(new Order(rs.getInt(1))); } else { s.onCompleted(); } } catch (SQLException e) { s.onError(e); } }, s -> { Connection c = Database.getConnection(); try { Statement stmt = c.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY, java.sql.ResultSet.CONCUR_READ_ONLY); stmt.setFetchSize(Integer.MIN_VALUE); return stmt.executeQuery("select * from orders"); } catch (SQLException e) { s.onError(e); return null; } }, rs -> rs.close() } // ignoring try/catch for slide brevity )).subscribeOn(Schedulers.io());

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return Observable.create(AbstractOnSubscribe. create(s -> { ResultSet rs = s.state(); try { if (rs.next()) { s.onNext(new Order(rs.getInt(1))); } else { s.onCompleted(); } } catch (SQLException e) { s.onError(e); } }, s -> { Connection c = Database.getConnection(); try { Statement stmt = c.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY, java.sql.ResultSet.CONCUR_READ_ONLY); stmt.setFetchSize(Integer.MIN_VALUE); return stmt.executeQuery("select * from orders"); } catch (SQLException e) { s.onError(e); return null; } }, rs -> rs.close() } // ignoring try/catch for slide brevity )).subscribeOn(Schedulers.io());

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return Observable.create(AbstractOnSubscribe. create(s -> { ResultSet rs = s.state(); try { if (rs.next()) { s.onNext(new Order(rs.getInt(1))); } else { s.onCompleted(); } } catch (SQLException e) { s.onError(e); } }, s -> { Connection c = Database.getConnection(); try { Statement stmt = c.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY, java.sql.ResultSet.CONCUR_READ_ONLY); stmt.setFetchSize(Integer.MIN_VALUE); return stmt.executeQuery("select * from orders"); } catch (SQLException e) { s.onError(e); return null; } }, rs -> rs.close() } // ignoring try/catch for slide brevity )).subscribeOn(Schedulers.io());

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return Observable.create(AbstractOnSubscribe. create(s -> { ResultSet rs = s.state(); try { if (rs.next()) { s.onNext(new Order(rs.getInt(1))); } else { s.onCompleted(); } } catch (SQLException e) { s.onError(e); } }, s -> { Connection c = Database.getConnection(); try { Statement stmt = c.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY, java.sql.ResultSet.CONCUR_READ_ONLY); stmt.setFetchSize(Integer.MIN_VALUE); return stmt.executeQuery("select * from orders"); } catch (SQLException e) { s.onError(e); return null; } }, rs -> rs.close() } // ignoring try/catch for slide brevity )).subscribeOn(Schedulers.io());

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Observable.defer Observable.from/just Observable.subscribeOn Observable.create

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Async Facade Blocking Code Servlet Sync/Async Bridge

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protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { try { // perform service composition asynchronously getShippingStatusForCustomerOrdersAsync(req.getParameter(“customerId")) .toBlocking() // block on servlet thread .forEach(status -> { try { // write output using blocking IO resp.getWriter().write(status.toString()); } catch (Exception e) { throw new RuntimeException("unable to write", e); } }); } catch (Exception e) { // toBlocking and forEach will convert async onError events into thrown exceptions resp.setStatus(500); // write and log error ... } }

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protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { try { // perform service composition asynchronously getShippingStatusForCustomerOrdersAsync(req.getParameter("customerId")) .toBlocking() // block on servlet thread .forEach(status -> { try { // write output using blocking IO resp.getWriter().write(status.toString()); } catch (Exception e) { throw new RuntimeException("unable to write", e); } }); } catch (Exception e) { // toBlocking and forEach will convert async onError events into thrown exceptions resp.setStatus(500); // write and log error ... } }

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protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { try { // perform service composition asynchronously getShippingStatusForCustomerOrdersAsync(req.getParameter("customerId")) .toBlocking() // block on servlet thread .forEach(status -> { try { // write output using blocking IO resp.getWriter().write(status.toString()); } catch (Exception e) { throw new RuntimeException("unable to write", e); } }); } catch (Exception e) { // toBlocking and forEach will convert async onError events into thrown exceptions resp.setStatus(500); // write and log error ... } }

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Observable getShippingStatusForCustomerOrdersAsync(String customerId) { return getOrdersAsync(Integer.parseInt(customerId)) .limit(1) .flatMap(o -> { return getProductsAsync(o) .flatMap(p -> { return getShippingStatusAsync(o, p); }); }); }

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Observable getShippingStatusForCustomerOrdersAsync(String customerId) { return getOrdersAsync(Integer.parseInt(customerId)) .limit(1) .flatMap(o -> { return getProductsAsync(o) .flatMap(p -> { return getShippingStatusAsync(o, p); }); }); }

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Observable getShippingStatusForCustomerOrdersAsync(String customerId) { return getOrdersAsync(Integer.parseInt(customerId)) .limit(1) .flatMap(o -> { return getProductsAsync(o) .flatMap(p -> { return getShippingStatusAsync(o, p); }); }); }

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protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { try { // perform service composition asynchronously getShippingStatusForCustomerOrdersAsync(req.getParameter("customerId")) .toBlocking() // block on servlet thread .forEach(status -> { try { // write output using blocking IO resp.getWriter().write(status.toString()); } catch (Exception e) { throw new RuntimeException("unable to write", e); } }); } catch (Exception e) { // toBlocking and forEach will convert async onError events into thrown exceptions resp.setStatus(500); // write and log error ... } }

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protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { try { // perform service composition asynchronously getShippingStatusForCustomerOrdersAsync(req.getParameter("customerId")) .toBlocking() // block on servlet thread .forEach(status -> { try { // write output using blocking IO resp.getWriter().write(status.toString()); } catch (Exception e) { throw new RuntimeException("unable to write", e); } }); } catch (Exception e) { // toBlocking and forEach will convert async onError events into thrown exceptions resp.setStatus(500); // write and log error ... } }

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protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { try { // perform service composition asynchronously getShippingStatusForCustomerOrdersAsync(req.getParameter("customerId")) .toBlocking() // block on servlet thread .forEach(status -> { try { // write output using blocking IO resp.getWriter().write(status.toString()); } catch (Exception e) { throw new RuntimeException("unable to write", e); } }); } catch (Exception e) { // toBlocking and forEach will convert async onError events into thrown exceptions resp.setStatus(500); // write and log error ... } }

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Observable.toBlocking

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Observable.toBlocking for bridging between async and sync

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So how did it go adding reactive to an existing codebase?

