don't decrement if consumerCapacity is 0

Author: davidmoten

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

@@ -44,6 +44,7 @@
 import rx.Producer;
 import rx.Scheduler;
 import rx.Subscriber;
+import rx.exceptions.MissingBackpressureException;
 import rx.functions.Action0;
 import rx.functions.Func1;
 import rx.functions.Func2;
@@ -238,11 +239,16 @@ public void onNext(T v) {
                             child.onNext(v);
                             while (true) {
                                 long cc = consumerCapacity.get();
-                                if (cc != Long.MAX_VALUE) {
-                                    if (consumerCapacity.compareAndSet(cc, cc -1)) {
+                                if (cc == 0) {
+                                    child.onError(new MissingBackpressureException(
+                                            "an item has arrived to this operator that was not requested, "
+                                                    + "please use backpressure aware operators upstream (or append .onBackpressureBuffer() or similar)"));
+                                    break;
+                                } else if (cc != Long.MAX_VALUE) {
+                                    if (consumerCapacity.compareAndSet(cc, cc - 1)) {
                                         break;
                                     }
-                                } else  {
+                                } else {
                                     break;
                                 }
                             }
@@ -320,10 +326,14 @@ public void onError(Throwable e) {
 
                     @Override
                     public void onNext(Object t) {
+                        // a restart instruction has arrived
                         if (!isLocked.get() && !child.isUnsubscribed()) {
+                            // if there are outstanding requests 
                             if (consumerCapacity.get() > 0) {
+                                // schedule resubscription
                                 worker.schedule(subscribeToSource);
                             } else {
+                                // otherwise we indicate that on the next request we should resubscribe
                                 resumeBoundary.compareAndSet(false, true);
                             }
                         }