Operator: throttleFirst

rxjava-core/src/main/java/rx/Observable.java

@@ -64,6 +64,7 @@
 import rx.operators.OperationTakeLast;
 import rx.operators.OperationTakeUntil;
 import rx.operators.OperationTakeWhile;
+import rx.operators.OperationThrottleFirst;
 import rx.operators.OperationTimestamp;
 import rx.operators.OperationToObservableFuture;
 import rx.operators.OperationToObservableIterable;
@@ -1809,6 +1810,34 @@ public static Observable<Long> interval(long interval, TimeUnit unit, Scheduler
         return create(OperationInterval.interval(interval, unit, scheduler));
     }
 
+    /**
+     * Throttles to first value in each window.
+     * 
+     * @param windowDuration
+     *            Duration of windows within with the first value will be chosen.
+     * @param unit
+     *            The unit of time for the specified timeout.
+     * @return Observable which performs the throttle operation.
+     */
+    public Observable<T> throttleFirst(long windowDuration, TimeUnit unit) {
+        return create(OperationThrottleFirst.throttleFirst(this, windowDuration, unit));
+    }
+
+    /**
+     * Throttles to first value in each window.
+     * 
+     * @param windowDuration
+     *            Duration of windows within with the first value will be chosen.
+     * @param unit
+     *            The unit of time for the specified timeout.
+     * @param scheduler
+     *            The {@link Scheduler} to use internally to manage the timers which handle timeout for each event.
+     * @return Observable which performs the throttle operation.
+     */
+    public Observable<T> throttleFirst(long windowDuration, TimeUnit unit, Scheduler scheduler) {
+        return create(OperationThrottleFirst.throttleFirst(this, windowDuration, unit, scheduler));
+    }
+
     /**
      * Wraps each item emitted by a source Observable in a {@link Timestamped} object.
      * <p>

rxjava-core/src/main/java/rx/concurrency/TestScheduler.java

@@ -19,20 +19,22 @@
 import java.util.PriorityQueue;
 import java.util.Queue;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
 
 import rx.Scheduler;
 import rx.Subscription;
-import rx.subscriptions.Subscriptions;
 import rx.util.functions.Func2;
 
 public class TestScheduler extends Scheduler {
     private final Queue<TimedAction<?>> queue = new PriorityQueue<TimedAction<?>>(11, new CompareActionsByTime());
 
     private static class TimedAction<T> {
+
         private final long time;
         private final Func2<? super Scheduler, ? super T, ? extends Subscription> action;
         private final T state;
         private final TestScheduler scheduler;
+        private final AtomicBoolean isCancelled = new AtomicBoolean(false);
 
         private TimedAction(TestScheduler scheduler, long time, Func2<? super Scheduler, ? super T, ? extends Subscription> action, T state) {
             this.time = time;
@@ -41,6 +43,10 @@ private TimedAction(TestScheduler scheduler, long time, Func2<? super Scheduler,
             this.scheduler = scheduler;
         }
 
+        public void cancel() {
+            isCancelled.set(true);
+        }
+
         @Override
         public String toString() {
             return String.format("TimedAction(time = %d, action = %s)", time, action.toString());
@@ -84,8 +90,12 @@ private void triggerActions(long targetTimeInNanos) {
             }
             time = current.time;
             queue.remove();
-            // because the queue can have wildcards we have to ignore the type T for the state
-            ((Func2<Scheduler, Object, Subscription>) current.action).call(current.scheduler, current.state);
+
+            // Only execute if the TimedAction has not yet been cancelled
+            if (!current.isCancelled.get()) {
+                // because the queue can have wildcards we have to ignore the type T for the state
+                ((Func2<Scheduler, Object, Subscription>) current.action).call(current.scheduler, current.state);
+            }
         }
         time = targetTimeInNanos;
     }
@@ -97,7 +107,14 @@ public <T> Subscription schedule(T state, Func2<? super Scheduler, ? super T, ?
 
