improve perf of OperatorIgnoreElements

Author: davidmoten

src/main/java/rx/Observable.java

@@ -4941,7 +4941,7 @@ public final <T2, D1, D2, R> Observable<R> groupJoin(Observable<T2> right, Func1
      * @see <a href="http://reactivex.io/documentation/operators/ignoreelements.html">ReactiveX operators documentation: IgnoreElements</a>
      */
     public final Observable<T> ignoreElements() {
-        return filter(UtilityFunctions.alwaysFalse());
+        return lift(OperatorIgnoreElements.<T> instance());
     }
 
     /**

src/main/java/rx/internal/operators/OperatorIgnoreElements.java

@@ -0,0 +1,58 @@
+/**
+ * Copyright 2014 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.internal.operators;
+
+import rx.Observable.Operator;
+import rx.Subscriber;
+
+public class OperatorIgnoreElements<T> implements Operator<T, T> {
+
+    private static class Holder {
+        static final OperatorIgnoreElements<?> INSTANCE = new OperatorIgnoreElements<Object>();
+    }
+    
+    @SuppressWarnings("unchecked")
+    public static <T> OperatorIgnoreElements<T> instance() {
+        return (OperatorIgnoreElements<T>) Holder.INSTANCE;
+    }
+
+    private OperatorIgnoreElements() {
+
+    }
+
+    @Override
+    public Subscriber<? super T> call(final Subscriber<? super T> child) {
+        return new Subscriber<T>(child) {
+
+            @Override
+            public void onCompleted() {
+                child.onCompleted();
+            }
+
+            @Override
+            public void onError(Throwable e) {
+                child.onError(e);
+            }
+
+            @Override
+            public void onNext(T t) {
+                // ignore element
+            }
+
+        };
+    }
+
+}

src/test/java/rx/internal/operators/OperatorIgnoreElementsTest.java

@@ -0,0 +1,80 @@
+package rx.internal.operators;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import java.util.Arrays;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import org.junit.Test;
+
+import rx.Observable;
+import rx.functions.Action0;
+import rx.functions.Action1;
+import rx.observers.TestSubscriber;
+
+public class OperatorIgnoreElementsTest {
+
+    @Test
+    public void testWithEmpty() {
+        assertTrue(Observable.empty().ignoreElements().isEmpty().toBlocking().single());
+    }
+
+    @Test
+    public void testWithNonEmpty() {
+        assertTrue(Observable.just(1, 2, 3).ignoreElements().isEmpty().toBlocking().single());
+    }
+
+    @Test
+    public void testUpstreamIsProcessedButIgnored() {
+        final int num = 10;
+        final AtomicInteger upstreamCount = new AtomicInteger();
+        int count = Observable.range(1, num)
+                .doOnNext(new Action1<Integer>() {
+                    @Override
+                    public void call(Integer t) {
+                        upstreamCount.incrementAndGet();
+                    }
+                })
+                .ignoreElements()
+                .count().toBlocking().single();
+        assertEquals(num, upstreamCount.get());
+        assertEquals(0, count);
+    }
+    
+    @Test
+    public void testCompletedOk() {
+        TestSubscriber<Object> ts = new TestSubscriber<Object>();
+        Observable.range(1, 10).ignoreElements().subscribe(ts);
+        ts.assertNoErrors();
+        ts.assertReceivedOnNext(Arrays.asList());
+        ts.assertTerminalEvent();
+        ts.assertUnsubscribed();
+    }
+    
+    @Test
+    public void testErrorReceived() {
+        TestSubscriber<Object> ts = new TestSubscriber<Object>();
+        RuntimeException ex = new RuntimeException("boo");
+        Observable.error(ex).ignoreElements().subscribe(ts);
+        ts.assertReceivedOnNext(Arrays.asList());
+        ts.assertTerminalEvent();
+        ts.assertUnsubscribed();
+        assertEquals(1, ts.getOnErrorEvents().size());
+        assertEquals("boo", ts.getOnErrorEvents().get(0).getMessage());
+    }
+    
+    @Test
+    public void testUnsubscribesFromUpstream() {
+        final AtomicBoolean unsub = new AtomicBoolean();
+        Observable.range(1, 10).doOnUnsubscribe(new Action0() {
+            @Override
+            public void call() {
+                unsub.set(true);
+            }})
+            .subscribe();
+        assertTrue(unsub.get());
+    }
+
+}

src/test/java/rx/internal/operators/OperatorTakeLastOneTest.java

@@ -14,7 +14,6 @@
 
 import rx.Observable;
 import rx.Subscriber;
-import rx.Subscription;
 import rx.functions.Action0;
 import rx.functions.Action1;
 import rx.observers.TestSubscriber;