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First attempt took 3 tries

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What the *&!@#$^!!!

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Tech Worked …

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… but …

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Needed to relearn idiomatic solutions

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Iterable is = Arrays.asList("a", "b", "c"); ArrayList ts = new ArrayList<>(); for(String s : is) { ts.add(s + "-modified"); } // do stuff with ts ... Observable os = Observable.just("a", "b", "c"); os.map(s -> s + "-modified"); // do stuff with os ...

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try { for (String s : is) { ts.add(s + "-modified"); } } catch (Exception e) { // do something with exception } os.map(s -> s + "-modified") .onErrorResumeNext(exception -> { // do something with exception return Observable.empty(); });

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Needed to invest in documentation

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Needed to allow for time and mistakes

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Also … Unit Testing & Debugging

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Async Unit Tests

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TestSubscriber ts = new TestSubscriber<>(); Observable.interval(200, TimeUnit.MILLISECONDS) .take(5) .map(i -> { return i + " value"; }).subscribe(ts); ts.awaitTerminalEvent(); ts.assertNoErrors(); ts.assertReceivedOnNext(Arrays.asList("0 value", "1 value", "2 value", "3 value", "4 value"));

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TestSubscriber ts = new TestSubscriber<>(); Observable.interval(200, TimeUnit.MILLISECONDS) .take(5) .map(i -> { return i + " value"; }).subscribe(ts); ts.awaitTerminalEvent(); ts.assertNoErrors(); ts.assertReceivedOnNext(Arrays.asList("0 value", "1 value", "2 value", "3 value", "4 value"));

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TestSubscriber ts = new TestSubscriber<>(); Observable.interval(200, TimeUnit.MILLISECONDS) .take(5) .map(i -> { return i + " value"; }).subscribe(ts); ts.awaitTerminalEvent(); ts.assertNoErrors(); ts.assertReceivedOnNext(Arrays.asList("0 value", "1 value", "2 value", "3 value", "4 value"));

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TestSubscriber ts = new TestSubscriber<>(); Observable.interval(200, TimeUnit.MILLISECONDS) .take(5) .map(i -> { return i + " value"; }).subscribe(ts); ts.awaitTerminalEvent(); ts.assertNoErrors(); ts.assertReceivedOnNext(Arrays.asList("0 value", "1 value", "2 value", "3 value", "4 value"));

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TestSubscriber ts = new TestSubscriber<>(); Observable.interval(200, TimeUnit.MILLISECONDS) .take(5) .map(i -> { return i + " value"; }).subscribe(ts); ts.awaitTerminalEvent(); ts.assertNoErrors(); ts.assertReceivedOnNext(Arrays.asList("0 value", "1 value", "2 value", "3 value", "4 value"));

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TestSubscriber ts = new TestSubscriber<>(); Observable.interval(200, TimeUnit.MILLISECONDS) .take(5) .map(i -> { return i + " value"; }).subscribe(ts); ts.awaitTerminalEvent(); ts.assertNoErrors(); ts.assertReceivedOnNext(Arrays.asList("0 value", "1 value", "2 value", "3 value", "4 value"));

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TestScheduler test = Schedulers.test(); TestSubscriber ts = new TestSubscriber<>(); Observable.interval(200, TimeUnit.MILLISECONDS, test) .map(i -> { return i + " value"; }).subscribe(ts); test.advanceTimeBy(200, TimeUnit.MILLISECONDS); ts.assertReceivedOnNext(Arrays.asList("0 value")); test.advanceTimeTo(1000, TimeUnit.MILLISECONDS); ts.assertReceivedOnNext(Arrays.asList("0 value", "1 value”, "2 value", "3 value", "4 value"));

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TestScheduler test = Schedulers.test(); TestSubscriber ts = new TestSubscriber<>(); Observable.interval(200, TimeUnit.MILLISECONDS, test) .map(i -> { return i + " value"; }).subscribe(ts); test.advanceTimeBy(200, TimeUnit.MILLISECONDS); ts.assertReceivedOnNext(Arrays.asList("0 value")); test.advanceTimeTo(1000, TimeUnit.MILLISECONDS); ts.assertReceivedOnNext(Arrays.asList("0 value", "1 value”, "2 value", "3 value", "4 value"));

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TestScheduler test = Schedulers.test(); TestSubscriber ts = new TestSubscriber<>(); Observable.interval(200, TimeUnit.MILLISECONDS, test) .map(i -> { return i + " value"; }).subscribe(ts); test.advanceTimeBy(200, TimeUnit.MILLISECONDS); ts.assertReceivedOnNext(Arrays.asList("0 value")); test.advanceTimeTo(1000, TimeUnit.MILLISECONDS); ts.assertReceivedOnNext(Arrays.asList("0 value", "1 value”, "2 value", "3 value", "4 value"));

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TestScheduler test = Schedulers.test(); TestSubscriber ts = new TestSubscriber<>(); Observable.interval(200, TimeUnit.MILLISECONDS, test) .map(i -> { return i + " value"; }).subscribe(ts); test.advanceTimeBy(200, TimeUnit.MILLISECONDS); ts.assertReceivedOnNext(Arrays.asList("0 value")); test.advanceTimeTo(1000, TimeUnit.MILLISECONDS); ts.assertReceivedOnNext(Arrays.asList("0 value", "1 value”, "2 value", "3 value", "4 value"));

