add concurrency protection to FuncWithErrors

Author: davidmoten

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

@@ -395,9 +395,11 @@ public static class FuncWithErrors implements Observable.OnSubscribe<String> {
         public void call(final Subscriber<? super String> o) {
             o.setProducer(new Producer() {
                 final AtomicLong req = new AtomicLong();
+                // 0 = not set, 1 = fast path, 2 = backpressure
+                final AtomicInteger path = new AtomicInteger(0);
                 @Override
                 public void request(long n) {
-                    if (n == Long.MAX_VALUE) {
+                    if (n == Long.MAX_VALUE && path.compareAndSet(0, 1)) {
                         o.onNext("beginningEveryTime");
                         int i = count.getAndIncrement();
                         if (i < numFailures) {
@@ -408,7 +410,7 @@ public void request(long n) {
                         }
                         return;
                     }
-                    if (n > 0 && req.getAndAdd(n) == 0) {
+                    if (n > 0 && req.getAndAdd(n) == 0 && (path.get() == 2 || path.compareAndSet(0, 2))) {
                         int i = count.getAndIncrement();
                         if (i < numFailures) {
                             o.onNext("beginningEveryTime");