Add "Subscriptions.unsubscribed" to fix the 'isUnsubscribed' issue

src/main/java/rx/Observable.java

@@ -7305,7 +7305,7 @@ public final Subscription unsafeSubscribe(Subscriber<? super T> subscriber) {
                 // TODO why aren't we throwing the hook's return value.
                 throw r;
             }
-            return Subscriptions.empty();
+            return Subscriptions.unsubscribed();
         }
     }
 
@@ -7394,7 +7394,7 @@ public final Subscription subscribe(Subscriber<? super T> subscriber) {
                 // TODO why aren't we throwing the hook's return value.
                 throw r;
             }
-            return Subscriptions.empty();
+            return Subscriptions.unsubscribed();
         }
     }
 

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

@@ -51,7 +51,7 @@ public Subscription call(
                     } catch (Throwable t) {
                         Exceptions.throwIfFatal(t);
                         timeoutSubscriber.onError(t);
-                        return Subscriptions.empty();
+                        return Subscriptions.unsubscribed();
                     }
                     return o.unsafeSubscribe(new Subscriber<U>() {
 
@@ -72,7 +72,7 @@ public void onNext(U t) {
 
                     });
                 } else {
-                    return Subscriptions.empty();
+                    return Subscriptions.unsubscribed();
                 }
             }
         }, new TimeoutStub<T>() {
@@ -87,7 +87,7 @@ public Subscription call(
                 } catch (Throwable t) {
                     Exceptions.throwIfFatal(t);
                     timeoutSubscriber.onError(t);
-                    return Subscriptions.empty();
+                    return Subscriptions.unsubscribed();
                 }
                 return o.unsafeSubscribe(new Subscriber<V>() {
 

src/main/java/rx/internal/schedulers/NewThreadWorker.java

@@ -58,7 +58,7 @@ public Subscription schedule(final Action0 action) {
     @Override
     public Subscription schedule(final Action0 action, long delayTime, TimeUnit unit) {
         if (isUnsubscribed) {
-            return Subscriptions.empty();
+            return Subscriptions.unsubscribed();
         }
         return scheduleActual(action, delayTime, unit);
     }

src/main/java/rx/schedulers/CachedThreadScheduler.java

@@ -141,7 +141,7 @@ public Subscription schedule(Action0 action) {
         public Subscription schedule(Action0 action, long delayTime, TimeUnit unit) {
             if (innerSubscription.isUnsubscribed()) {
                 // don't schedule, we are unsubscribed
-                return Subscriptions.empty();
+                return Subscriptions.unsubscribed();
             }
 
             ScheduledAction s = threadWorker.scheduleActual(action, delayTime, unit);

src/main/java/rx/schedulers/EventLoopsScheduler.java

@@ -95,7 +95,7 @@ public Subscription schedule(Action0 action) {
         public Subscription schedule(Action0 action, long delayTime, TimeUnit unit) {
             if (innerSubscription.isUnsubscribed()) {
                 // don't schedule, we are unsubscribed
-                return Subscriptions.empty();
+                return Subscriptions.unsubscribed();
             }
 
             ScheduledAction s = poolWorker.scheduleActual(action, delayTime, unit);

src/main/java/rx/schedulers/ExecutorScheduler.java

@@ -71,7 +71,7 @@ public ExecutorSchedulerWorker(Executor executor) {
         @Override
         public Subscription schedule(Action0 action) {
             if (isUnsubscribed()) {
-                return Subscriptions.empty();
+                return Subscriptions.unsubscribed();
             }
             ExecutorAction ea = new ExecutorAction(action, tasks);
             tasks.add(ea);
@@ -106,7 +106,7 @@ public Subscription schedule(final Action0 action, long delayTime, TimeUnit unit
                 return schedule(action);
             }
             if (isUnsubscribed()) {
-                return Subscriptions.empty();
+                return Subscriptions.unsubscribed();
             }
             ScheduledExecutorService service;
             if (executor instanceof ScheduledExecutorService) {

src/main/java/rx/schedulers/ImmediateScheduler.java

@@ -56,7 +56,7 @@ public Subscription schedule(Action0 action, long delayTime, TimeUnit unit) {
         @Override
         public Subscription schedule(Action0 action) {
             action.call();
-            return Subscriptions.empty();
+            return Subscriptions.unsubscribed();
         }
 
         @Override

src/main/java/rx/schedulers/TrampolineScheduler.java

@@ -68,7 +68,7 @@ public Subscription schedule(Action0 action, long delayTime, TimeUnit unit) {
 
         private Subscription enqueue(Action0 action, long execTime) {
             if (innerSubscription.isUnsubscribed()) {
-                return Subscriptions.empty();
+                return Subscriptions.unsubscribed();
             }
             final TimedAction timedAction = new TimedAction(action, execTime, COUNTER_UPDATER.incrementAndGet(TrampolineScheduler.this));
             queue.add(timedAction);
@@ -81,7 +81,7 @@ private Subscription enqueue(Action0 action, long execTime) {
                         polled.action.call();
                     }
                 } while (wip.decrementAndGet() > 0);
-                return Subscriptions.empty();
+                return Subscriptions.unsubscribed();
             } else {
                 // queue wasn't empty, a parent is already processing so we just add to the end of the queue
                 return Subscriptions.create(new Action0() {