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TestScheduler test = Schedulers.test(); TestSubscriber ts = new TestSubscriber<>(); Observable.interval(200, TimeUnit.MILLISECONDS, test) .map(i -> { return i + " value"; }).subscribe(ts); test.advanceTimeBy(200, TimeUnit.MILLISECONDS); ts.assertReceivedOnNext(Arrays.asList("0 value")); test.advanceTimeTo(1000, TimeUnit.MILLISECONDS); ts.assertReceivedOnNext(Arrays.asList("0 value", "1 value”, "2 value", "3 value", "4 value"));

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TestScheduler test = Schedulers.test(); TestSubscriber ts = new TestSubscriber<>(); Observable.interval(200, TimeUnit.MILLISECONDS, test) .map(i -> { return i + " value"; }).subscribe(ts); test.advanceTimeBy(200, TimeUnit.MILLISECONDS); ts.assertReceivedOnNext(Arrays.asList("0 value")); test.advanceTimeTo(1000, TimeUnit.MILLISECONDS); ts.assertReceivedOnNext(Arrays.asList("0 value", "1 value”, "2 value", "3 value", "4 value"));

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TestScheduler test = Schedulers.test(); TestSubscriber ts = new TestSubscriber<>(); Observable.interval(200, TimeUnit.MILLISECONDS, test) .map(i -> { return i + " value"; }).subscribe(ts); test.advanceTimeBy(200, TimeUnit.MILLISECONDS); ts.assertReceivedOnNext(Arrays.asList("0 value")); test.advanceTimeTo(1000, TimeUnit.MILLISECONDS); ts.assertReceivedOnNext(Arrays.asList("0 value", "1 value”, "2 value", "3 value", "4 value"));

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TestScheduler test = Schedulers.test(); TestSubscriber ts = new TestSubscriber<>(); Observable.interval(200, TimeUnit.MILLISECONDS, test) .map(i -> { return i + " value"; }).subscribe(ts); test.advanceTimeBy(200, TimeUnit.MILLISECONDS); ts.assertReceivedOnNext(Arrays.asList("0 value")); test.advanceTimeTo(1000, TimeUnit.MILLISECONDS); ts.assertReceivedOnNext(Arrays.asList("0 value", "1 value”, "2 value", "3 value", "4 value"));

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Async Debugging is Hard

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java.lang.RuntimeException: failure! at jdbc.Test.lambda$19(Test.java:63) at jdbc.Test$$Lambda$8/888452645.call(Unknown Source) at rx.internal.operators.OperatorMap$1.onNext(OperatorMap.java:55) at rx.internal.operators.OperatorSubscribeOn$1$1$1.onNext(OperatorSubscribeOn.java:76) at rx.observables.AbstractOnSubscribe$SubscriptionState.accept(AbstractOnSubscribe.java:533) at rx.observables.AbstractOnSubscribe$SubscriptionProducer.doNext(AbstractOnSubscribe.java:367) at rx.observables.AbstractOnSubscribe$SubscriptionProducer.request(AbstractOnSubscribe.java:345) at rx.internal.operators.OperatorSubscribeOn$1$1$1$1.request(OperatorSubscribeOn.java:88) at rx.Subscriber.setProducer(Subscriber.java:177) at rx.Subscriber.setProducer(Subscriber.java:171) at rx.internal.operators.OperatorSubscribeOn$1$1$1.setProducer(OperatorSubscribeOn.java:81) at rx.observables.AbstractOnSubscribe.call(AbstractOnSubscribe.java:191) at rx.observables.AbstractOnSubscribe$LambdaOnSubscribe.call(AbstractOnSubscribe.java:274) at rx.Observable.unsafeSubscribe(Observable.java:7495) at rx.internal.operators.OperatorSubscribeOn$1$1.call(OperatorSubscribeOn.java:62) at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:55) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) at java.util.concurrent.FutureTask.run(FutureTask.java:266) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:745) Caused by: rx.exceptions.OnErrorThrowable$OnNextValue: OnError while emitting onNext value: jdbc.Product.class at rx.exceptions.OnErrorThrowable.addValueAsLastCause(OnErrorThrowable.java:98) at rx.internal.operators.OperatorMap$1.onNext(OperatorMap.java:58) ... 20 more Ugly Stacktraces

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java.lang.RuntimeException: failure! at jdbc.Test.lambda$19(Test.java:63) at jdbc.Test$$Lambda$8/888452645.call(Unknown Source) at rx.internal.operators.OperatorMap$1.onNext(OperatorMap.java:55) at rx.internal.operators.OperatorSubscribeOn$1$1$1.onNext(OperatorSubscribeOn.java:76) at rx.observables.AbstractOnSubscribe$SubscriptionState.accept(AbstractOnSubscribe.java:533) at rx.observables.AbstractOnSubscribe$SubscriptionProducer.doNext(AbstractOnSubscribe.java:367) at rx.observables.AbstractOnSubscribe$SubscriptionProducer.request(AbstractOnSubscribe.java:345) at rx.internal.operators.OperatorSubscribeOn$1$1$1$1.request(OperatorSubscribeOn.java:88) at rx.Subscriber.setProducer(Subscriber.java:177) at rx.Subscriber.setProducer(Subscriber.java:171) at rx.internal.operators.OperatorSubscribeOn$1$1$1.setProducer(OperatorSubscribeOn.java:81) at rx.observables.AbstractOnSubscribe.call(AbstractOnSubscribe.java:191) at rx.observables.AbstractOnSubscribe$LambdaOnSubscribe.call(AbstractOnSubscribe.java:274) at rx.Observable.unsafeSubscribe(Observable.java:7495) at rx.internal.operators.OperatorSubscribeOn$1$1.call(OperatorSubscribeOn.java:62) at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:55) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) at java.util.concurrent.FutureTask.run(FutureTask.java:266) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:745) Caused by: rx.exceptions.OnErrorThrowable$OnNextValue: OnError while emitting onNext value: jdbc.Product.class at rx.exceptions.OnErrorThrowable.addValueAsLastCause(OnErrorThrowable.java:98) at rx.internal.operators.OperatorMap$1.onNext(OperatorMap.java:58) ... 20 more Ugly Stacktraces