     @Override
     public <T> Subscription schedule(T state, Func2<? super Scheduler, ? super T, ? extends Subscription> action, long delayTime, TimeUnit unit) {
-        queue.add(new TimedAction<T>(this, time + unit.toNanos(delayTime), action, state));
-        return Subscriptions.empty();
+        final TimedAction<T> timedAction = new TimedAction<T>(this, time + unit.toNanos(delayTime), action, state);
+        queue.add(timedAction);
+
+        return new Subscription() {
+            @Override
+            public void unsubscribe() {
+                timedAction.cancel();
+            }
+        };
     }
 }

rxjava-core/src/main/java/rx/operators/OperationThrottleFirst.java

@@ -0,0 +1,185 @@
+/**
+ * Copyright 2013 Netflix, Inc.
+ * 
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package rx.operators;
+
+import static org.mockito.Matchers.*;
+import static org.mockito.Mockito.*;
+
+import java.util.concurrent.TimeUnit;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.mockito.InOrder;
+
+import rx.Observable;
+import rx.Observable.OnSubscribeFunc;
+import rx.Observer;
+import rx.Scheduler;
+import rx.Subscription;
+import rx.concurrency.Schedulers;
+import rx.concurrency.TestScheduler;
+import rx.subscriptions.Subscriptions;
+import rx.util.functions.Action0;
+import rx.util.functions.Func1;
+
+/**
+ * Throttle by windowing a stream and returning the first value in each window.
+ */
+public final class OperationThrottleFirst {
+
+    /**
+     * Throttles to first value in each window.
+     * 
+     * @param items
+     *            The {@link Observable} which is publishing events.
+     * @param windowDuration
+     *            Duration of windows within with the first value will be chosen.
+     * @param unit
+     *            The unit of time for the specified timeout.
+     * @return A {@link Func1} which performs the throttle operation.
+     */
+    public static <T> OnSubscribeFunc<T> throttleFirst(Observable<T> items, long windowDuration, TimeUnit unit) {
+        return throttleFirst(items, windowDuration, unit, Schedulers.threadPoolForComputation());
+    }
+
+    /**
+     * Throttles to first value in each window.
+     * 
+     * @param items
+     *            The {@link Observable} which is publishing events.
+     * @param windowDuration
+     *            Duration of windows within with the first value will be chosen.
+     * @param unit
+     *            The unit of time for the specified timeout.
+     * @param scheduler
+     *            The {@link Scheduler} to use internally to manage the timers which handle timeout for each event.
+     * @return A {@link Func1} which performs the throttle operation.
+     */
+    public static <T> OnSubscribeFunc<T> throttleFirst(final Observable<T> items, final long windowDuration, final TimeUnit unit, final Scheduler scheduler) {
+        return new OnSubscribeFunc<T>() {
+            @Override
+            public Subscription onSubscribe(Observer<? super T> observer) {
+                return items.window(windowDuration, unit, scheduler).flatMap(new Func1<Observable<T>, Observable<T>>() {
+
+                    @Override
+                    public Observable<T> call(Observable<T> o) {
+                        return o.takeFirst();
+                    }
+                }).subscribe(observer);
+            }
+        };
+    }
+
+    public static class UnitTest {
+
+        private TestScheduler scheduler;
+        private Observer<String> observer;
+
+        @Before
+        @SuppressWarnings("unchecked")
+        public void before() {
+            scheduler = new TestScheduler();
+            observer = mock(Observer.class);
+        }
+
+        @Test
+        public void testThrottlingWithCompleted() {
+            Observable<String> source = Observable.create(new OnSubscribeFunc<String>() {
+                @Override
+                public Subscription onSubscribe(Observer<? super String> observer) {
+                    publishNext(observer, 100, "one");    // publish as it's first
+                    publishNext(observer, 300, "two");    // skip as it's last within the first 400
+                    publishNext(observer, 900, "three");   // publish
+                    publishNext(observer, 905, "four");   // skip
+                    publishCompleted(observer, 1000);     // Should be published as soon as the timeout expires.
+
+                    return Subscriptions.empty();
+                }
+            });
+
+            Observable<String> sampled = Observable.create(OperationThrottleFirst.throttleFirst(source, 400, TimeUnit.MILLISECONDS, scheduler));
+            sampled.subscribe(observer);
+
+            InOrder inOrder = inOrder(observer);
+
+            scheduler.advanceTimeTo(1000, TimeUnit.MILLISECONDS);
+            inOrder.verify(observer, times(1)).onNext("one");
+            inOrder.verify(observer, times(0)).onNext("two");
+            inOrder.verify(observer, times(1)).onNext("three");
+            inOrder.verify(observer, times(0)).onNext("four");
+            inOrder.verify(observer, times(1)).onCompleted();
+            inOrder.verifyNoMoreInteractions();
+        }
+
+        @Test
+        public void testThrottlingWithError() {
+            Observable<String> source = Observable.create(new OnSubscribeFunc<String>() {
+                @Override
+                public Subscription onSubscribe(Observer<? super String> observer) {
+                    Exception error = new TestException();
+                    publishNext(observer, 100, "one");    // Should be published since it is first
+                    publishNext(observer, 200, "two");    // Should be skipped since onError will arrive before the timeout expires
+                    publishError(observer, 300, error);   // Should be published as soon as the timeout expires.
+
+                    return Subscriptions.empty();
+                }
+            });
+
+            Observable<String> sampled = Observable.create(OperationThrottleFirst.throttleFirst(source, 400, TimeUnit.MILLISECONDS, scheduler));
+            sampled.subscribe(observer);
+
+            InOrder inOrder = inOrder(observer);
+
+            scheduler.advanceTimeTo(400, TimeUnit.MILLISECONDS);
+            inOrder.verify(observer).onNext("one");
+            inOrder.verify(observer).onError(any(TestException.class));
+            inOrder.verifyNoMoreInteractions();
+        }
+
+        private <T> void publishCompleted(final Observer<T> observer, long delay) {
+            scheduler.schedule(new Action0() {
+                @Override
+                public void call() {
+                    observer.onCompleted();
+                }
+            }, delay, TimeUnit.MILLISECONDS);
+        }
+
+        private <T> void publishError(final Observer<T> observer, long delay, final Exception error) {
+            scheduler.schedule(new Action0() {
+                @Override
+                public void call() {
+                    observer.onError(error);
+                }
+            }, delay, TimeUnit.MILLISECONDS);
+        }
+
+        private <T> void publishNext(final Observer<T> observer, long delay, final T value) {
+            scheduler.schedule(new Action0() {
+                @Override
+                public void call() {
+                    observer.onNext(value);
+                }
+            }, delay, TimeUnit.MILLISECONDS);
+        }
+
+        @SuppressWarnings("serial")
+        private class TestException extends Exception {
+        }
+
+    }
+
+}

