2.x: Fix excess item retention in the other replay components

src/main/java/io/reactivex/internal/operators/flowable/FlowableReplay.java

@@ -806,6 +806,15 @@ public final void complete() {
             truncateFinal();
         }
 
+        final void trimHead() {
+            Node head = get();
+            if (head.value != null) {
+                Node n = new Node(null, 0L);
+                n.lazySet(head.get());
+                set(n);
+            }
+        }
+
         @Override
         public final void replay(InnerSubscription<T> output) {
             synchronized (output) {
@@ -909,7 +918,7 @@ void truncate() {
          * based on its properties (i.e., truncate but the very last node).
          */
         void truncateFinal() {
-
+            trimHead();
         }
         /* test */ final  void collect(Collection<? super T> output) {
             Node n = getHead();

src/main/java/io/reactivex/internal/operators/observable/ObservableReplay.java

@@ -619,6 +619,16 @@ final void removeFirst() {
             // can't null out the head's value because of late replayers would see null
             setFirst(next);
         }
+
+        final void trimHead() {
+            Node head = get();
+            if (head.value != null) {
+                Node n = new Node(null);
+                n.lazySet(head.get());
+                set(n);
+            }
+        }
+
         /* test */ final void removeSome(int n) {
             Node head = get();
             while (n > 0) {
@@ -733,7 +743,7 @@ Object leaveTransform(Object value) {
          * based on its properties (i.e., truncate but the very last node).
          */
         void truncateFinal() {
-
+            trimHead();
         }
         /* test */ final  void collect(Collection<? super T> output) {
             Node n = getHead();

src/main/java/io/reactivex/processors/ReplayProcessor.java

@@ -21,7 +21,7 @@
 import org.reactivestreams.*;
 
 import io.reactivex.Scheduler;
-import io.reactivex.annotations.CheckReturnValue;
+import io.reactivex.annotations.*;
 import io.reactivex.internal.functions.ObjectHelper;
 import io.reactivex.internal.subscriptions.SubscriptionHelper;
 import io.reactivex.internal.util.*;
@@ -362,6 +362,24 @@ public Throwable getThrowable() {
         return null;
     }
 
+    /**
+     * Makes sure the item cached by the head node in a bounded
+     * ReplayProcessor is released (as it is never part of a replay).
+     * <p>
+     * By default, live bounded buffers will remember one item before
+     * the currently receivable one to ensure subscribers can always
+     * receive a continuous sequence of items. A terminated ReplayProcessor
+     * automatically releases this inaccessible item.
+     * <p>
+     * The method must be called sequentially, similar to the standard
+     * {@code onXXX} methods.
+     * @since 2.1.11 - experimental
+     */
+    @Experimental
+    public void cleanupBuffer() {
+        buffer.trimHead();
+    }
+
     /**
      * Returns a single value the Subject currently has or null if no such value exists.
      * <p>The method is thread-safe.
@@ -499,6 +517,12 @@ interface ReplayBuffer<T> {
         boolean isDone();
 
         Throwable getError();
+
+        /**
+         * Make sure an old inaccessible head value is released
+         * in a bounded buffer.
+         */
+        void trimHead();
     }
 
     static final class ReplaySubscription<T> extends AtomicInteger implements Subscription {
@@ -568,6 +592,11 @@ public void complete() {
             done = true;
         }
 
+        @Override
+        public void trimHead() {
+            // not applicable for an unbounded buffer
+        }
+
         @Override
         public T getValue() {
             int s = size;
@@ -771,14 +800,25 @@ public void next(T value) {
         @Override
         public void error(Throwable ex) {
             error = ex;
+            trimHead();
             done = true;
         }
 
         @Override
         public void complete() {
+            trimHead();
             done = true;
         }
 
+        @Override
+        public void trimHead() {
+            if (head.value != null) {
+                Node<T> n = new Node<T>(null);
+                n.lazySet(head.get());
+                head = n;
+            }
+        }
+
         @Override
         public boolean isDone() {
             return done;
@@ -992,19 +1032,39 @@ void trimFinal() {
             for (;;) {
                 TimedNode<T> next = h.get();
                 if (next == null) {
-                    head = h;
+                    if (h.value != null) {
+                        head = new TimedNode<T>(null, 0L);
+                    } else {
+                        head = h;
+                    }
                     break;
                 }
 
                 if (next.time > limit) {
-                    head = h;
+                    if (h.value != null) {
+                        TimedNode<T> n = new TimedNode<T>(null, 0L);
+                        n.lazySet(h.get());
+                        head = n;
+                    } else {
+                        head = h;
+                    }
                     break;
                 }
 
                 h = next;
             }
         }
 
+
+        @Override
+        public void trimHead() {
+            if (head.value != null) {
+                TimedNode<T> n = new TimedNode<T>(null, 0L);
+                n.lazySet(head.get());
+                head = n;
+            }
+        }
+
         @Override
         public void next(T value) {
             TimedNode<T> n = new TimedNode<T>(value, scheduler.now(unit));

src/test/java/io/reactivex/internal/operators/flowable/FlowableReplayTest.java

@@ -21,13 +21,13 @@
 import java.util.concurrent.*;
 import java.util.concurrent.atomic.*;
 