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java.lang.RuntimeException: failure! at jdbc.Test.lambda$19(Test.java:63) at jdbc.Test$$Lambda$8/888452645.call(Unknown Source) at rx.internal.operators.OperatorMap$1.onNext(OperatorMap.java:55) at rx.internal.operators.OperatorSubscribeOn$1$1$1.onNext(OperatorSubscribeOn.java:76) at rx.observables.AbstractOnSubscribe$SubscriptionState.accept(AbstractOnSubscribe.java:533) at rx.observables.AbstractOnSubscribe$SubscriptionProducer.doNext(AbstractOnSubscribe.java:367) at rx.observables.AbstractOnSubscribe$SubscriptionProducer.request(AbstractOnSubscribe.java:345) at rx.internal.operators.OperatorSubscribeOn$1$1$1$1.request(OperatorSubscribeOn.java:88) at rx.Subscriber.setProducer(Subscriber.java:177) at rx.Subscriber.setProducer(Subscriber.java:171) at rx.internal.operators.OperatorSubscribeOn$1$1$1.setProducer(OperatorSubscribeOn.java:81) at rx.observables.AbstractOnSubscribe.call(AbstractOnSubscribe.java:191) at rx.observables.AbstractOnSubscribe$LambdaOnSubscribe.call(AbstractOnSubscribe.java:274) at rx.Observable.unsafeSubscribe(Observable.java:7495) at rx.internal.operators.OperatorSubscribeOn$1$1.call(OperatorSubscribeOn.java:62) at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:55) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) at java.util.concurrent.FutureTask.run(FutureTask.java:266) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:745) Caused by: rx.exceptions.OnErrorThrowable$OnNextValue: OnError while emitting onNext value: jdbc.Product.class at rx.exceptions.OnErrorThrowable.addValueAsLastCause(OnErrorThrowable.java:98) at rx.internal.operators.OperatorMap$1.onNext(OperatorMap.java:58) ... 20 more Missing Async Call Chain

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java.lang.RuntimeException: failure! at jdbc.Test.lambda$19(Test.java:63) at jdbc.Test$$Lambda$8/888452645.call(Unknown Source) at rx.internal.operators.OperatorMap$1.onNext(OperatorMap.java:55) at rx.internal.operators.OperatorSubscribeOn$1$1$1.onNext(OperatorSubscribeOn.java:76) at rx.observables.AbstractOnSubscribe$SubscriptionState.accept(AbstractOnSubscribe.java:533) at rx.observables.AbstractOnSubscribe$SubscriptionProducer.doNext(AbstractOnSubscribe.java:367) at rx.observables.AbstractOnSubscribe$SubscriptionProducer.request(AbstractOnSubscribe.java:345) at rx.internal.operators.OperatorSubscribeOn$1$1$1$1.request(OperatorSubscribeOn.java:88) at rx.Subscriber.setProducer(Subscriber.java:177) at rx.Subscriber.setProducer(Subscriber.java:171) at rx.internal.operators.OperatorSubscribeOn$1$1$1.setProducer(OperatorSubscribeOn.java:81) at rx.observables.AbstractOnSubscribe.call(AbstractOnSubscribe.java:191) at rx.observables.AbstractOnSubscribe$LambdaOnSubscribe.call(AbstractOnSubscribe.java:274) at rx.Observable.unsafeSubscribe(Observable.java:7495) at rx.internal.operators.OperatorSubscribeOn$1$1.call(OperatorSubscribeOn.java:62) at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:55) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) at java.util.concurrent.FutureTask.run(FutureTask.java:266) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:745) Caused by: rx.exceptions.OnErrorThrowable$OnNextValue: OnError while emitting onNext value: jdbc.Product.class at rx.exceptions.OnErrorThrowable.addValueAsLastCause(OnErrorThrowable.java:98) at rx.internal.operators.OperatorMap$1.onNext(OperatorMap.java:58) ... 20 more Stack Pollution

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java.lang.RuntimeException: failure! at jdbc.Test.lambda$19(Test.java:63) at jdbc.Test$$Lambda$8/888452645.call(Unknown Source) at rx.internal.operators.OperatorMap$1.onNext(OperatorMap.java:55) at rx.internal.operators.OperatorSubscribeOn$1$1$1.onNext(OperatorSubscribeOn.java:76) at rx.observables.AbstractOnSubscribe$SubscriptionState.accept(AbstractOnSubscribe.java:533) at rx.observables.AbstractOnSubscribe$SubscriptionProducer.doNext(AbstractOnSubscribe.java:367) at rx.observables.AbstractOnSubscribe$SubscriptionProducer.request(AbstractOnSubscribe.java:345) at rx.internal.operators.OperatorSubscribeOn$1$1$1$1.request(OperatorSubscribeOn.java:88) at rx.Subscriber.setProducer(Subscriber.java:177) at rx.Subscriber.setProducer(Subscriber.java:171) at rx.internal.operators.OperatorSubscribeOn$1$1$1.setProducer(OperatorSubscribeOn.java:81) at rx.observables.AbstractOnSubscribe.call(AbstractOnSubscribe.java:191) at rx.observables.AbstractOnSubscribe$LambdaOnSubscribe.call(AbstractOnSubscribe.java:274) at rx.Observable.unsafeSubscribe(Observable.java:7495) at rx.internal.operators.OperatorSubscribeOn$1$1.call(OperatorSubscribeOn.java:62) at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:55) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) at java.util.concurrent.FutureTask.run(FutureTask.java:266) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:745) Caused by: rx.exceptions.OnErrorThrowable$OnNextValue: OnError while emitting onNext value: jdbc.Product.class at rx.exceptions.OnErrorThrowable.addValueAsLastCause(OnErrorThrowable.java:98) at rx.internal.operators.OperatorMap$1.onNext(OperatorMap.java:58) ... 20 more RxJava Tries

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Stepping Severely Limited

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Stepping Severely Limited

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Stepping Severely Limited

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orders.flatMap(o -> { return getProductsAsync(o) .doOnNext(t -> System.out.println("product: " + t)) .flatMap(p -> { return getShippingStatusAsync(o, p) .map(s -> { return s; }); }); }) Debugging via Logging

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orders.flatMap(o -> { return getProductsAsync(o) .doOnNext(t -> System.out.println("product: " + t)) .flatMap(p -> { return getShippingStatusAsync(o, p) .map(s -> { return s; }); }); }) :-( Debugging via Logging

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Async Debugging is Hard … a work in progress …

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How about once all done?

