Free upstream resources when default observer/subscriber is canceled. (#4385)

Author: JakeWharton

src/main/java/io/reactivex/observers/DefaultObserver.java

@@ -39,6 +39,7 @@ public final void onSubscribe(Disposable s) {
      */
     protected final void cancel() {
         s.dispose();
+        s = null;
     }
     /**
      * Called once the subscription has been set on this observer; override this

src/main/java/io/reactivex/subscribers/DefaultSubscriber.java

@@ -39,14 +39,18 @@ public final void onSubscribe(Subscription s) {
      * Requests from the upstream Subscription.
      */
     protected final void request(long n) {
-        s.request(n);
+        Subscription s = this.s;
+        if (s != null) {
+            s.request(n);
+        }
     }
 
     /**
      * Cancels the upstream's Subscription.
      */
     protected final void cancel() {
         s.cancel();
+        s = null;
     }
     /**
      * Called once the subscription has been set on this observer; override this