Revert "cache now supports backpressure"

This reverts commit 18ff5af.

Author: abersnaze

src/main/java/rx/Observable.java

@@ -3594,7 +3594,7 @@ public final <B> Observable<List<T>> buffer(Observable<B> boundary, int initialC
      * @see <a href="http://reactivex.io/documentation/operators/replay.html">ReactiveX operators documentation: Replay</a>
      */
     public final Observable<T> cache() {
-        return CachedObservable.from(this);
+        return create(new OnSubscribeCache<T>(this));
     }
 
     /**
@@ -3629,7 +3629,7 @@ public final Observable<T> cache() {
      * @see <a href="http://reactivex.io/documentation/operators/replay.html">ReactiveX operators documentation: Replay</a>
      */
     public final Observable<T> cache(int capacityHint) {
-        return CachedObservable.from(this, capacityHint);
+        return create(new OnSubscribeCache<T>(this, capacityHint));
     }
 
     /**

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

@@ -0,0 +1,76 @@
+/**
+ * Copyright 2014 Netflix, Inc.
+ * 
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package rx.internal.operators;
+
+import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
+
+import rx.Observable;
+import rx.Observable.OnSubscribe;
+import rx.Subscriber;
+import rx.subjects.ReplaySubject;
+import rx.subjects.Subject;
+
+/**
+ * This method has similar behavior to {@link Observable#replay()} except that this auto-subscribes
+ * to the source Observable rather than returning a connectable Observable.
+ * <p>
+ * <img width="640" src="https://github.com/ReactiveX/RxJava/wiki/images/rx-operators/cache.png" alt="">
+ * <p>
+ * This is useful with an Observable that you want to cache responses when you can't control the
+ * subscribe/unsubscribe behavior of all the Observers.
+ * <p>
+ * <em>Note:</em> You sacrifice the ability to unsubscribe from the origin when you use this operator, so be
+ * careful not to use this operator on Observables that emit infinite or very large numbers of
+ * items, as this will use up memory.
+ * 
+ * @param <T>
+ *            the cached value type
+ */
+public final class OnSubscribeCache<T> implements OnSubscribe<T> {
+    protected final Observable<? extends T> source;
+    protected final Subject<? super T, ? extends T> cache;
+    volatile int sourceSubscribed;
+    @SuppressWarnings("rawtypes")
+    static final AtomicIntegerFieldUpdater<OnSubscribeCache> SRC_SUBSCRIBED_UPDATER
+            = AtomicIntegerFieldUpdater.newUpdater(OnSubscribeCache.class, "sourceSubscribed");
+
+    public OnSubscribeCache(Observable<? extends T> source) {
+        this(source, ReplaySubject.<T> create());
+    }
+
+    public OnSubscribeCache(Observable<? extends T> source, int capacity) {
+        this(source, ReplaySubject.<T> create(capacity));
+    }
+
+    /* accessible to tests */OnSubscribeCache(Observable<? extends T> source, Subject<? super T, ? extends T> cache) {
+        this.source = source;
+        this.cache = cache;
+    }
+
+    @Override
+    public void call(Subscriber<? super T> s) {
+        if (SRC_SUBSCRIBED_UPDATER.compareAndSet(this, 0, 1)) {
+            source.subscribe(cache);
+            /*
+             * Note that we will never unsubscribe from 'source' unless we receive `onCompleted` or `onError`,
+             * as we want to receive and cache all of its values.
+             * 
+             * This means this should never be used on an infinite or very large sequence, similar to toList().
+             */
+        }
+        cache.unsafeSubscribe(s);
+    }
+}