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Async Facade Blocking Code Servlet Sync/Async Bridge Observable APIs Worked Well

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public Observable handle(HttpServerRequest request, HttpServerResponse response) { // first request User object return getUser(request.getQueryParameters().get("userId")).flatMap(user -> { // then fetch personal catalog Observable> catalog = getPersonalizedCatalog(user) .flatMap(catalogList -> { return catalogList.videos().> flatMap(video -> { Observable bookmark = getBookmark(video); Observable rating = getRating(video); Observable metadata = getMetadata(video); return Observable.zip(bookmark, rating, metadata, (b, r, m) -> { return combineVideoData(video, b, r, m); }); }); }); // and fetch social data in parallel Observable> social = getSocialData(user).map(s -> { return s.getDataAsMap(); }); // merge the results return Observable.merge(catalog, social); }).flatMap(data -> { // output as SSE as we get back the data (no waiting until all is done) return response.writeAndFlush(new ServerSentEvent(SimpleJson.mapToJson(data))); }); }

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public Observable handle(HttpServerRequest request, HttpServerResponse response) { // first request User object return getUser(request.getQueryParameters().get("userId")).flatMap(user -> { // then fetch personal catalog Observable> catalog = getPersonalizedCatalog(user) .flatMap(catalogList -> { return catalogList.videos().> flatMap(video -> { Observable bookmark = getBookmark(video); Observable rating = getRating(video); Observable metadata = getMetadata(video); return Observable.zip(bookmark, rating, metadata, (b, r, m) -> { return combineVideoData(video, b, r, m); }); }); }); // and fetch social data in parallel Observable> social = getSocialData(user).map(s -> { return s.getDataAsMap(); }); // merge the results return Observable.merge(catalog, social); }).flatMap(data -> { // output as SSE as we get back the data (no waiting until all is done) return response.writeAndFlush(new ServerSentEvent(SimpleJson.mapToJson(data))); }); }

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public Observable handle(HttpServerRequest request, HttpServerResponse response) { // first request User object return getUser(request.getQueryParameters().get("userId")).flatMap(user -> { // then fetch personal catalog Observable> catalog = getPersonalizedCatalog(user) .flatMap(catalogList -> { return catalogList.videos().> flatMap(video -> { Observable bookmark = getBookmark(video); Observable rating = getRating(video); Observable metadata = getMetadata(video); return Observable.zip(bookmark, rating, metadata, (b, r, m) -> { return combineVideoData(video, b, r, m); }); }); }); // and fetch social data in parallel Observable> social = getSocialData(user).map(s -> { return s.getDataAsMap(); }); // merge the results return Observable.merge(catalog, social); }).flatMap(data -> { // output as SSE as we get back the data (no waiting until all is done) return response.writeAndFlush(new ServerSentEvent(SimpleJson.mapToJson(data))); }); }

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 Observable  b  =  Observable.flatMap({  T  t  -­‐>            Observable  r  =  ...  transform  t  ...          return  r;    }) flatMap

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 Observable  b  =  Observable.flatMap({  T  t  -­‐>            Observable  r  =  ...  transform  t  ...          return  r;    }) flatMap

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public Observable handle(HttpServerRequest request, HttpServerResponse response) { // first request User object return getUser(request.getQueryParameters().get("userId")).flatMap(user -> { // then fetch personal catalog Observable> catalog = getPersonalizedCatalog(user) .flatMap(catalogList -> { return catalogList.videos().> flatMap(video -> { Observable bookmark = getBookmark(video); Observable rating = getRating(video); Observable metadata = getMetadata(video); return Observable.zip(bookmark, rating, metadata, (b, r, m) -> { return combineVideoData(video, b, r, m); }); }); }); // and fetch social data in parallel Observable> social = getSocialData(user).map(s -> { return s.getDataAsMap(); }); // merge the results return Observable.merge(catalog, social); }).flatMap(data -> { // output as SSE as we get back the data (no waiting until all is done) return response.writeAndFlush(new ServerSentEvent(SimpleJson.mapToJson(data))); }); }

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public Observable handle(HttpServerRequest request, HttpServerResponse response) { // first request User object return getUser(request.getQueryParameters().get("userId")).flatMap(user -> { // then fetch personal catalog Observable> catalog = getPersonalizedCatalog(user) .flatMap(catalogList -> { return catalogList.videos().> flatMap(video -> { Observable bookmark = getBookmark(video); Observable rating = getRating(video); Observable metadata = getMetadata(video); return Observable.zip(bookmark, rating, metadata, (b, r, m) -> { return combineVideoData(video, b, r, m); }); }); }); // and fetch social data in parallel Observable> social = getSocialData(user).map(s -> { return s.getDataAsMap(); }); // merge the results return Observable.merge(catalog, social); }).flatMap(data -> { // output as SSE as we get back the data (no waiting until all is done) return response.writeAndFlush(new ServerSentEvent(SimpleJson.mapToJson(data))); }); }

