use CAS loop

Author: davidmoten

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

@@ -236,9 +236,15 @@ public void onError(Throwable e) {
                     public void onNext(T v) {
                         if (!done) {
                             child.onNext(v);
-                            long cap = consumerCapacity.get();
-                            if (cap != Long.MAX_VALUE) {
-                                consumerCapacity.compareAndSet(cap, cap -1);
+                            while (true) {
+                                long cc = consumerCapacity.get();
+                                if (cc != Long.MAX_VALUE) {
+                                    if (consumerCapacity.compareAndSet(cc, cc -1)) {
+                                        break;
+                                    }
+                                } else  {
+                                    break;
+                                }
                             }
                         }
                     }