src/main/java/rx/subscriptions/MultipleAssignmentSubscription.java

@@ -26,7 +26,7 @@
  */
 public final class MultipleAssignmentSubscription implements Subscription {
     /** The shared empty state. */
-    static final State EMPTY_STATE = new State(false, Subscriptions.empty());
+    static final State EMPTY_STATE = new State(false, Subscriptions.unsubscribed());
     volatile State state = EMPTY_STATE;
     static final AtomicReferenceFieldUpdater<MultipleAssignmentSubscription, State> STATE_UPDATER
             = AtomicReferenceFieldUpdater.newUpdater(MultipleAssignmentSubscription.class, State.class, "state");

src/main/java/rx/subscriptions/RefCountSubscription.java

@@ -80,7 +80,7 @@ public Subscription get() {
         do {
             oldState = state;
             if (oldState.isUnsubscribed) {
-                return Subscriptions.empty();
+                return Subscriptions.unsubscribed();
             } else {
                 newState = oldState.addChild();
             }

src/main/java/rx/subscriptions/SerialSubscription.java

@@ -24,7 +24,7 @@
  * the previous underlying subscription to be unsubscribed.
  */
 public final class SerialSubscription implements Subscription {
-    static final State EMPTY_STATE = new State(false, Subscriptions.empty());
+    static final State EMPTY_STATE = new State(false, Subscriptions.unsubscribed());
     volatile State state = EMPTY_STATE;
     static final AtomicReferenceFieldUpdater<SerialSubscription, State> STATE_UPDATER
             = AtomicReferenceFieldUpdater.newUpdater(SerialSubscription.class, State.class, "state");

src/main/java/rx/subscriptions/Subscriptions.java

@@ -19,6 +19,7 @@
 import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
 
 import rx.Subscription;
+import rx.annotations.Experimental;
 import rx.functions.Action0;
 import rx.functions.Actions;
 
@@ -30,12 +31,38 @@ private Subscriptions() {
         throw new IllegalStateException("No instances!");
     }
     /**
-     * Returns a {@link Subscription} that does nothing.
-     * 
-     * @return a {@link Subscription} that does nothing
+     * Returns a {@link Subscription} that <code>unsubscribe</code> does nothing except changing
+     * <code>isUnsubscribed</code> to true. It's stateful and <code>isUnsubscribed</code>
+     * indicates if <code>unsubscribe</code> is called, which is different from {@link #unsubscribed()}.
+     *
+     * <pre><code>
+     * Subscription empty = Subscriptions.empty();
+     * System.out.println(empty.isUnsubscribed()); // false
+     * empty.unsubscribe();
+     * System.out.println(empty.isUnsubscribed()); // true
+     * </code></pre>
+     *
+     * @return a {@link Subscription} that <code>unsubscribe</code> does nothing except changing
+     *         <code>isUnsubscribed</code> to true.
      */
     public static Subscription empty() {
-        return EMPTY;
+        return BooleanSubscription.create();
+    }
+
+    /**
+     * Returns a {@link Subscription} that <code>unsubscribe</code> does nothing but is already unsubscribed.
+     * Its <code>isUnsubscribed</code> always return true, which is different from {@link #empty()}.
+     *
+     * <pre><code>
+     * Subscription unsubscribed = Subscriptions.unsubscribed();
+     * System.out.println(unsubscribed.isUnsubscribed()); // true
+     * </code></pre>
+     *
+     * @return a {@link Subscription} that <code>unsubscribe</code> does nothing but is already unsubscribed.
+     */
+    @Experimental
+    public static Subscription unsubscribed() {
+        return UNSUBSCRIBED;
     }
 
     /**
@@ -124,16 +151,16 @@ public static CompositeSubscription from(Subscription... subscriptions) {
     /**
      * A {@link Subscription} that does nothing when its unsubscribe method is called.
      */
-    private static final Empty EMPTY = new Empty();
+    private static final Unsubscribed UNSUBSCRIBED = new Unsubscribed();
         /** Naming classes helps with debugging. */
-    private static final class Empty implements Subscription {
+    private static final class Unsubscribed implements Subscription {
         @Override
         public void unsubscribe() {
         }
 
         @Override
         public boolean isUnsubscribed() {
-            return false;
+            return true;
         }
     }
 }

src/test/java/rx/subscriptions/SubscriptionsTest.java

@@ -15,6 +15,8 @@
  */
 package rx.subscriptions;
 
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
@@ -35,4 +37,18 @@ public void testUnsubscribeOnlyOnce() {
         subscription.unsubscribe();
         verify(unsubscribe, times(1)).call();
     }
+
+    @Test
+    public void testEmpty() {
+        Subscription empty = Subscriptions.empty();
+        assertFalse(empty.isUnsubscribed());
+        empty.unsubscribe();
+        assertTrue(empty.isUnsubscribed());
+    }
+
+    @Test
+    public void testUnsubscribed() {
+        Subscription unsubscribed = Subscriptions.unsubscribed();
+        assertTrue(unsubscribed.isUnsubscribed());
+    }
 }