-import io.reactivex.annotations.NonNull;
 import org.junit.*;
 import org.mockito.InOrder;
 import org.reactivestreams.*;
 
 import io.reactivex.*;
 import io.reactivex.Scheduler.Worker;
+import io.reactivex.annotations.NonNull;
 import io.reactivex.disposables.Disposable;
 import io.reactivex.exceptions.TestException;
 import io.reactivex.flowables.ConnectableFlowable;
@@ -1775,4 +1775,172 @@ public void badRequest() {
             .replay()
         );
     }
+
+    @Test
+    public void noHeadRetentionCompleteSize() {
+        PublishProcessor<Integer> source = PublishProcessor.create();
+
+        FlowableReplay<Integer> co = (FlowableReplay<Integer>)source
+                .replay(1);
+
+        // the backpressure coordination would not accept items from source otherwise
+        co.test();
+
+        co.connect();
+
+        BoundedReplayBuffer<Integer> buf = (BoundedReplayBuffer<Integer>)(co.current.get().buffer);
+
+        source.onNext(1);
+        source.onNext(2);
+        source.onComplete();
+
+        assertNull(buf.get().value);
+
+        Object o = buf.get();
+
+        buf.trimHead();
+
+        assertSame(o, buf.get());
+    }
+
+    @Test
+    public void noHeadRetentionErrorSize() {
+        PublishProcessor<Integer> source = PublishProcessor.create();
+
+        FlowableReplay<Integer> co = (FlowableReplay<Integer>)source
+                .replay(1);
+
+        co.test();
+
+        co.connect();
+
+        BoundedReplayBuffer<Integer> buf = (BoundedReplayBuffer<Integer>)(co.current.get().buffer);
+
+        source.onNext(1);
+        source.onNext(2);
+        source.onError(new TestException());
+
+        assertNull(buf.get().value);
+
+        Object o = buf.get();
+
+        buf.trimHead();
+
+        assertSame(o, buf.get());
+    }
+
+    @Test
+    public void noHeadRetentionSize() {
+        PublishProcessor<Integer> source = PublishProcessor.create();
+
+        FlowableReplay<Integer> co = (FlowableReplay<Integer>)source
+                .replay(1);
+
+        co.test();
+
+        co.connect();
+
+        BoundedReplayBuffer<Integer> buf = (BoundedReplayBuffer<Integer>)(co.current.get().buffer);
+
+        source.onNext(1);
+        source.onNext(2);
+
+        assertNotNull(buf.get().value);
+
+        buf.trimHead();
+
+        assertNull(buf.get().value);
+
+        Object o = buf.get();
+
+        buf.trimHead();
+
+        assertSame(o, buf.get());
+    }
+
+    @Test
+    public void noHeadRetentionCompleteTime() {
+        PublishProcessor<Integer> source = PublishProcessor.create();
+
+        FlowableReplay<Integer> co = (FlowableReplay<Integer>)source
+                .replay(1, TimeUnit.MINUTES, Schedulers.computation());
+
+        co.test();
+
+        co.connect();
+
+        BoundedReplayBuffer<Integer> buf = (BoundedReplayBuffer<Integer>)(co.current.get().buffer);
+
+        source.onNext(1);
+        source.onNext(2);
+        source.onComplete();
+
+        assertNull(buf.get().value);
+
+        Object o = buf.get();
+
+        buf.trimHead();
+
+        assertSame(o, buf.get());
+    }
+
+    @Test
+    public void noHeadRetentionErrorTime() {
+        PublishProcessor<Integer> source = PublishProcessor.create();
+
+        FlowableReplay<Integer> co = (FlowableReplay<Integer>)source
+                .replay(1, TimeUnit.MINUTES, Schedulers.computation());
+
+        co.test();
+
+        co.connect();
+
+        BoundedReplayBuffer<Integer> buf = (BoundedReplayBuffer<Integer>)(co.current.get().buffer);
+
+        source.onNext(1);
+        source.onNext(2);
+        source.onError(new TestException());
+
+        assertNull(buf.get().value);
+
+        Object o = buf.get();
+
+        buf.trimHead();
+
+        assertSame(o, buf.get());
+    }
+
+    @Test
+    public void noHeadRetentionTime() {
+        TestScheduler sch = new TestScheduler();
+
+        PublishProcessor<Integer> source = PublishProcessor.create();
+
+        FlowableReplay<Integer> co = (FlowableReplay<Integer>)source
+                .replay(1, TimeUnit.MILLISECONDS, sch);
+
+        co.test();
+
+        co.connect();
+
+        BoundedReplayBuffer<Integer> buf = (BoundedReplayBuffer<Integer>)(co.current.get().buffer);
+
+        source.onNext(1);
+
+        sch.advanceTimeBy(2, TimeUnit.MILLISECONDS);
+
+        source.onNext(2);
+
+        assertNotNull(buf.get().value);
+
+        buf.trimHead();
+
+        assertNull(buf.get().value);
+
+        Object o = buf.get();
+
+        buf.trimHead();
+
+        assertSame(o, buf.get());
+    }
 }