rxjava-core/src/test/java/rx/ThrottleFirstTests.java

@@ -0,0 +1,46 @@
+package rx;
+
+import static org.mockito.Mockito.*;
+
+import java.util.concurrent.TimeUnit;
+
+import org.junit.Test;
+import org.mockito.InOrder;
+
+import rx.concurrency.TestScheduler;
+import rx.subjects.PublishSubject;
+
+public class ThrottleFirstTests {
+
+    @Test
+    public void testThrottle() {
+        @SuppressWarnings("unchecked")
+        Observer<Integer> observer = mock(Observer.class);
+        TestScheduler s = new TestScheduler();
+        PublishSubject<Integer> o = PublishSubject.create();
+        o.throttleFirst(500, TimeUnit.MILLISECONDS, s).subscribe(observer);
+
+        // send events with simulated time increments
+        s.advanceTimeTo(0, TimeUnit.MILLISECONDS);
+        o.onNext(1); // deliver
+        o.onNext(2); // skip
+        s.advanceTimeTo(501, TimeUnit.MILLISECONDS);
+        o.onNext(3); // deliver
+        s.advanceTimeTo(600, TimeUnit.MILLISECONDS);
+        o.onNext(4); // skip
+        s.advanceTimeTo(700, TimeUnit.MILLISECONDS);
+        o.onNext(5); // skip
+        o.onNext(6); // skip
+        s.advanceTimeTo(1001, TimeUnit.MILLISECONDS);
+        o.onNext(7); // deliver
+        s.advanceTimeTo(1501, TimeUnit.MILLISECONDS);
+        o.onCompleted();
+
+        InOrder inOrder = inOrder(observer);
+        inOrder.verify(observer).onNext(1);
+        inOrder.verify(observer).onNext(3);
+        inOrder.verify(observer).onNext(7);
+        inOrder.verify(observer).onCompleted();
+        inOrder.verifyNoMoreInteractions();
+    }
+}