Initial implementation of AsyncSubject

rxjava-core/src/main/java/rx/subjects/AsyncSubject.java

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+/**
+ * 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.subjects;
+
+import static org.mockito.Matchers.any;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Matchers.anyString;
+
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicReference;
+
+import org.junit.Test;
+import org.mockito.Mockito;
+
+import rx.Observer;
+import rx.Subscription;
+import rx.util.AtomicObservableSubscription;
+import rx.util.SynchronizedObserver;
+import rx.util.functions.Action1;
+import rx.util.functions.Func0;
+import rx.util.functions.Func1;
+
+/**
+ * Subject that publishes only the last event to each {@link Observer} that has subscribed when the completes. 
+ * <p>
+ * Example usage:
+ * <p>
+ * <pre> {@code
+
+  // observer will receive no onNext events.
+  AsyncSubject<Object> subject = AsyncSubject.create();
+  subject.subscribe(observer);
+  subject.onNext("one");
+  subject.onNext("two");
+  subject.onNext("three");
+
+  // observer will receive "three" as the only onNext event.
+  AsyncSubject<Object> subject = AsyncSubject.create();
+  subject.subscribe(observer);
+  subject.onNext("one");
+  subject.onNext("two");
+  subject.onNext("three");
+  subject.onCompleted();
+
+  } </pre>
+ * 
+ * @param <T>
+ */
+public class AsyncSubject<T> extends Subject<T, T> {
+
+    public static <T> AsyncSubject<T> create() {
+        final ConcurrentHashMap<Subscription, Observer<T>> observers = new ConcurrentHashMap<Subscription, Observer<T>>();
+
+        Func1<Observer<T>, Subscription> onSubscribe = new Func1<Observer<T>, Subscription>() {
+            @Override
+            public Subscription call(Observer<T> observer) {
+                final AtomicObservableSubscription subscription = new AtomicObservableSubscription();
+
+                subscription.wrap(new Subscription() {
+                    @Override
+                    public void unsubscribe() {
+                        // on unsubscribe remove it from the map of outbound observers to notify
+                        observers.remove(subscription);
+                    }
+                });
+
+                // on subscribe add it to the map of outbound observers to notify
+                observers.put(subscription, new SynchronizedObserver<T>(observer, subscription));
+                return subscription;
+            }
+        };
+
+        return new AsyncSubject<T>(onSubscribe, observers);
+    }
+
+    private final ConcurrentHashMap<Subscription, Observer<T>> observers;
+    private final AtomicReference<T> currentValue;
+
+    protected AsyncSubject(Func1<Observer<T>, Subscription> onSubscribe, ConcurrentHashMap<Subscription, Observer<T>> observers) {
+        super(onSubscribe);
+        this.observers = observers;
+        this.currentValue = new AtomicReference<T>();
+    }
+
+    @Override
+    public void onCompleted() {
+    	T finalValue = currentValue.get();
+    	for (Observer<T> observer : observers.values()) {
+			observer.onNext(finalValue);
+    	}
+        for (Observer<T> observer : observers.values()) {
+            observer.onCompleted();
+        }
+    }
+
+    @Override
+    public void onError(Exception e) {
+        for (Observer<T> observer : observers.values()) {
+            observer.onError(e);
+        }
+    }
+
+    @Override
+    public void onNext(T args) {
+        currentValue.set(args);
+    }
+
+    public static class UnitTest {
+
+        private final Exception testException = new Exception();
+
+        @Test
+        public void testNeverCompleted() {
+        	AsyncSubject<Object> subject = AsyncSubject.create();
+
+            @SuppressWarnings("unchecked")
+            Observer<String> aObserver = mock(Observer.class);
+            subject.subscribe(aObserver);
+
+            subject.onNext("one");
+            subject.onNext("two");
+            subject.onNext("three");
+
+            assertNeverCompletedObserver(aObserver);
+        }
+
+        private void assertNeverCompletedObserver(Observer<String> aObserver)
+        {
+            verify(aObserver, Mockito.never()).onNext(anyString());
+            verify(aObserver, Mockito.never()).onError(testException);
+            verify(aObserver, Mockito.never()).onCompleted();
+        }
+
+        @Test
+        public void testCompleted() {
+        	AsyncSubject<Object> subject = AsyncSubject.create();
+
+            @SuppressWarnings("unchecked")
+            Observer<String> aObserver = mock(Observer.class);
+            subject.subscribe(aObserver);
+
+            subject.onNext("one");
+            subject.onNext("two");
+            subject.onNext("three");
+            subject.onCompleted();
+
+            assertCompletedObserver(aObserver);
+        }
+
+        private void assertCompletedObserver(Observer<String> aObserver)
+        {
+            verify(aObserver, times(1)).onNext("three");
+            verify(aObserver, Mockito.never()).onError(any(Exception.class));
+            verify(aObserver, times(1)).onCompleted();
+        }
+
+        @Test
+        public void testError() {
+        	AsyncSubject<Object> subject = AsyncSubject.create();
+
+            @SuppressWarnings("unchecked")
+            Observer<String> aObserver = mock(Observer.class);
+            subject.subscribe(aObserver);
+
+            subject.onNext("one");
+            subject.onNext("two");
+            subject.onNext("three");
+            subject.onError(testException);
+            subject.onNext("four");
+            subject.onError(new Exception());
+            subject.onCompleted();
+
+            assertErrorObserver(aObserver);
+        }
+
+        private void assertErrorObserver(Observer<String> aObserver)
+        {
+            verify(aObserver, Mockito.never()).onNext(anyString());
+            verify(aObserver, times(1)).onError(testException);
+            verify(aObserver, Mockito.never()).onCompleted();
+        }
+
+        @Test
+        public void testUnsubscribeBeforeCompleted() {
+        	AsyncSubject<Object> subject = AsyncSubject.create();
+
+            @SuppressWarnings("unchecked")
+            Observer<String> aObserver = mock(Observer.class);
+            Subscription subscription = subject.subscribe(aObserver);
+
+            subject.onNext("one");
+            subject.onNext("two");
+
+            subscription.unsubscribe();
+            assertNoOnNextEventsReceived(aObserver);
+
+            subject.onNext("three");
+            subject.onCompleted();
+
+            assertNoOnNextEventsReceived(aObserver);
+        }
+
+        private void assertNoOnNextEventsReceived(Observer<String> aObserver)
+        {
+            verify(aObserver, Mockito.never()).onNext(anyString());
+            verify(aObserver, Mockito.never()).onError(any(Exception.class));
+            verify(aObserver, Mockito.never()).onCompleted();
+        }
+
+        @Test
+        public void testUnsubscribe()
+        {
+            UnsubscribeTester.test(new Func0<AsyncSubject<Object>>()
+            {
+                @Override
+                public AsyncSubject<Object> call()
+                {
+                    return AsyncSubject.create();
+                }
+            }, new Action1<AsyncSubject<Object>>()
+            {
+                @Override
+                public void call(AsyncSubject<Object> DefaultSubject)
+                {
+                    DefaultSubject.onCompleted();
+                }
+            }, new Action1<AsyncSubject<Object>>()
+            {
+                @Override
+                public void call(AsyncSubject<Object> DefaultSubject)
+                {
+                    DefaultSubject.onError(new Exception());
+                }
+            }, 
+            null);
+        }
+    }
+}