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public Observable handle(HttpServerRequest request, HttpServerResponse response) { // first request User object return getUser(request.getQueryParameters().get("userId")).flatMap(user -> { // then fetch personal catalog Observable> catalog = getPersonalizedCatalog(user) .flatMap(catalogList -> { return catalogList.videos().> flatMap(video -> { Observable bookmark = getBookmark(video); Observable rating = getRating(video); Observable metadata = getMetadata(video); return Observable.zip(bookmark, rating, metadata, (b, r, m) -> { return combineVideoData(video, b, r, m); }); }); }); // and fetch social data in parallel Observable> social = getSocialData(user).map(s -> { return s.getDataAsMap(); }); // merge the results return Observable.merge(catalog, social); }).flatMap(data -> { // output as SSE as we get back the data (no waiting until all is done) return response.writeAndFlush(new ServerSentEvent(SimpleJson.mapToJson(data))); }); }

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public Observable handle(HttpServerRequest request, HttpServerResponse response) { // first request User object return getUser(request.getQueryParameters().get("userId")).flatMap(user -> { // then fetch personal catalog Observable> catalog = getPersonalizedCatalog(user) .flatMap(catalogList -> { return catalogList.videos().> flatMap(video -> { Observable bookmark = getBookmark(video); Observable rating = getRating(video); Observable metadata = getMetadata(video); return Observable.zip(bookmark, rating, metadata, (b, r, m) -> { return combineVideoData(video, b, r, m); }); }); }); // and fetch social data in parallel Observable> social = getSocialData(user).map(s -> { return s.getDataAsMap(); }); // merge the results return Observable.merge(catalog, social); }).flatMap(data -> { // output as SSE as we get back the data (no waiting until all is done) return response.writeAndFlush(new ServerSentEvent(SimpleJson.mapToJson(data))); }); }

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public Observable handle(HttpServerRequest request, HttpServerResponse response) { // first request User object return getUser(request.getQueryParameters().get("userId")).flatMap(user -> { // then fetch personal catalog Observable> catalog = getPersonalizedCatalog(user) .flatMap(catalogList -> { return catalogList.videos().> flatMap(video -> { Observable bookmark = getBookmark(video); Observable rating = getRating(video); Observable metadata = getMetadata(video); return Observable.zip(bookmark, rating, metadata, (b, r, m) -> { return combineVideoData(video, b, r, m); }); }); }); // and fetch social data in parallel Observable> social = getSocialData(user).map(s -> { return s.getDataAsMap(); }); // merge the results return Observable.merge(catalog, social); }).flatMap(data -> { // output as SSE as we get back the data (no waiting until all is done) return response.writeAndFlush(new ServerSentEvent(SimpleJson.mapToJson(data))); }); }

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public Observable handle(HttpServerRequest request, HttpServerResponse response) { // first request User object return getUser(request.getQueryParameters().get("userId")).flatMap(user -> { // then fetch personal catalog Observable> catalog = getPersonalizedCatalog(user) .flatMap(catalogList -> { return catalogList.videos().> flatMap(video -> { Observable bookmark = getBookmark(video); Observable rating = getRating(video); Observable metadata = getMetadata(video); return Observable.zip(bookmark, rating, metadata, (b, r, m) -> { return combineVideoData(video, b, r, m); }); }); }); // and fetch social data in parallel Observable> social = getSocialData(user).map(s -> { return s.getDataAsMap(); }); // merge the results return Observable.merge(catalog, social); }).flatMap(data -> { // output as SSE as we get back the data (no waiting until all is done) return response.writeAndFlush(new ServerSentEvent(SimpleJson.mapToJson(data))); }); }

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public Observable handle(HttpServerRequest request, HttpServerResponse response) { // first request User object return getUser(request.getQueryParameters().get("userId")).flatMap(user -> { // then fetch personal catalog Observable> catalog = getPersonalizedCatalog(user) .flatMap(catalogList -> { return catalogList.videos().> flatMap(video -> { Observable bookmark = getBookmark(video); Observable rating = getRating(video); Observable metadata = getMetadata(video); return Observable.zip(bookmark, rating, metadata, (b, r, m) -> { return combineVideoData(video, b, r, m); }); }); }); // and fetch social data in parallel Observable> social = getSocialData(user).map(s -> { return s.getDataAsMap(); }); // merge the results return Observable.merge(catalog, social); }).flatMap(data -> { // output as SSE as we get back the data (no waiting until all is done) return response.writeAndFlush(new ServerSentEvent(SimpleJson.mapToJson(data))); }); }

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public Observable handle(HttpServerRequest request, HttpServerResponse response) { // first request User object return getUser(request.getQueryParameters().get("userId")).flatMap(user -> { // then fetch personal catalog Observable> catalog = getPersonalizedCatalog(user) .flatMap(catalogList -> { return catalogList.videos().> flatMap(video -> { Observable bookmark = getBookmark(video); Observable rating = getRating(video); Observable metadata = getMetadata(video); return Observable.zip(bookmark, rating, metadata, (b, r, m) -> { return combineVideoData(video, b, r, m); }); }); }); // and fetch social data in parallel Observable> social = getSocialData(user).map(s -> { return s.getDataAsMap(); }); // merge the results return Observable.merge(catalog, social); }).flatMap(data -> { // output as SSE as we get back the data (no waiting until all is done) return response.writeAndFlush(new ServerSentEvent(SimpleJson.mapToJson(data))); }); }

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public Observable handle(HttpServerRequest request, HttpServerResponse response) { // first request User object return getUser(request.getQueryParameters().get("userId")).flatMap(user -> { // then fetch personal catalog Observable> catalog = getPersonalizedCatalog(user) .flatMap(catalogList -> { return catalogList.videos().> flatMap(video -> { Observable bookmark = getBookmark(video); Observable rating = getRating(video); Observable metadata = getMetadata(video); return Observable.zip(bookmark, rating, metadata, (b, r, m) -> { return combineVideoData(video, b, r, m); }); }); }); // and fetch social data in parallel Observable> social = getSocialData(user).map(s -> { return s.getDataAsMap(); }); // merge the results return Observable.merge(catalog, social); }).flatMap(data -> { // output as SSE as we get back the data (no waiting until all is done) return response.writeAndFlush(new ServerSentEvent(SimpleJson.mapToJson(data))); }); }

