Merge pull request ReactiveX#1552 from abersnaze/most-recent-null

Fixing a bug and a potential for other concurrency issues.

Author: benjchristensen

rxjava-core/src/main/java/rx/internal/operators/BlockingOperatorMostRecent.java

@@ -16,6 +16,7 @@
 package rx.internal.operators;
 
 import java.util.Iterator;
+import java.util.NoSuchElementException;
 
 import rx.Observable;
 import rx.Subscriber;
@@ -41,54 +42,24 @@ public final class BlockingOperatorMostRecent {
      *         {@code initialValue} if {@code source} has not yet emitted any items
      */
     public static <T> Iterable<T> mostRecent(final Observable<? extends T> source, final T initialValue) {
-
         return new Iterable<T>() {
             @Override
             public Iterator<T> iterator() {
                 MostRecentObserver<T> mostRecentObserver = new MostRecentObserver<T>(initialValue);
-                final MostRecentIterator<T> nextIterator = new MostRecentIterator<T>(mostRecentObserver);
 
                 /**
                  * Subscribe instead of unsafeSubscribe since this is the final subscribe in the chain
                  * since it is for BlockingObservable.
                  */
                 source.subscribe(mostRecentObserver);
 
-                return nextIterator;
+                return mostRecentObserver.getIterable();
             }
         };
-
-    }
-
-    private static class MostRecentIterator<T> implements Iterator<T> {
-
-        private final MostRecentObserver<T> observer;
-
-        private MostRecentIterator(MostRecentObserver<T> observer) {
-            this.observer = observer;
-        }
-
-        @Override
-        public boolean hasNext() {
-            return !observer.isCompleted();
-        }
-
-        @Override
-        public T next() {
-            if (observer.getThrowable() != null) {
-                throw Exceptions.propagate(observer.getThrowable());
-            }
-            return observer.getRecentValue();
-        }
-
-        @Override
-        public void remove() {
-            throw new UnsupportedOperationException("Read only iterator");
-        }
     }
 
     private static class MostRecentObserver<T> extends Subscriber<T> {
-        static final NotificationLite<Object> nl = NotificationLite.instance();
+        final NotificationLite<T> nl = NotificationLite.instance();
         volatile Object value;
 
         private MostRecentObserver(T value) {
@@ -110,19 +81,47 @@ public void onNext(T args) {
             value = nl.next(args);
         }
 
-        private boolean isCompleted() {
-            return nl.isCompleted(value);
-        }
-
-        private Throwable getThrowable() {
-            Object v = value;
-            return nl.isError(v) ? nl.getError(v) : null;
-        }
-
-        @SuppressWarnings("unchecked")
-        private T getRecentValue() {
-            return (T)value;
+        /**
+         * The {@link Iterator} return is not thread safe. In other words don't call {@link Iterator#hasNext()} in one
+         * thread expect {@link Iterator#next()} called from a different thread to work.
+         * @return
+         */
+        public Iterator<T> getIterable() {
+            return new Iterator<T>() {
+                /**
+                 * buffer to make sure that the state of the iterator doesn't change between calling hasNext() and next().
+                 */
+                private Object buf = null;
+
+                @Override
+                public boolean hasNext() {
+                    buf = value;
+                    return !nl.isCompleted(buf);
+                }
+
+                @Override
+                public T next() {
+                    try {
+                        // if hasNext wasn't called before calling next.
+                        if (buf == null)
+                            buf = value;
+                        if (nl.isCompleted(buf))
+                            throw new NoSuchElementException();
+                        if (nl.isError(buf)) {
+                            throw Exceptions.propagate(nl.getError(buf));
+                        }
+                        return nl.getValue(buf);
+                    }
+                    finally {
+                        buf = null;
+                    }
+                }
+
+                @Override
+                public void remove() {
+                    throw new UnsupportedOperationException("Read only iterator");
+                }
+            };
         }
-
     }
 }

rxjava-core/src/test/java/rx/internal/operators/BlockingOperatorMostRecentTest.java

@@ -34,6 +34,10 @@
 import rx.subjects.Subject;
 
 public class BlockingOperatorMostRecentTest {
+    @Test
+    public void testMostRecentNull() {
+        assertEquals(null, Observable.<Void>never().toBlocking().mostRecent(null).iterator().next());
+    }
 
     @Test
     public void testMostRecent() {