Observable.from(iterable) should emit onCompleted even if none requested when iterable is empty

Author: davidmoten

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

@@ -44,7 +44,10 @@ public OnSubscribeFromIterable(Iterable<? extends T> iterable) {
     @Override
     public void call(final Subscriber<? super T> o) {
         final Iterator<? extends T> it = is.iterator();
-        o.setProducer(new IterableProducer<T>(o, it));
+        if (!it.hasNext() && !o.isUnsubscribed())
+            o.onCompleted();
+        else 
+            o.setProducer(new IterableProducer<T>(o, it));
     }
 
     private static final class IterableProducer<T> implements Producer {
@@ -62,12 +65,11 @@ private IterableProducer(Subscriber<? super T> o, Iterator<? extends T> it) {
 
         @Override
         public void request(long n) {
-            if (REQUESTED_UPDATER.get(this) == Long.MAX_VALUE) {
+            if (requested == Long.MAX_VALUE) {
                 // already started with fast-path
                 return;
             }
-            if (n == Long.MAX_VALUE) {
-                REQUESTED_UPDATER.set(this, n);
+            if (n == Long.MAX_VALUE && REQUESTED_UPDATER.compareAndSet(this, 0, Long.MAX_VALUE)) {
                 // fast-path without backpressure
                 while (it.hasNext()) {
                     if (o.isUnsubscribed()) {
@@ -78,7 +80,7 @@ public void request(long n) {
                 if (!o.isUnsubscribed()) {
                     o.onCompleted();
                 }
-            } else if(n > 0) {
+            } else if (n > 0) {
                 // backpressure is requested
                 long _c = BackpressureUtils.getAndAddRequest(REQUESTED_UPDATER, this, n);
                 if (_c == 0) {

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

@@ -27,6 +27,7 @@
 import java.util.Iterator;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
 
 import org.junit.Test;
 import org.mockito.Mockito;
@@ -74,12 +75,12 @@ public Iterator<String> iterator() {
 
                     @Override
                     public boolean hasNext() {
-                        return i++ < 3;
+                        return i < 3;
                     }
 
                     @Override
                     public String next() {
-                        return String.valueOf(i);
+                        return String.valueOf(++i);
                     }
 
                     @Override
@@ -193,5 +194,31 @@ public void onNext(Integer t) {
         assertTrue(latch.await(10, TimeUnit.SECONDS));
     }
 
+    @Test
+    public void testFromEmptyIterableWhenZeroRequestedShouldStillEmitOnCompletedEagerly() {
+        final AtomicBoolean completed = new AtomicBoolean(false);
+        Observable.from(Collections.emptyList()).subscribe(new Subscriber<Object>() {
+
+            @Override
+            public void onStart() {
+                request(0);
+            }
+            
+            @Override
+            public void onCompleted() {
+                completed.set(true);
+            }
 
+            @Override
+            public void onError(Throwable e) {
+                
+            }
+
+            @Override
+            public void onNext(Object t) {
+                
+            }});
+        assertTrue(completed.get());
+    }
+    
 }