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public Observable handle(HttpServerRequest request, HttpServerResponse response) { // first request User object return getUser(request.getQueryParameters().get("userId")).flatMap(user -> { // then fetch personal catalog Observable> catalog = getPersonalizedCatalog(user) .flatMap(catalogList -> { return catalogList.videos().> flatMap(video -> { Observable bookmark = getBookmark(video); Observable rating = getRating(video); Observable metadata = getMetadata(video); return Observable.zip(bookmark, rating, metadata, (b, r, m) -> { return combineVideoData(video, b, r, m); }); }); }); // and fetch social data in parallel Observable> social = getSocialData(user).map(s -> { return s.getDataAsMap(); }); // merge the results return Observable.merge(catalog, social); }).flatMap(data -> { // output as SSE as we get back the data (no waiting until all is done) return response.writeAndFlush(new ServerSentEvent(SimpleJson.mapToJson(data))); }); }

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       Observable.zip(a,  b,  (a,  b)  -­‐>  {                ...  operate  on  values  from  both  a  &  b  ...              return  Arrays.asList(a,  b);          }) zip { ( , ) }

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public Observable handle(HttpServerRequest request, HttpServerResponse response) { // first request User object return getUser(request.getQueryParameters().get("userId")).flatMap(user -> { // then fetch personal catalog Observable> catalog = getPersonalizedCatalog(user) .flatMap(catalogList -> { return catalogList.videos().> flatMap(video -> { Observable bookmark = getBookmark(video); Observable rating = getRating(video); Observable metadata = getMetadata(video); return Observable.zip(bookmark, rating, metadata, (b, r, m) -> { return combineVideoData(video, b, r, m); }); }); }); // and fetch social data in parallel Observable> social = getSocialData(user).map(s -> { return s.getDataAsMap(); }); // merge the results return Observable.merge(catalog, social); }).flatMap(data -> { // output as SSE as we get back the data (no waiting until all is done) return response.writeAndFlush(new ServerSentEvent(SimpleJson.mapToJson(data))); }); }

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public Observable handle(HttpServerRequest request, HttpServerResponse response) { // first request User object return getUser(request.getQueryParameters().get("userId")).flatMap(user -> { // then fetch personal catalog Observable> catalog = getPersonalizedCatalog(user) .flatMap(catalogList -> { return catalogList.videos().> flatMap(video -> { Observable bookmark = getBookmark(video); Observable rating = getRating(video); Observable metadata = getMetadata(video); return Observable.zip(bookmark, rating, metadata, (b, r, m) -> { return combineVideoData(video, b, r, m); }); }); }); // and fetch social data in parallel Observable> social = getSocialData(user).map(s -> { return s.getDataAsMap(); }); // merge the results return Observable.merge(catalog, social); }).flatMap(data -> { // output as SSE as we get back the data (no waiting until all is done) return response.writeAndFlush(new ServerSentEvent(SimpleJson.mapToJson(data))); }); }

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public Observable handle(HttpServerRequest request, HttpServerResponse response) { // first request User object return getUser(request.getQueryParameters().get("userId")).flatMap(user -> { // then fetch personal catalog Observable> catalog = getPersonalizedCatalog(user) .flatMap(catalogList -> { return catalogList.videos().> flatMap(video -> { Observable bookmark = getBookmark(video); Observable rating = getRating(video); Observable metadata = getMetadata(video); return Observable.zip(bookmark, rating, metadata, (b, r, m) -> { return combineVideoData(video, b, r, m); }); }); }); // and fetch social data in parallel Observable> social = getSocialData(user).map(s -> { return s.getDataAsMap(); }); // merge the results return Observable.merge(catalog, social); }).flatMap(data -> { // output as SSE as we get back the data (no waiting until all is done) return response.writeAndFlush(new ServerSentEvent(SimpleJson.mapToJson(data))); }); }

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public Observable handle(HttpServerRequest request, HttpServerResponse response) { // first request User object return getUser(request.getQueryParameters().get("userId")).flatMap(user -> { // then fetch personal catalog Observable> catalog = getPersonalizedCatalog(user) .flatMap(catalogList -> { return catalogList.videos().> flatMap(video -> { Observable bookmark = getBookmark(video); Observable rating = getRating(video); Observable metadata = getMetadata(video); return Observable.zip(bookmark, rating, metadata, (b, r, m) -> { return combineVideoData(video, b, r, m); }); }); }); // and fetch social data in parallel Observable> social = getSocialData(user).map(s -> { return s.getDataAsMap(); }); // merge the results return Observable.merge(catalog, social); }).flatMap(data -> { // output as SSE as we get back the data (no waiting until all is done) return response.writeAndFlush(new ServerSentEvent(SimpleJson.mapToJson(data))); }); }

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class  VideoService  {        def  VideoList  getPersonalizedListOfMovies(userId);        def  VideoBookmark  getBookmark(userId,  videoId);        def  VideoRating  getRating(userId,  videoId);        def  VideoMetadata  getMetadata(videoId);   } class  VideoService  {        def  Observable  getPersonalizedListOfMovies(userId);        def  Observable  getBookmark(userId,  videoId);        def  Observable  getRating(userId,  videoId);        def  Observable  getMetadata(videoId);   } ... with an observable api: replaced the blocking api ...

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Async Facade Blocking Code Servlet Sync/Async Bridge Challenges Mixing Approaches

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Async Facade Blocking Code Servlet Sync/Async Bridge too many threads

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Async Facade Blocking Code Servlet Sync/Async Bridge hard to tune & shed load

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Async Facade Blocking Code Servlet Sync/Async Bridge easy to block async code

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getOrdersAsync(1) .flatMap(o -> { return getProductsAsync(o) .flatMap(p -> { return getShippingStatusAsync(o, p); }); }); getOrdersAsync(1) .flatMap(o -> { return getProductsAsync(o) .map(p -> { return getShippingStatus(o, p); }); }); concurrent → synchronous →

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getOrdersAsync(1) .flatMap(o -> { return getProductsAsync(o) .flatMap(p -> { return getShippingStatusAsync(o, p); }); }); getOrdersAsync(1) .flatMap(o -> { return getProductsAsync(o) .map(p -> { return getShippingStatus(o, p); }); }); concurrent → synchronous →

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getOrdersAsync(1) .flatMap(o -> { return getProductsAsync(o) .flatMap(p -> { return getShippingStatusAsync(o, p); }); }); getOrdersAsync(1) .flatMap(o -> { return getProductsAsync(o) .map(p -> { return getShippingStatus(o, p); }); }); Async Facade only has Observable APIs

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So what about going “fully reactive”?

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“cause it’s better”

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“cause it’s better” :-/

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“it’s worse”

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“it doesn’t matter”

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green threads, native threads, fibers, actors, event loops, theoretically equivalent, OS kernels, etc, etc, etc …

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C10k and beyond

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What to bet future on?

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What to bet future on?

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WSPerfLab: https://github.com/Netflix-Skunkworks/WSPerfLab

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WSPerfLab: https://github.com/Netflix-Skunkworks/WSPerfLab

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WSPerfLab: https://github.com/Netflix-Skunkworks/WSPerfLab

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WSPerfLab: https://github.com/Netflix-Skunkworks/WSPerfLab

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WSPerfLab: https://github.com/Netflix-Skunkworks/WSPerfLab

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WSPerfLab: https://github.com/Netflix-Skunkworks/WSPerfLab 154ms

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Intel(R) Core(TM) i5-2400 CPU @ 3.10GHz: 4 cores, 1 thread per core OpenJDK 8 with frame pointer patch RxNetty 0.4.8 with Netty 4.0.25.Final vs Tomcat 7.0.45

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0% 25% 50% 75% 100% 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 100010501100 RxNetty Tomcat CPU Usage in Percent concurrent clients Testing drove both tests near 100% cpu usage

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0ms 0.225ms 0.45ms 0.675ms 0.9ms 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 100010501100 RxNetty Tomcat CPU Consumption per Request concurrent clients • Netty has lower CPU consumption per request • Netty keeps getting faster under load, Tomcat gets slower

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0rps 1250rps 2500rps 3750rps 5000rps 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 100010501100 RxNetty Tomcat Throughput concurrent clients • Netty achieves higher throughput • Mostly due to lower CPU consumption per request

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0ms 70ms 140ms 210ms 280ms 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 100010501100 RxNetty Tomcat Average Latency concurrent clients Theoretical best possible for test case is 154ms

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0ms 750ms 1500ms 2250ms 3000ms 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 100010501100 RxNetty Tomcat Max Latency concurrent clients Tomcat latency degradation is far more severe than Netty

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0ipc 0.175ipc 0.35ipc 0.525ipc 0.7ipc 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 100010501100 RxNetty Tomcat CPU Instructions per Cycle concurrent clients Netty increases instructions per cycle as load increases

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0 400000 800000 1200000 1600000 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 100010501100 RxNetty Tomcat Thread Migrations concurrent clients significant divergence

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0 400000 800000 1200000 1600000 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 100010501100 RxNetty Tomcat Thread Migrations concurrent clients Under light load both are similar

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0 400000 800000 1200000 1600000 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 100010501100 RxNetty Tomcat Thread Migrations concurrent clients Increased load causes less migrations, improving IPC and CPU usage per request with event loop architecture

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Why? • More efficient framework code • object allocation rates and GC costs • Event loop architecture • reduced thread migrations • cache warmth → memory locality → instructions per cycle → lower cpu consumption per request • Thread pool architecture • lock contention • thread migrations

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Why? • More efficient framework code • object allocation rates and GC costs • Event loop architecture • reduced thread migrations • cache warmth → memory locality → instructions per cycle → lower cpu consumption per request • Thread pool architecture • lock contention • thread migrations

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Why? • More efficient framework code • object allocation rates and GC costs • Event loop architecture • reduced thread migrations • cache warmth → memory locality → instructions per cycle → lower cpu consumption per request • Thread pool architecture • lock contention • thread migrations

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Why? • More efficient framework code • object allocation rates and GC costs • Event loop architecture • reduced thread migrations • cache warmth → memory locality → instructions per cycle → lower cpu consumption per request • Thread pool architecture • lock contention • thread migrations • Many more details …

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With current JVM and Linux, event loops have efficiency benefits.

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Simpler But Not Easier

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0ms 750ms 1500ms 2250ms 3000ms 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 100010501100 RxNetty Tomcat Simpler But Not Easier

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A fully async architecture does have benefits.

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Reactive programming can be incrementally applied.

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Mixed Codebases

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Concurrency via Async Service Composition

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Leverage RxJava Schedulers and Threads

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Leverage RxJava Schedulers and Threads (or use Hystrix)

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Concurrency is still non-trivial

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Rx doesn’t trivialize it Concurrency is still non-trivial

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Reactive Programming in the Netflix API with RxJava http://techblog.netflix.com/2013/02/rxjava-netflix-api.html Optimizing the Netflix API http://techblog.netflix.com/2013/01/optimizing-netflix-api.html Reactive Extensions (Rx) http://www.reactivex.io Reactive Streams https://github.com/reactive-streams/reactive-streams Ben Christensen @benjchristensen RxJava https://github.com/ReactiveX/RxJava @RxJava RxJS http://reactive-extensions.github.io/RxJS/ @ReactiveX jobs.netflix.com Dragon Image: http://www.clipartpanda.com/clipart_images/you-can-use-this-clip-art-on-2194929 Greenfield Image: https://kvaes.wordpress.com/2013/06/05/lingo-explained-greenfield-vs-brownfield/ NY City Image: https://thesandincalifornia.files.wordpress.com/2012/05/newyorkcity-madness.jpg Futuristic City: http://i.imgur.com/rPTkr9D.jpg